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Why do people drink coffee? I realize this seems like a preposterous question, especially to a reader of a coffee-themed newspaper. “Because we love it.” is the automatic response. But why? Why do we love coffee so much? It’s a simple question without an obvious answer: coffee doesn’t provide much nutrition, it’s considered by most to be an acquired taste, and it takes considerable effort to grow, process, roast, and prepare. But, despite all that, it’s beloved by millions.

I began investigating this paradox in earnest when, 38 years ago I got my first job as a barista. I had already fallen in love with coffee, but I noticed that the customers in my shop were a diverse and varied bunch- they loved coffee too, but many had very different reasons than I did. I saw that each had their own motivations, likes, and dislikes about coffee. And I quickly realized that to be a good barista, I needed to understand: what makes these people- my customers- love coffee?

Before long, I became a coffee lifer, and this question motivated my professional career. Today, I research coffee as my job, which helps- we’ll get to that in a moment. But I’m also a lover of history, particularly the history of the things we eat and drink. The past reveals so much about us: why we eat the things we eat, what we value and reject, what we love and what we hate. So, let’s start at the beginning.

The Discovery of Coffee: The Energy-Giving Drink

Coffea arabica, the species of coffee human beings first discovered and consumed, grows in only one place: the lush mountain forests that cover what is now Southern Ethiopia and South Sudan. People didn’t keep written records of the discovery and earliest use of coffee, so we have only oral history to rely upon. The most commonly told tale is of a goatherd named Kaldi, who was letting his goats munch on the forest’s shrubs. At some point, he noticed his goats acting differently- they were frolicking and playing more than usual, even dancing. Investigating further, he saw they were feeding on little red berries from a waxy-leaved bush, and being courageous, Kaldi decided to try some himself. Soon he was frolicking and dancing right along with the goats. A passing monk saw the scene, and deduced that the berries had caused the energetic outburst of Kaldi and his flock. Gathering some of the fruits himself, the monk used the stimulating property of the berries to keep him awake during his long prayerful nights. Coffee had been discovered.

This origin tale, like most myths, doesn’t qualify as history. But what myths do is get to the heart of things- they reveal what we think is important, our deepest values and principles. And, clearly, the most important thing about coffee for the goats, for Kaldi, and for the monk was energy. The coffee fruit seemed to be a magical source of power- quite different from food or wine. Coffee made the goats frolic, made Kaldi dance, and made the monk wakeful. The Kaldi mythos tells us what was important to the ancient Ethiopians about coffee: and that important thing was energy.

We get our first written records of coffee a few hundred years later, when the seeds of the coffee plant had made their way to Yemen, just across the Red Sea from Ethiopia. The ancient Yemeni scholar Abd al-Qadir al-Jaziri wrote the very first recorded history of coffee, and noted it had been brought to Yemen by the Sufi mufti Jamal-al-Din al-Dhabhani. Al-Jaziri even gave us the reason: “(al-Dhabani) found that among its properties was that it drove away fatigue and lethargy, and brought to the body a certain sprightliness and vigour.” Clearly, these men saw in coffee the same thing Kaldi had- stimulation, wakefulness, and energy.

Adopting a Healthful Habit

Coffee soon developed another reputation as well. Our first European report of coffee comes from Leonhard Rauwolf, a German botanist and physician who visited Yemen in 1573. He described coffee as “A beverage as black as ink, useful against numerous illnesses, particularly those of the stomach. Its consumers take it in the morning, quite frankly, in a porcelain cup passed around and from which each one drinks a cupful.” Rauwolf didn’t mention energy, but he did mention health. Coffee in Yemen and larger Arabia developed a reputation as a healthful beverage, due at least in part to its bitterness- bitter foods (and beverages) were always thought to be good, especially for digestion. Coffee gave you energy, but it was also good for you.

The Spread of a Social Activity

As coffee became a permanent part of the Arabian lifestyle, its use spread throughout the culture. And, as Rauwolf mentioned, coffee began to be consumed by people together, not in solitude at home. Soon, a special venue emerged called the maqha, a public place for drinking coffee. These early coffee-houses became social hubs in a culture that was previously home-centered- the very nature of coffee was seen as a driver for social togetherness and conviviality. Illustrations of maqhas of the period- we now call them coffee-houses- show people sitting in circles drinking coffee, discussing news, and enjoying each others’ company. Even today in Ethiopia, coffee is consumed ceremonially as a structured social event, where discussion and conversation are expected and encouraged.

Coffee wasn’t just an energy-giving, healthful drink, it was also the driver for an entirely new social space: the coffee house.

The Perception of Deliciousness

As coffee drinking and coffee houses spread, we begin to see the fourth of coffee’s properties to be celebrated- its taste. In Arabia, coffee was prepared lightly roasted and brewed like tea, but as coffee spread to Turkey it began to be roasted darker and brewed stronger. This was a flavor preference, and illustrations of the time show coffee as a delectable, enjoyable indulgence. By the time coffee was introduced to Europe, its flavor was legendary- my own personal favorite ode to coffee flavor comes from the libretto of the 18th century operetta we now call the Coffee Cantata, where the main character, a young girl named Lieschen, effuses:

Mm! how sweet the coffee tastes,

more delicious than a thousand kisses,

Sweeter still than muscatel wine.

Coffee, coffee I must have,

and if someone wishes to give me a treat,

ah, then pour me out some coffee!

-from ”Schweigt stille, plaudert nicht”, the “Coffee Cantata”, music by J.S. Bach, lyrics by Picander, 1735

There we have them: energy, health, social interaction, and flavor; the four elements of coffee that our historical ancestors valued. These were the attributes that made coffee beloved to the Ethiopian and Yemeni discoverers of coffee, and created the coffee culture that rapidly spread throughout the world. These were the things about coffee beloved by the coffee-house patrons of the Ottoman empire and the earliest coffee-drinkers of Europe.

But what about today? I mentioned earlier that I now do coffee research. One of these areas of study is consumer research- that is to say, the search to understand what drives peoples’ preferences in coffee. Several years ago, we at the Specialty Coffee Association supported a ‘focus group’ activity, asking a group of consumers to tell us why they loved coffee. In addition to interviews, we gave the coffee lovers scissors, glue, and a big pile of magazines, asking them to make personal, custom collages about coffee. A few hours later, we got a bunch of images like this one:

I loved these images; they gave us a glimpse into people’s hearts as well as their minds. “Dark Energy” the collage above said- expressing no doubt about what “energy” the consumer was talking about. It was the very same energy discovered by Kaldi and celebrated by the mufti al-Dhabhani. Hundreds of years later, the feeling was the same. Dark, thrilling, vigorous, caffeinated energy.

The rest of the collages differed depending on the person. Some depicted friends drinking coffee together. Others showed us a coffee-driven lifestyle built around health and sustainability. Still others cut out words like “rich”, “yummy”, and “pleasure”; evoking the delicious sensory experience of coffee drinking. In the end, we noticed the collages sorted themselves into exactly four familiar categories: some about energy, others about health, some about social interaction, and many about flavor. Four categories- just like the coffee drinkers of the 16th century.

Energy, health, flavor, and social interaction. After more than three decades in coffee, these four concepts ring true- they are the things we love about coffee, the reasons why coffee is the first thing we think about in the morning, and the reason people like me have chosen coffee to build a life around. And, it seems that this has been true since the very beginning.

My grandfather, born Vincenzo Giuliano, grew up the child of Sicilian immigrants in Wakefield, Massachusetts. It was a solid and loving family, but soon, tragedy: when my grandfather was 8, his father died of heart failure, leaving him, his mother, and six siblings without a breadwinner. A few years later, the Great Depression hit. Before long, my grandfather left school to go to work. He was a teenager, first finding employment as a grocery clerk, but later landing a job as a fabric cutter at the Leopold Morse Clothing Manufacturing Company of Boston, Massachusetts. Leopold Morse was a Jewish company, a part of what is known in Yiddish as the “schmatta business"- the trade in cloth and clothes. Fabric cutting was a dangerous occupation: giant blades and power saws were used to trim the cloth into patterns for sewing, and the cutters had an industrial-revolution swagger and camaraderie. Though my grandfather was the odd man- a Sicilian Baptist in a Jewish sweatshop- he was embraced and included by the other men; a gesture he never forgot as he grew older. Over time, he learned the clothes-making trade: how to turn a design into a pattern, how to use the pattern to cut hundreds of pieces of cloth at a time, how to assemble those pieces, sewing them into perfect pants, dresses, and shirts. It was an industry of chalk lines, paper cutouts, cloth forms, steel blades, iron sewing machines, and stacks and stacks of cloth. He was lucky to have the work- it was the great depression after all- and he was luckier still to be learning a trade.

My grandfather- standing, far right in all white- with the other fabric cutters of the Leopold Morse Clothing Manufacturing Company of Boston, Mass. 1934.

Anyway, he must have developed his coffee habit during this period. Coffee was the lifeblood of the industrial revolution and its factories: it kept workers alert while operating the almost comically hazardous heavy equipment. The so-called “coffee break” was invented around this time- coffee drinking with one’s coworkers promoted teamwork and focus, and raised flagging spirits in the punishing environment of the sweatshop. My grandfather adopted the name Jimmy, and except for a temporary period of working in shipyards during World War II, he became a lifelong clothes-maker. During the postwar economic boom, he took a risk and opened his own small clothing factory in Los Angeles. By all accounts, he was a kind and focused boss. The (male) fabric cutters and the (female) sewers included family members and local workers alike, and he treated them with respect. I’m told he drank an shocking amount of coffee during this period: it was his beverage of choice at meals, his workday reviver, and his constant companion.

By the time I knew him, his name had changed again: it became nannu, Sicilian for grandfather. I was nannu’s second grandchild (my cousin Vince, his first, was named after him). Nannu suffered his own nearly fatal heart attack in 1973, after nearly 40 years of hard work, and he retired. His illness made his tall frame thin and weak, but he remained kind and charismatic. He and my nanna moved into a small apartment behind our house, and I began spending time with them after school.

Neither my nannu’s retirement nor his heart attack reduced his coffee consumption one bit. He was a legendary coffee drinker- everyone knew how much coffee he drank. He would make a pot in the morning, and drink the whole thing during breakfast, with biscotti or cereal. He then made a second pot, which was poured into a red-and-yellow tartan Thermos, just like the one at the Smithsonian. This coffee-filled Thermos with the coffee-cup lid was his companion for the rest of the day. He carried his coffee with him- the vacuum-insulated bottle kept his coffee hot (or cold during the summer months, when he drank iced coffee instead).

On weekends, I would run the few steps to nannu and nanna’s house, just behind ours. My glorious grandmother would feed me biscotti and milk (with a splash of coffee on occasion), while nannu would plan our day. We might work in the yard (my job was picking weeds), but more often we did errands- visiting hardware or grocery stores, picking up little things the family needed. Between errands, we would “pay visits”. My grandparents had a vast network of family and friends in the area- mostly Sicilians from Wakefield who relocated to California during the war- and a major priority was visiting friends and family to keep in touch. I loved these visits: greatest-generation houses were invariably neat and smelled good, and they would offer cookies or cake to a polite kid like me. The adults drank coffee and visited, while I sat still and listened.

As we drove between errands and visits, the red-and-yellow-tartan Thermos sat on the front seat of the car, right between nannu and me. And every once in a while, nannu would spot a park bench, his favorite place for a coffee break. He would pull the car over, and we would trundle to the bench, his leathery hand holding mine. We perched on the wooden slats, nannu drinking coffee and revealing the napkin-wrapped biscotti he kept hidden somewhere. These moments- sitting beside him drinking coffee on a park bench- are my most treasured childhood memory. The feeling warms me still- the coffee, the leathery hand, sitting quietly in the park next to an old man. I could smell the coffee on his breath as we talked, and I would watch as he poured coffee from the red-and-yellow tartan Thermos into the little cup.

I can’t remember exactly what we talked about. He must have told me stories- he was a good storyteller, and I know a lot of things only he could have imparted to me. I know about how he played trombone with the town band as a teenager, and I know that his cousin Fat the Barber had a haircut shop on Water street in Wakefield. I know he loved his wife- my nanna- and I know that he loved me.

From time to time, I wonder if this is why I chose coffee as my career. Nannu died when I was 20- I was already working as a barista but was pursuing a path as a musician at the time. Among the last words nannu said to me- while he was sick in the hospital- were “keep playing music, you’re good at it.” But it turned out music wasn’t for me, coffee was. I suppose he would have been happy about this turn of events, and I suppose he would have loved the coffee I would have brought them. I imagine he would have brewed it and carried it with him in his Thermos.

After nannu’s death, we lost track of his red-and-yellow-tartan Thermos. It might have gotten sold or given away- maybe it’s the one they have in the Smithsonian, I don’t know. My relationship with coffee is different than his- I don’t drink nearly as much of it, for one thing, and I pay attention to its particulars in a way that he did not. But I do love coffee, maybe just as much as he did. I love how coffee makes people connect- in coffee breaks at factories, at coffee shops on the way to work, during afternoon visits between friends at home or at the café. The bittersweet liquid stimulates us and makes us alert and chatty, and it tastes good, but it also bonds us in a way that other drinks don’t. Nannu knew this- coffee connected him with his wife over breakfast, his friends during visits, and with his grandson while sitting on a park bench. Our coffee breaks weren’t just for him, they were for us.

A few years ago, I got my own red-and-yellow-tartan Thermos, and though I don’t drink nearly the volume of coffee my nannu did, I pour my second brew into the Thermos to keep it warm (or cold) for the rest of the day just as he taught me. I’ve even pulled over to a park bench once or twice, for a coffee break.

My red-and-yellow-tartan Thermos reminds me of those moments with my nannu, when we sat together in the park. I treasure that reminder. But it also teaches me about how powerful coffee can be as a connector between people. Though most of us begin drinking coffee for the caffeine and and eventually fall in love with the flavor, the reason we keep drinking it is because it connects us in a very special way.

I like to think that the Smithsonian knew all this when they added a beat up working-class red-and-yellow-tartan Thermos to their collection. I like to think that there is a curator somewhere whose grandfather had a coffee Thermos too, and understands it not only as a cultural artifact, but as a reminder of the human connections it fostered.

Saltiness in Coffee

Anyone who’s familiar with coffee descriptor culture (those label notes!) knows that there are many, many tastes and aromas in coffee. But saltiness? Yep. Believe it or not, right there on the lower left hand side of the Coffee Tasters’ Flavor Wheel, in bright white type, is “salty”. What this means is that the trained descriptive analysis panel who developed the terms used in the the wheel detected saltiness in several of the 100+ samples they tasted for the project.

That doesn’t mean salty taste is common in coffee. In fact, when we published the wheel, I- who had tasted coffee professionally for 20 years by that point- was skeptical about the existence of saltiness in coffee.

But my colleagues disagreed, pointing out that it is detected most commonly in dry-processed coffees. That’s interesting, but still: how could it be? The coffee plant doesn’t have salt in it! Turns out I was wrong about that. Well, probably wrong. Truth is, the scientific literature is extremely sketchy about the amount of salt that exists in coffee beans. What scientific research I could find wasn’t focused on salty taste, but on dietary sodium, and it seems there is a detectable amount of sodium in coffee. And, given that sodium chloride is the most common form of sodium in plants, it’s probably in the form of salt. There is potassium in coffee too, and potassium chloride tastes salty as well. One paper I found shows wide variations in sodium and potassium content of coffee, which supports the notion that saltiness might be an occasional phenomenon in coffee. Most often, the sodium and potassium in coffee are below the threshold of human perception for saltiness- but sometimes it seems to be high enough to perceive. Though far from conclusive, what I’ve found suggests that it’s plausible that coffee sometimes has enough salt to taste.

But regardless of whether the mechanism is clear, most every coffee taster I’ve met has perceived saltiness in coffee at some point. And most associate it with “natural” coffees, the kind of coffees that are dried in their fruit before milling. My colleague Mario actually documented the salty taste in his PhD research, and associated it with some kinds of microbial activity in coffee processing. His hypothesis is that the microbial activity consumes certain flavor precursors, revealing the pre-existing underlying saltiness of the coffee. I’ve heard others say they could taste the saltiness of a coffee when they make espresso with certain dry-processed coffees; something about concentrating coffee’s flavor in the espresso machine magnifies the saltiness.

All this is to say, I’ve let go of my skepticism. I’ve tasted salty coffees myself, and I’ve talked to enough sensory scientists and coffee tasters to convince me that it’s not an illusion- coffee saltiness is real and it’s very plausibly from traces of sodium chloride and potassium chloride in the coffee beans themselves. The next question- is that a good or a bad thing?

Salt in Your Coffee Brew

Though coffee and salt sound like a terrible combination, it turns out that salt’s unique sensory function can have a positive effect on coffee flavor. Scandinavians have known this for generations- it’s common there to add a pinch of salt to one’s coffee. This makes sense when you consider the phenomenon I mentioned in my earlier article on saltiness- salt can mask bitterness and sourness, while enhancing sweetness in foods and beverages. This is a good thing in coffee (and most foods). Adding just the right amount of salt to coffee- just a tiny bit- will brighten and sweeten its taste. This also raises the tantalizing idea that some coffees might seem exceptionally sweet because of their natural salt content, at least partially. Anyway, the right amount of salt seems to be about a half a gram per 1000ml, which is like 1/6 of a teaspoon, but your results may vary according to the coffee. Try it and see!

As I mentioned before, salty taste is one of the most under-studied phenomena in coffee. (Even within the subject of sensory mechanisms of coffee, which is under-studied itself!). Any food scientists within the sound of my voice take note- we’re still wondering about the mysterious, occasional salty taste in our coffees.

The origins of “Quality”

Our Western notion of quality comes from the classical era, when Greek philosophers were trying to figure out the nature of the world around them. In his text Kategorai, the philosopher Aristotle developed an idea he called poios. The idea was that everything in the world has properties: a rock might be heavy, or it might be white, or it might be rough. Cicero later translated this concept into Latin as qualitas, “a property of a thing”. Qualitas in Latin became “quality” in English. We still use this sense of the term “quality”, especially when talking about people; (i.e. “He has many positive qualities.”)

Ancient philosophers didn’t stop there, however. Because they were preoccupied with finding a rational source for morality, many became interested in the quality of being “good”. What made a property of a thing- a “quality”- good or bad? Aristotle’s teacher Plato developed a theory of forms, which posited that there must be a perfect essence that a thing could be close to or distant from. In this way, a thing could have a “high” quality, that is, closer to its ideal form, or “low” quality, distant from its perfect form.

Over time, we adopted this concept of “quality”, meaning distance from perfection or “degree of excellence”. By the middle ages, most Europeans were using “quality” in this way. The important thing here is that this term “quality” refers to both a property of a thing and also reflects an idea of how closely a thing conforms to its conceptual ideal.

So, let’s think about a chair. How should we think about its quality? Well, the main property- or “quality”- of a chair is that it supports a sitting person. Therefore, a high-quality chair- well designed and durable- is excellent at supporting a sitting person. A low-quality chair- fragile and rickety- is worse at supporting a sitting person. Easy, right? We can think of this as a functional idea of quality.

But as I mentioned, European philosophers didn’t want to stop at function- they were preoccupied with ideas like morality and beauty. They began to assert that if there existed ideal forms for “chair” or “rock”, there must be ideal forms for “moral” and “beautiful” too. They began to believe that there was an objective ideal of beauty, one that existed in the supernatural realm, which all natural objects could be compared to. Through study (and good breeding), even a mortal would be able to understand this supernatural form beauty, and therefore assess an object’s aesthetic quality as well as its functional quality. Just as a chair might be compared against an ideal of “supports a sitting person” to assess its functional quality, it might be compared against an ideal of “beauty” to assess its aesthetic quality. And the people most qualified to assess both types of quality? That would be those who had the free time to study both function and aesthetics, i.e. the upper classes. Plato was explicit about this: to him, only those who understood the “form of the good” were fit to rule. The European elite embraced their role as arbiters of quality- the “fine tastes” of the ruling classes applied to their evaluation of art, music, architecture, literature, and, yes, food. The “fine arts” were those that produced artifacts with purely aesthetic value, with little functional use (music, painting, poetry), and the “popular arts” or “applied arts”- or sometimes “crafts”- were those that produced artifacts with both functional value and aesthetic value (pottery, architecture, decorative arts, and cuisine).

The History of Food Quality

Imagine being a person living in the Middle Ages, trying to feed your family. You head to the market to buy some wheat flour to make bread. There, you might be offered two kinds of flour: one milled from wheat grains that were wholesome and unblemished, and another made from grains that had been infested with insects and rats. The insect parts and rat droppings made the second batch of flour taste funny and made it less healthful, while the first batch was pure and nourishing. It was natural to think of the first kind of flour as being closer to the ideal of flour-ness, and the second one as being distant to flour-ness. Therefore, the wholesome flour was called “high quality” and the infested flour “low quality”. This is, in essence, the “functional” definition of quality in practice: if a food is pure, wholesome, and serves its function of nourishment, it is of high quality.

This was exactly the original meaning of “quality” in food. But what about aesthetic value? Ordinary people didn’t concern themselves with that- they were worried about making sure their family was well fed with wholesome, nourishing food. The upper classes, on the other hand, had leisure time to contemplate both the function and the aesthetics of food, and they began to establish norms of aesthetic culinary quality. Brown bread- made from flour that was milled with the bran intact- seemed aesthetically inferior to white bread; so white bread became the “higher quality” choice. (for most of European history, elites ate white bread while peasants ate brown bread.) Ordinary wine was good enough for the working classes, so long as it wasn’t spoiled or adulterated. But “fine” wine was an aesthetic and intellectual pursuit- certain vintages were more aromatic and memorable; and classical artistic concepts like “balance” and “harmony” could be applied to wine just as they were to paintings or sculpture. An aesthetic concept of cuisine developed, applying the ideals of artistic beauty to food and drink, quite apart from the functional concept of quality. And just as music, art, and architecture became incredibly beautiful during the Renaissance, so too did cuisine, eventually developing into the sophisticated court cuisines of France, Italy, and Spain. This was the beginning of a bifurcated idea about food quality: a functional dimension (the food is wholesome and sound), and an aesthetic dimension (the food is beautifully delicious). It’s important to note that the senses of taste and smell are useful in assessing both dimensions: we use our senses to determine if a food has been spoiled or adulterated, and food must be at least somewhat tasty in order to be functionally edible. It is also our senses that lead to an appreciation of beauty in food- the delicate aromas of fine wines, the unique aromas of truffles or exotic spices, or the studied aesthetic of French pastry (that last one is notable- it led to a memorable legend about Marie Antoinette declaring that the poor should “eat cake”, a food which the elite believed commoners neither deserved nor could appreciate).

So, “quality” in food meant very different things depending on social class. To the commoner who had to worry about food adulteration and contamination, “good quality” meant “wholesome and safe”; a functional definition. To the wealthy elite who could take wholesomeness for granted, “good quality” came to mean “tastefully beautiful”, an aesthetic definition. As populations and food systems grew, many foods took on two parallel identities, a “common” identity that was mostly functional, and a “special” identity that was celebrated for its aesthetic beauty. A great example of this is cheese. Cheese in Europe was seen as food suitable for the poor, since milk was relatively inexpensive and easy to turn into a basic, nourishing cheese. Simple, “country” cheeses were commonplace, and were considered “good quality” if they were unspoiled, untainted, and reasonably tasty. However, another category of cheeses emerged- such as the Brie de Meaux of France and the Parmigiano Reggiano of Italy: highly specialized, expensive cheeses celebrated for their specific, unique character. In these cases, the term “high quality” instead signified the aesthetic value of their unique flavor.

The Aesthetics of the West Encounter the World

The European elite were very happy to live in a world where the rules of aesthetics were very clear and seemed absolute. However, as global exploration and trade increased encounters with the larger world, the classical ideal of a universal, supernatural aesthetic came under pressure. The music of China, for example, was clearly sophisticated and guided by a sense of beauty, but the Chinese musical aesthetic was much different from the European one. During the period we now call the Enlightenment, philosophers worked to evolve their ideas of aesthetics to include the amazing works of art they saw in Africa, Asia, the Americas and elsewhere. At the same time, food tastes had to undergo a similar evolution. New ingredients both confused and delighted European palates, and challenged established ideas of food quality. It was during this period that the enduring motto of differing tastes emerged: de gustibus non est disputandum, “in matters of taste there can be no dispute”, or, “there’s no accounting for taste.”2 Europeans began to think of aesthetics as less absolute, and more a function of culture.

So, entering the modern era, we still have our two distinct concepts of food quality: functional quality and aesthetic quality. Both of these ideas would be challenged by modernity. As food systems industrialized and became more anonymous, food adulteration and contamination became an even bigger problem. For example, in 1858 in New York, over 8,000 infants were killed by “swill milk”: watered-down low-quality milk that had been made artificially white with plaster. Coffee wasn’t immune to adulteration- ground coffee was stretched with sawdust, chicory, or even sand. Public outcry for more wholesome foods led to a number of food-purity reforms, culminating in the Pure Food and Drug Act of 1906, which outlawed all food adulteration and established the FDA to monitor food quality. But this was purely functional quality- the law was not intended to regulate food aesthetics. Large food businesses eventually embraced the idea of food safety and purity, establishing brands dedicated to these concepts.

Food-quality-as-aesthetics therefore remained a tradition exclusive to the wealthy for the first half of 20^th century. The leisure classes could afford to spend time developing tastes for special wines, cheeses, and dishes at elite restaurants and society luncheons. This all changed in the post-World War II era, when increasing prosperity in Europe and the United States made it possible for the middle classes to dine at restaurants, buy vintage wines, and drink specialty coffee. At the same time, Americans and Europeans alike began to take the hard-won achievements of the food purity and safety movement for granted. Food “quality”- which always invited confusion in its dual nature-was more confusing than ever. (When the USDA says it regulates meat “quality”, does that mean it regulates meat wholesomeness or meat flavor? If good wine is delicious and bad wine tastes like vinegar, does that mean a wine critic’s score is objective or subjective, functional or aesthetic?) Because delicious, high-quality foods were more available than ever, this very ubiquity led to confusion about what quality meant.

The answer, of course, was the same as it always was: the term “quality” means two different things in food. And it does in coffee, too.

A Philosophy of Coffee Quality

We use the term “quality” to describe the degree of excellence of a thing. This excellence can come in two dimensions: functional excellence (the functional dimension of quality) and aesthetic excellence (the aesthetic dimension of quality. Some purely functional objects have only one of these dimensions: take for example an air conditioner, which is valued for its function but not its beauty. A high-quality air conditioner is therefore one which cools air effectively and lasts a long time. An even better air conditioner would also be quiet and efficient. Other things are not functional, but purely aesthetic: a piece of music exists only to be beautiful (or at least aesthetically moving). Its quality can only be assessed in aesthetic terms. Because all foods can be both functional and beautiful, and coffee is a food, coffee can be both; and therefore the term “high quality” has both a functional meaning and an aesthetic one.

The Functional Dimension of Coffee Quality Explained

Coffee is the seed of a plant, and when roasted, ground, and extracted it forms a beverage that is stimulating and nourishing (although coffee has no caloric value, it provides antioxidants and other phytochemicals to coffee drinkers). Like all foods, coffee is sometimes damaged during growth or harvest, infested by pests or microbes, or otherwise contaminated or adulterated. These problems reduce the functional goodness and wholesomeness of coffee. A mold-damaged coffee can be toxic, as can a coffee contaminated with petroleum. A coffee that includes sticks, leaves, or husks is less “coffee-like” than a coffee made with only coffee seeds. A coffee that has been insect-ridden and left to rot during processing is likely to be foul-tasting and undrinkable. For this reason, the coffee trade has adopted a set of coffee standards based on the functional sense of the term: if coffee is wholesome and undamaged, it can be said to be “high quality”. One traditional industry shorthand for this concept is “clean, sound, and new”- you’ll find this phrase written into contracts and stenciled on coffee bags. “Clean” means purely coffee, without adulterants, “sound” means undamaged, and “new” means reasonably fresh. When coffee is of “low quality”, it is the opposite- contaminated with non-coffee material, damaged by pests or microbes, or so old it no longer tastes like coffee. We often call coffees of this kind “defective”, and the individual undesirable beans as “defects”, describing a coffee which is undesirable to most everyone. To meet the functional definition of “high quality”, a coffee needs only to be drinkably tasty- if it is wholesome and tastes like coffee, it can be said to be of high quality (another coffee-lingo phrase is UGQ- “usual good quality”).

The other thing about functional quality is that it is relatively easy to define, standardize, and objectify. Coffee quality standard systems generally work to define this idea of quality- measuring coffee’s ability to function as a coffee beverage.

The Aesthetic Dimension of Coffee Quality

Because coffee is perceived with the senses, and the senses can be delighted, coffee can also be beautiful (my friend Tim recently used the term “sublime”). This is a glorious thing: coffee can smell of flowers or nuts, it can taste like chocolate or like fruit, it can transport the drinker to a cherished memory or a faraway place. If you’re reading this piece, I probably don’t need to prove it to you, but I will anyway: in a recent focus group performed by the Specialty Coffee Association, a coffee consumer described coffee this way: “You can taste all the different notes...Strong, dark and deep, a little bitter... Body and flavor...No need to mask it with milk and sugar...spicy, smoky ...earthy, real, basic... substance... thickness... a certain bit of magic.” This experience goes far beyond the basic function of coffee into the realm of art. This is the aesthetic meaning of “quality” in coffee.

In order to contemplate aesthetic quality in the first place, a coffee needs to meet the functional definition of “high quality”. It would be rare- perhaps impossible- for a contaminated or adulterated coffee to be aesthetically inspiring. But most coffee lovers know that coffee that is “just coffee”, regardless of its functional quality, falls short of the aesthetic heights a great coffee can reach. We have a different mindset when evaluating aesthetic quality in coffee- we describe specific aromas and flavors, we talk about the place the coffee came from or the producer who grew it, we compare coffees to other great ones we’ve had in the past. We relate to these things in the same way we’d respond to music or sculpture- with admiration and enjoyment.

But one thing to remember about aesthetics- we know that ideas about beauty vary. Though functional quality is fairly straightforward, a judgement of aesthetic quality is not: it will depend largely on a person’s culture, preferences, experiences, physiology, and psychology. Just as we understand that aesthetic ideals about music, art, architecture, design, and fashion will vary from era to era, from culture to culture, and from person to person, so can we expect that aesthetic ideals in cuisine and coffee will vary in the same way. De gustibus non est disputandum, “in matters of taste there is no disagreement”, remember? I’ll give you a food example: imagine three loaves of bread; a baguette from Paris, a loaf of San Francisco Sourdough, and a shokupan from Japan. All are equivalent in terms of functional quality: they are all made from wholesome wheat, they are all nourishing, and they are all tasty. But the flavor and texture of these loaves is radically different- the crust of the baguette is shatteringly crisp while the sourdough is chewy, and the shokupan crust is tender. The crumb of the baguette is wheaty, the crumb of the sourdough is tangy, and the shokupan is sweet. Which one is aesthetically better? Most would acknowledge this as a matter of personal or cultural taste.

But to say tastes vary is not to say that the experience of aesthetic beauty is not real- in fact aesthetic experience is the most real experience many of us have in life. The gorgeousness of a sunset or Bach’s Air on the G String are the best things about being human. So it is with aesthetic quality in coffee- it is a very real thing and a real experience that people have- it’s just not the same for all people.

Unfortunately, because we use the term “quality” to describe both functional quality and aesthetic quality, we sometimes assume it’s as easy to standardize aesthetic quality as it is to standardize functional quality. But this is the very same mistake that Plato and the medieval European aristocracy made- assuming that beauty was objective, universal, and was known only to the elite. We now know better- we realize that beauty exists in the hearts of individual people, who can have widely differing views of aesthetics. We see this in coffee- some love the intense fruity, winy notes of a long-fermented anaerobic processed coffee, while others are intoxicated by the crystalline, floral clarity of a washed coffee from Yirgacheffe. Or a solid, sweet Guatemalan. Or a spicy, cedar-toned Indian coffee. You get the picture.

Separating our ideas about functional quality in coffee and aesthetic quality in coffee helps clarify exactly what we’re talking about, what we expect to be universal, and what we expect to vary from person to person.

The Value of Experts

As a coffee expert myself, the question looms: what role does the coffee expert- the cupper, barista, or roaster, have in identifying coffee quality? Unsurprisingly given the above, it’s very different depending on if you’re talking about functional or aesthetic quality. But experts are important in understanding both.

Experts have always been relied upon to evaluate functional quality in coffee. Experts learn coffee grading systems, and are tasked with actually doing the grading. We learn to identify defects in coffee, discern contaminants, measure bean size, and communicate it in a clear, understandable way. In this way, we provide a service to the market- systematically evaluating and reporting functional quality.

Experts are also important in understanding aesthetic quality, it just works in a different way. When experts evaluate a coffee’s beauty, they are acting more like an art critic than an agricultural grader. A coffee expert who is sharing their evaluation of a coffee’s aesthetic quality understands coffee tradition, artisanship, and the desires of a market. Just as a film critic puts themselves in the place of the audience, a coffee expert puts themselves in the place of a coffee drinker, and makes judgements with that in mind. And, just like art critics, coffee experts may develop a certain school of thought or expertise- just as an expert in ancient Greek ceramics is informed about aesthetic quality in a 2500 year old amphora, an expert in African coffees is going to have an informed opinion about aesthetic quality in a Kenyan coffee. And these experts provide a really important function to consumers- they help consumers learn new things about coffees, and might help them discover experiences they might not have had otherwise. A consumer who watches a video by James Hoffman or meets a coffee producer from Honduras might be inspired to try something unfamiliar, expanding their aesthetic horizons.

But we shouldn’t get it twisted: the aesthetic experience of coffee- or any beautiful thing- exists only in the heart of the person experiencing it. We experts do not decide what is aesthetically good, we only seek to understand, make an opinion, and communicate what we believe. A sense of humility is essential if we seek to be good judges of aesthetic quality in coffee.

I tell this story to confess my bias towards iced coffee. I loved my grandfather immeasurably, and I loved the smell of iced coffee as he drank it and the clink of ice cubes in his glass. But, when I first started working as a barista and learned to appreciate the complex, compelling flavor of truly special coffees, I found iced coffee disappointing. At the coffee bar where I worked, we simply dumped leftover hot coffee over ice, and this left us with bitter, flat, unpleasant iced coffee. I stopped drinking iced coffee then.

That is, until I first visited Japan in 1993. I’ll never forget the moment: I went for an afternoon treat of strawberry shortcake (it was on trend that year), and the “set” was served with a lovely, straight-sided glass of clear, crisp iced coffee. This was not the iced coffee of my grandfather, nor of my coffee shop: it was delicate, nuanced, sweet, elegant, refreshing, and crisp. It was an entirely new thing for me. I needed to understand this iced coffee.

Several years later, I met Mr. Hidetaka Hayashi of the Hayashi Coffee Institute, a leader in the nascent Japanese specialty coffee industry. Hayashi-san taught me about the ways iced coffee was made in Japan, and how that delicate, elegant, crisp flavor was achieved. I adapted his techniques to brew this style of coffee in the states; in tribute to the experience I called it “Japanese Iced Coffee”. Ever since then, I have been known as something of an evangelist for iced coffee, a mantle which I have worn with pride. (I made an instructional video about how to make Japanese iced coffee in 2012, which got over a million views IN JAPAN! I was so proud.)

I have just confessed to being a cold coffee evangelist, a fact you should know before reading any further. It goes without saying I am optimistic about cold coffee- I have predicted that by 2035, more than 50% of the total coffee consumed in the United States will be consumed cold. In 2020, when I first started making this prediction, cold coffee consumption averaged about 20%, which was already on the increase from previous years. (This includes various types of cold coffee, which includes “cold brew” and frozen drinks- anything served ice cold). Though some treated it as a bold claim, it was really pretty conservative: cold coffee had already been increasing in popularity since around 2000. 2016 was something of a turning point, and the popularity of cold brew pushed iced coffee drinks further into the mainstream. Cold Coffee has continued grow- though more moderately- since then. But what explains this phenomenon, why do I think it’s a good thing, and what does it mean for the specialty coffee community? Let me explain.

Cold coffee can be special.

The aesthetic value of a piping hot coffee can be remarkable: a warming, aromatic cup of pure enjoyment. So I understand the joy of a beautiful cup of hot coffee. But I love cold coffee just as passionately, maybe even more so.

Now, pouring coffee over ice doesn’t automatically make it better. In fact, it can make it worse: the bitterness and harshness of poorly-made coffee can be made more intense by serving it cold. But does serving coffee cold automatically make it worse? Some coffee professionals think so. I don’t. Here’s why.

Much of coffee’s beauty comes from its flavor, and since flavor is a combination of aroma and taste, the aromatics of coffee are crucially important. The thing about aroma is that it is based on volatiles, those compounds that are able to jump into the air and travel to your nose. And all volatile substances are more volatile when they are hot: the energy of heat makes molecules leap into the air, including aromatic ones. That’s why a cup of hot coffee will smell more intense than a cold one. This leads some people to assume cold coffee is less flavorful than hot coffee.

However, the story changes when coffee passes through your lips. Your mouth quickly brings anything it ingests to body temperature- it makes hot foods cooler and cold foods warmer. And by the time you’re swallowing a food or beverage, it has become pretty close to body temperature. If the drink is cold to begin with, the warming that happens in the mouth and throat causes a burst of volatile aromatics, which proceed up into the retronasal cavity from the throat. This is why a gulp of iced coffee is so powerfully flavorful! A sip of hot coffee follows the same path, however it’s lost some of its volatiles while it was steaming in your cup. At the end of the day, it’s pretty much a wash: though hot coffee is more aromatic in the cup than cold coffee, cold coffee can be more flavorful when actually drunk. Furthermore, certain volatiles are preserved better in certain brewing methods, like cold brew: research has even shown that coffee prepared by cold brewing tastes more floral than the same coffees prepared by hot brewing.

So, from a material perspective, there is no reason cold coffee can’t be great. But what about the experience? Though sometimes iced coffee prepared thoughtlessly is simply a vehicle for a caffeine hit, when prepared thoughtfully it can be sublime. While preparing to write this article, I spoke to a fellow iced coffee enthusiast who lovingly described the way cold cream falls through the ice cubes when poured into a glass. Speaking of glass, iced coffee is an opportunity to use a perfectly clear, straight-sided tumbler- I use a favorite highball glass for the purpose.

A favorite memory of iced coffee for me is a one summer I spent in New York City, when the days were scorching and the nights long and muggy. I would hand-brew a fresh glass of iced coffee every morning before braving the humid subway to work- it was bracing and stimulating, an absolute joy and a highlight of my day.

So, both the experience and flavor of iced coffee can be transporting and very, very special. What about practical needs?

Cold coffee is better from a practical perspective.

It is really, really difficult to serve hot beverages. Make a drink too hot, and you risk causing scalding injuries to your friends or customers. Serve it at a more moderate temperature, and hot coffee immediately begins to cool- the optimal window of hot coffee temperature is narrow and fleeting. There is a whole industry of insulated thermoses, heated mugs, and carafe warmers dedicated to keeping coffee hot for this reason. Many people- in desperation to regain that elusive ideal drinking temperature- resort to reheating coffee in the microwave, a bad idea. Cold coffee served over ice, however, is much more stable: an iced drink stays constant at around 0 degrees celsius for a half hour or more (we can thank the thermally stabilizing magic of phase transition for that). So, from a practical perspective- both in hospitality and home settings- iced coffee has some clear advantages. Coffee shops have been steadily learning the lesson that it can be easier to delight customers with a beautiful cold beverage than a temperamental hot cup. Some retail concepts are embracing a cold-coffee forward approach that promotes iced beverages over hot ones- or even dropping hot coffee altogether. Though this might seem crazy, it might also be an example of forward thinking. Here’s why:

Some cultures- like America’s- just plain prefer cold beverages.

Coffee is actually an outlier in the beverage space: it’s really the only beverage left that is usually served hot. Once upon a time in the United States, hot liquor drinks ruled the bar: hot rum punch was a commonplace, and the Tom and Jerry- an eggnog-style drink- was the craze of the 1820s. Toddies- like punches- were generally served hot. Whiskey and gin were often drunk “neat”, that is, plain and at room temperature. The introduction of the commercial ice industry changed everything- suddenly bars could serve drinks over ice, and customers loved it. Soon, the “cocktail” became defined as a liquor drink served shaken with ice or served over it, and cocktail bars installed massive troughs to hold ice within reach of the bartender. Tea followed a similar trajectory- originally enjoyed exclusively as a hot drink, iced tea was introduced as a novelty in the late 19th century. It caught on quick, and today, about 80% of tea in the United States is drunk iced. We drink water, soda, seltzer, and energy drinks ice-cold. Chocolate milk sales dwarf hot chocolate sales. Coffee is the last straggler, the only beverage left in the United States which is normally drunk hot. How long will this last? Probably not forever.

Coffee in the landscape of cold beverages.

As coffee asserts itself more firmly in the cold-beverage realm, it’s pitted against more traditional cold drinks like soda, sparkling water, and iced tea. The biggest market share in the gold-drink space- besides water- belongs to sugary sodas. However, soda consumption in the U.S. peaked in about 2000, and has been declining steadily since then. The gap has been filled by a number of drinks- flavored sparkling water, kombucha, and energy drinks are products that have grown sharply over the past 20 years. Cold coffee’s growth has been sporadic- with a big boost from cold brew in the 2010s, and slower growth since the pandemic. Rising awareness of the dangers of high sugar consumption seem to be a major factor in this trend, even though energy drinks, iced tea, and iced coffees are often just as sugary as soda. The good news is that iced coffee has a lot of potential as a low-sugar beverage alternative- it’s seen by most consumers as healthy, energy-giving, and appealing. Coffee hasn’t ever quite leveraged itself as an unsweet beverage to accompany meals- and this is a major opportunity for coffee. (Have you ever had a BLT and a glass of iced coffee? Might be the best lunch ever.)

So, assuming the winds of change are blowing towards a future of delicious iced coffees served in homes, offices and coffee shops, how will this change the landscape of the specialty coffee world? Here are some predictions:

Cold Coffee will Change The Architecture of the Coffee Shop.

Traditional coffee shop design is based on hot drinks. Usually, two pieces of equipment- the espresso machine and the filter coffee brewer- are placed front and center in a specialty coffee shop. These are both essentially hot water tanks. The workflow is generally designed around pouring cups of hot coffee or making cafe lattes. As cold-coffee popularity has grown, shops have generally squeezed a cold coffee server in there somewhere as an afterthought. Ice is another matter- few shops have had the foresight to install a cocktail-style ice trough beneath the bar, so fetching ice can sometimes require a trip to another part of the back bar. Not optimal.

Cold-centric coffee shops follow different design cues: they’re often built around ice machines, beverage dispensers, and kegs instead of brewers, urns, and espresso machines, even if the hot-drink equipment is still present. But coffee shop designs are right now in flux- after two decades of fairly homogenous coffee shop layouts, we’re in a new era of experimentation and creativity.

Cold Brew and Consumer Habits.

We’ve already seen the dramatic rise of cold RTD (ready-to-drink) coffees in the United States, playing catch-up with the well-established RTD coffee segment in Asia. My feeling is that this space is still developing, as people decide how to integrate ready-to drink coffee in their daily lives. Iced tea has had an amazing run in RTD formats- including both single-serving and larger bottles which are kept in the home refrigerator. Though sweet coffee-and-milk RTDs have been around for a while, unsweetened and nondairy coffee RTDs haven’t quite found their footing yet, despite the early success of iconic products like Stumptown’s Cold Brew stubby.

As for freshly-made cold coffee, an increasing number of home brewing devices- from pod machines to high-end brewers- have introduced cold-coffee functions, allowing consumers to easily make iced coffee and cold brew at home. I think there is a big opportunity here- though consumers are often very familiar with the ease of making good hot coffee at home, they often haven’t yet learned the basics of cold-coffee making.

Confusion and Calories- the obstacles to Cold Coffee Growth

The Frappuccino has been an undeniable 30-year success in the specialty coffee world, more or less defining the cold coffee space for decades. Unfortunately, this has meant that many equate iced coffee drinks definitively with what is effectively a coffee milkshake. Industry metrics have struggled with this for a long time- it’s hard to clarify the distinction between sweet/dairy cold coffee drinks and unsweet/nondairy cold coffee drinks while doing consumer research. And, though frozen sweetened coffee drinks can be amazingly delicious, the often pack a calorie wallop- sometimes 400 calories or more per drink. This isn’t sustainable as a daily beverage for health reasons, as diseases like diabetes and obesity continue to grow. Cold coffee sometimes has a hard time breaking out of the Frappuccino mold in specialty coffee shops- but specialty cafes are innovating all the time and discovering creative, delicious ways to deliver cold coffee to eager customers.

The Future of Cold Coffee.

All in all, I’m incredibly optimistic about cold coffee’s future. It seems inevitable to me that the segment will continue to grow, and is likely to become the dominant mode of coffee consumption- at least in some markets- within the next decade. This is true for the U.S. and elsewhere- Asia has had a well developed cold coffee market for years, and certain countries like Greece have embraced cold coffee drinks already. As the Baby Boomer generation- who tend to favor hot coffee- become a smaller population segment, they are being replaced in the consumer market by generations who tend to have a more positive attitude towards cold coffee. A lot of this is driven by Asian coffee trends- others have, just like me, been inspired by the delicious iced coffee drinks of Vietnam, Indonesia, and Japan, and want to integrate those experiences into daily life.

What’s coming? I reckon cold coffee preparation equipment, drink styles, and cup styles will continue to evolve (dare I hope for an equivalent of the Stanley Cup craze, but built around coffee?) The stage is set for a major cold-coffee play, that is, a specialty coffee company whose identity is built entirely around cold drinks.

I for one, am here for it.

Ask a coffee person, and their answer will likely be, “Well, coffee is the seed of a fruit, you know.” And this is unequivocally true. Coffee “beans” are the seeds of a fruit called the coffee cherry, which grow and ripen on the bush-like coffee tree. Aha! the logic goes, since coffee grows as the seeds of fruits, it must be that fruit we’re tasting. Or at least something like that, right?

Here we encounter our first problem: while it’s true that coffee beans are the seeds of a fruit, that’s also true of almonds (which grow as the pit of a peachlike fruit) and walnuts (which grow inside a different fruit). Most nuts are fruits, in fact. And If we’re speaking botanically, wheat, rice, corn, beans, and sesame are all “seeds of a fruit” too. And these foods aren’t often described as “fruity”. So, while the botanical reality of coffee as the seed of a fruit is an important clue, it doesn’t tell the whole story.

To explain the phenomenon of coffee fruitiness, we have to take a step back and think about the phenomenon of coffee flavor in the first place. Unroasted coffee seeds don’t taste much like fruit- if anything, they taste like nuggets of wood. To create coffee’s flavor, we need roasting, which sets off a complex chain of chemical reactions in the bean. These reactions create a kaleidoscope of flavor chemicals- substances that have a taste or smell to us humans. One important category of coffee chemicals are the acids- especially citric and acetic acids. And this is our first connection to the fruits- all of the produce we call fruits have acids, and in fact we evolved a taste for acidity precisely because our species loves to eat fruit. But acids themselves aren’t enough- they tend to taste simply “sour”, without the aromatic complexity of fruits. Citric acid, despite its name, isn’t only found in citrus fruits: strawberries, cherries, and raspberries have citric acid, too.

That’s where volatiles come in: chemicals that we can smell, which trigger the multisensory experience of flavor. The most common illustration of this phenomenon is the jellybean test: ask a friend to give you a fruit-flavored jellybean while your eyes are closed. Just before eating the jellybean, hold your nose tightly shut. If you eat the jellybean with a closed nose, it will taste unidentifiably sweet and sour. Boring. But open your nose and the flavor magically appears: the aroma turns sweet-sour into strawberry flavor, or blueberry flavor, or tangerine. Same with coffee- when we drink the brew, we smell and taste it at the same time, and our brains put the stimuli together in a mental image we call flavor.

Ok, you might say, I get the mechanics. But that still doesn’t explain why a coffee can have a flavor reminiscent of fruit. Why should we experience these chemical combinations as “like fruit” instead of “like coffee”? And for that matter, why should a few chemicals in an artificially flavored jellybean make us think of strawberry or tangerine, even when no strawberries or tangerines were used in making of the jellybean?

The answer is a wonderfully human phenomenon with an unpronounceable name: pareidolia. (pa-ray-DO-lee-ah). Pareidolia is our habit of perceiving things where they don’t actually exist. I mean they exist, they’re just not the things we perceive them to be. I’m not explaining this well. Here’s an example. In 1976, the Viking I spacecraft was making a flyby of the planet Mars, taking pictures of its surface and beaming them back to Earth. Among the photographs was this one:

Everyone saw it: in the upper middle of the image was a face. Plain as day. Although NASA scientists immediately explained the impression of a face as a trick of light and shadow playing on a Martian hill, many observers didn’t believe it: this was obviously a sculpture of a face on the surface of Mars. This photograph led to years of excited speculation about intelligent Martian activity, alien life, and other cosmic connections. However, 25 years later when a more detailed image was taken of the same hill, it looked like this:

No face this time, just a hill. Bummer. But why did we see the face the first time? The answer is pareidolia. Our brains look at faces all day long- we stare at faces on Zoom meetings, we clean our kids’ dirty faces, we have pictures of faces decorating our house. We are evolved and conditioned to recognize faces- faces of friends and family, of famous people, of dangerous enemies. And when we see the right combination of blurry light and shadow, BAM! we see a face. Pareidolia is why we see figures in clouds or hear spoken words in records played backwards. Our brain is constantly trying to make sense of the stimuli it receives, and when it finds a pattern it recognizes, it tells us so. We evolved pareidolia for a good reason- there is an evolutionary advantage to recognizing faces, plants, and animals. And if we’re going to make a mistake, a false positive is better than a false negative: to be frightened because a rock seen in dim light looks like a tiger is better than to not recognize a lion because it doesn’t look exactly like a tiger. This phenomenon is so common in the human experience that we have a whole language for it: we use the form of the simile to explain the experience of pareidolia. We say “that cloud looks like an elephant” or “that flute sounds like a bird”, even when we know there is no elephant in the sky or bird in the orchestra. We know our brains seek to find meaning in experience, even when that meaning is not literal.

Flavor works like this too. We learn to recognize tastes and smells through the foods we eat every day. Over time, we learn to recognize a certain patterns of smellable, tastable chemicals as “butter” or “toast” or “strawberry”. And we become so adept at this, and our mental file of flavor stimuli is so extensive, that we begin to perceive foods even where they don’t actually exist. And so it is with coffee- there are so many aromatic elements in the complex chemistry of coffee, that we begin to find reminders of fruits: when a combination of compounds we recognize from blueberries occurs in coffee, we say “it tastes like blueberry”, and so on. It’s pretty magical, and it’s really really cool. And it’s not that common in other foods- the uniquely complex aromatic character of coffee makes all this possible.

OK: now that we understand the phenomenon of fruit flavor in coffee, let’s focus on the stimuli themselves and where they come from. Coffee fruitiness originates from two main places: the metabolic chemistry of the coffee itself, and the processes coffee goes through after it is picked. (There is a third category of fruitiness in coffee which comes from intentional additives, but that’s a topic for another post.) On to the causes of fruit in coffee!

Coffee Growing, Metabolites and Fruitiness

Coffee is a plant, and all plants create metabolites as a part of their metabolism, our term for the life sustaining processes of any organism. When we pick the fruit, these chemicals remain in the seed throughout its processing and drying. The heat of later roasting sets up lots of reactions, where these metabolites interact with others, producing even more chemicals. These compounds interact and combine to create other compounds, and so on, creating a wild cascade of chemical reactions in the roast. Of the resulting chemistry, some acids remain, but more important are the volatile aromatics. There are dozens of these which contribute to fruity flavor: for example, benzaldehyde is a chemical that is present in coffee and both almonds and cherries, and can taste like either (think the smell of maraschino cherries). 3-methylbutanal is another, which can smell like banana or apricot at low concentrations, or cheese at higher concentrations. Coffee has terpenes like limonene which have a strongly fruity aroma- in fact limonene is the compound that gives the characteristic fruity flavor to Froot Loops cereal.

It’s tempting to look for a 1-1 relationship between these chemicals and flavors (limonene makes coffee taste like Froot Loops!) but the truth is much more complex: it’s the combination and context of compounds that makes the difference. In the context of a nut butter, benzaldehyde contributes to almond aroma, but in the context of fruit preserves it contributes to cherry flavor. In coffee, it can go either way, depending on what other compounds are present. With this in mind, it’s a miracle that we ever taste a flavor consistently at all- but get the right set of compounds and you’ll get an unmistakably identifiable flavor of luscious fruit.

Coffee Processing and Fruitiness

If there are metabolites that come from coffee growing, there are other compounds that result from coffee using its stored energy. This destructive metabolism is called catabolism, and this can create coffee flavors too. I mention this because during the well known “natural” processing technique, where coffee is allowed to ferment and dry in its fruit, fruity flavor can go off the charts. My respected friend Dr. Mario Roberto Fernandez Alduenda studied exactly this phenomenon, and showed that fruity-tasting esters resulted from catabolism- that is, decomposition- of coffee during the process. It’s very much like how a peach’s flavor can change as it sits on your counter- developing deeper, more complex, ripe-fruit flavors as it softens.

Speaking of winy, there is another factor here: microorganisms. Microbes like yeasts and bacteria are naturally attracted to the sweet flesh of fruits, and famously transform sugary fruit juices into alcohols and acids, which in turn form esters and a range of other flavorful compounds. During coffee’s fermentation stage, these microorganisms enter the fermentation tank or the fruit itself, creating precursors to fruity flavors. Remember, however, these are mostly precursors. Though some compounds might survive roasting and wind up in the cup, most don’t: the process of roasting converts coffee’s compounds to others, sometimes many times before the roast is finished.

So, fruity flavors can come from two main places: the coffee metabolism itself creates flavor precursors that are revealed in the roast, or coffee processing, catabolism, and microbiology create different flavor precursors. Expert coffee tasters learn to distinguish between these two kinds of fruitiness: the coffee itself tends to create flavors like citrus, blackcurrant, and passionfruit, while processing-related fruitiness tends to resemble blueberry, strawberry, mango, or wine. Coffees of both kinds are cherished for this fruitiness, which is why so many coffee labels mention fruits: they are an exciting feature of very special coffees.

That said, fruity coffees aren’t for everyone. Many love chocolate, nut, brown sugar, or vanilla notes in their coffee. But for those who love them, the fruited coffees are indeed special and one of the many miracles of coffee flavor.

Although Kenya adjoins Ethiopia, the indigenous origin of Coffea arabica, Kenyan coffee agriculture is relatively new. Coffee was first planted there in 1893, and it took quite a while to get popular- and that was the doing of the colonial British Empire. In its early years, coffee in Kenya was almost completely a colonial project- if you want a glimpse, check out the movie (or book) “Out of Africa”, a romantic tale of a colonial coffee farming enterprise.

As expanding coffee farms pushed their way up the foothills of Mount Kenya north of Nairobi, farms got less productive and riskier to manage. This is because high altitudes put extra stress on coffee trees, reducing their production. However, this same phenomenon does something else- it makes the coffee more delicious. This is the reason that coffee experts obsess about the altitude of coffee farms: all things being equal, altitude is a key predictor of coffee flavor.

Nowhere is this truer than in Kenya, where coffee from the mountains has an amazing intensity of flavor. And sometimes, in coffee from these highlands, a particular flavor emerges that exists nowhere else in the world. And nobody knows quite why.

Let me try to explain this flavor to you. You smell it first, when the coffee is grinding, and it hits you like a brick. It accompanies the familiar sweet-brown smell of coffee but is totally different. It’s definitely fruity, in a tangy, pointed way. You feel the tang in your nose and it makes your mouth instantly water. While brewing the coffee, the fruity aroma persists and seems to get riper and rounder. By the time the cup of coffee is ready, the flavor has totally permeated the coffee, your kitchen, and your mind. And each sip has it. It’s glorious.

Now let’s be clear about this: coffee descriptions can be imaginative, and often evoke fruit terms. That’s because coffee often has hints of fruity flavors. I say “hints” because that’s what they usually are- gentle wisps of citrus, or peach, or cherry. But the Kenyan highland coffee taste is a completely different animal- in the best coffees it demands notice: it is THERE and it wants you to TASTE IT.

And what do we call this flavor? An early Kenyan agricultural science paper shared by my friend Mario called it the “Solai taste”, after the highlands coffee-growing town of the same name. The paper explains that it is an “up country” flavor, known only to coffees from the mountains of central Kenya. I was introduced to this same flavor by British coffee exporters who called it “the blackcurrant taste”, their way of describing the flavor’s intense purplish fruitiness. (That’s a quintessentially British way of describing flavor- since the introduction of Ribena blackcurrant syrup during World War II, the British have something of an obsession with blackcurrant: in the UK you can buy blackcurrant gum, blackcurrant gelato, and the purple Skittles in Britain are blackcurrant instead of grape.) Americans generally lack any familiarity with blackcurrants, so to us, the flavor resembles something more like blackberry or boysenberry. Cranberry, maybe. But really, any of these fruit metaphors are inadequate: this flavor is its own thing, and it can only be found in coffees from the Kenyan highlands. It’s kind of magic.

“But there is no such thing as magic, Peter”, you might say. “Everything real is discoverable by science.” This may be true, but science hasn’t figured this one out yet. People have theories, however: and here are a few of them.

It’s the variety. Like any agricultural product, coffee farmers develop specific genetic strains of plants through selection and breeding. In wine we call these varietals, in everything else we call them varieties, and it’s what makes a Purple Cherokee tomato different from a Sungold tomato. Different varieties can drive an immense difference in flavor and appearance. Kenya has, over the years, developed several coffee varieties that are unique to the country, and two are often associated with the Kenya Highland Taste. These two varieties have odd names: SL-28 and SL-34.

These two varieties were named after “Scott Labs”, an old Kenyan agricultural research station, and they are considered the traditional varieties of Kenya. Trouble is, they can be susceptible to disease, and a given farm is often mixed with other more disease resistant varieties like Ruiru 11, Batian, and K7. Though most experts associate the Kenyan Highland Taste with the SL varieties, it’s not so simple: it’s hard to find single-variety coffee farms in the highlands, and sometimes all-SL coffees fail to have the flavor. So…

It’s the altitude. Kenya has some of the highest-altitude coffee farms in the world, and true to its name, the Kenyan Highlands Taste almost always comes from coffees grown in the highest Kenyan mountains. It certainly seems that the high altitude somehow unlocks the flavor from the coffee trees planted there. But there are high-altitude farms all over the world, and they never seem to have that signature taste. So maybe….

It’s the soil. Drive around the mountains of central Kenya and you’ll notice that the dirt is often a brilliant shade of orangey-red. These are called laterite soils, a unique kind of soil rich in iron and aluminum oxides which give it that lovely color.

Laterite soils are found most often in the tropics, and they seem well suited for coffee. Could it be that Kenyan highlands have a specific kind of laterite that creates the Highland Taste? Possibly. This brings us to our next hypothesis….

It’s phosphoric acid. Kenyan coffees are noted for having a pleasing flavor tasters call “acidity”. And some studies have shown that Kenyan coffees are more likely to have phosphoric acid than coffees from other origins. Could phosphorous in Kenyan soil lead to phosphoric acid in Kenyan coffees? And could this phosphoric acid be the cause of a uniquely fruity, tangy taste in coffee? It’s a tempting explanation, but unlikely. Phosphoric acid doesn’t taste like fruits, for one thing- it’s just sour. Second, systematically measured concentrations of phosphoric acid in Kenyan coffees aren’t all that different from other origins. Third, acid concentrations and “perceived” acidity don’t necessarily have a direct relationship- it’s much more complex than that. So, perhaps it’s not about agriculture at all. Maybe…

It’s the processing. All coffee is processed before export, and in Kenya most coffees are washed, that is, cleaned of their fruit layers before drying and milling. In many places, washing includes a fermentation phase, which can create fruity flavors in coffees. In Kenya, many highlands producers take an extra step, soaking the coffees after washing in clean water, a technique that is unknown elsewhere. Could it be that this step contributes to the Highland Taste? It seems possible. But more likely…

It is all of the above. The right genetics are critical but even the best genes rely on an interaction with the environment: for example, a hydrangea’s flower color depends on the chemistry of the soil it grows in. It seems most likely that a unique intersection of variety, altitude, soil, and processing combine to create the unique Kenyan Highland Taste. This is a testable thing- agricultural and sensory science are able to figure this kind of thing out- but nobody in the scientific literature has done it yet. From a scientific perspective, the Kenyan Highlands Taste is still an unsolved mystery.

Mysteries are fun, but this one is a risk. So long as we don’t know what causes this precious flavor, we run the risk of losing it. Like everywhere coffee grows, Kenya is susceptible to changes in prices, climate, and economic stability. Though coffees with the Kenyan Highland Taste sell for high prices, it’s rare for given farm or cooperative to produce them consistently- which makes them rare gems indeed. Even worse, these rare gems seem to be getting rarer: I hardly ever encounter the Kenyan Highlands Taste any more. People I trust who have decades of experience in Kenya have observed the same thing- the flavor seems to be slowly getting harder and harder to find.

That’s why I am so grateful for that cup from Thunguri via Solberg and Hansen- it gave me a tremendous amount of joy, and reminded me that the Kenyan Highland Taste is still one of the loveliest things in the world.

*thanks to Mario Fernandez-Alduenda and Mette-Marie Hansen for their valuable and interesting thoughts on this subject- it’s a wonderful thing to learn from respected friends.

Bitter is one of the five tastes perceived in the mouth. These are often called “basic tastes” since they have been seen as fundamental since the beginning of sensory science. One thing about basic tastes is: your taste buds detect dissolved substances in the mouth. So, you can think of your tongue as sort of a sophisticated chemical detection system, which organizes the chemicals it detects into one of five categories: sweet, sour, salty, umami, and bitter. We’ve covered sweet and sour in coffee already, but arguably bitter is more important than either of them. So important that we in specialty coffee…. ignore it. Wha? Let’s get into it.

The source of coffee’s bitterness

As I wrote earlier in the week, our bodies assign the sensation “bitter” to a wide variety of substances, mostly toxic phytochemicals, i.e. compounds found in plants. Though sweetness is about sugars, salty is about salts, umami is about proteins and sour is about acids, bitter is about A LOT of things. Your body assigns “bitter” to a wide variety of chemicals it doesn’t quite trust, which is why it’s such a common taste. (Have you ever wondered why basically all pills taste bitter, regardless of the medicine? That’s your body saying: “I detect a chemical and I’m pretty sure it’s not food.”) All chemicals are toxic in large doses and harmless in small doses, which is true for bitter compounds too. But many bitter-tasting compounds have bonus physiological properties. Take the alkaloid caffeine for example. It’s quite bitter, and plants developed it to be toxic to leaf-chewing insects. But small doses in humans give us a lovely stimulant effect. Thus, the paradox of bitterness- it can mean poison or it can mean benefit! This paradox is reflected in our taste preferences- we hate bitterness sometimes, but we easily develop a fondness for it, especially when we associate it with positive effects. And in no food is this paradox clearer than in coffee.

Coffee is bitter. No question about it. Food chemists have discovered that there are at least 30 bitter-tasting chemicals in roasted coffee, and these compounds are pretty diverse. That’s bitterness for you- hard to pin down. But there are a few categories that stand out, and are worth mentioning: they are caffeine, chlorogenic acids, and browning compounds.

As mentioned earlier, caffeine is bitter, and is also kind of the point of coffee to many people. Though decaffeinated coffee is great (and slightly less bitter), modulating caffeine in coffee is a little like modulating alcohol in wine- there are tradeoffs in both flavor and functional effect. But there isn’t that much caffeine in coffee, so it’s only responsible for a small part of coffee’s bitterness. Though decaf can be slightly less bitter, it’s not unbitter, so there must be other chemicals at work besides caffeine.

Chlorogenic acids are a special group of acids that are especially associated with coffee- they include quinic acid and caffeic acid, which might be familiar names if you’ve ever talked coffee chemistry. Though these acids are only slightly bitter in themselves, they break down during roasting into much bitterer-tasting compounds. Many of these tastes begin to appear early in the roast, which is why you sometimes get that unique sour-bitter taste in very light roasted coffee. But, because these compounds are created during roasting, they tend to accumulate over the course of the roast, becoming more intense in darker roasts. And, many of these particular bitter compounds are also the antioxidants that make coffee healthy- there’s that paradox again!

Speaking of roasting, heat makes coffee darker in two ways: a class of chemical reactions called Maillard reactions and a simpler process called sugar browning. Both reactions produce browning compounds, a general term that describes any brown-colored substance resulting from thermal transformation in coffee. Many of these compounds are bitter, so this is another reason coffee gets bitterer as it gets darker. That’s why we associate bitterness with dark roasted coffee.

All of these compounds exist in coffee naturally, and different coffees will have different chemistry. So, bitterness will vary from coffee to coffee. One thing is clear, however: the coffee species known as canephora or robusta has more caffeine and more chlorogenic acids than the arabica species does, so, all things equal, it will usually be more bitter.

Controlling Bitterness in Coffee

So, all coffee is bitter to some degree, and some coffees are bitterer than others. But bitterness can be controlled in a number of ways. For one thing, since bitterness is enhanced by dark roasting, you can always increase a coffee’s bitterness by roasting it darker. Conversely, light roasting will temper bitterness a bit. This trick works in another way as well: sweetness and sourness (aka acidity) tend to interfere with the perception of bitterness, and both of these are increased in light and medium roasts. So, moderate-to-light roasting will almost always equal reduced bitterness.

Second, research has shown that bitterness is modulated by changes in brewing styles. High extractions are correlated with high bitterness, which is the reason baristas talk about bitter “overextracted” coffees. Somewhat counter-intuitively, increasing the amount of coffee in your brew while reducing temperature and time will also reduce bitterness, maximizing acidity and fruity notes.

Third, one can always modify the cup of coffee itself. Sweetness reduces the ability to perceive bitterness, so a spoonful of sugar in a cup of coffee will cut the bitterness dramatically (that same spoonful of sugar helps the medicine go down, but that’s another story). Milk has a number of properties that dull bitter perception, which is one reason why it is so good at taming coffee’s bitterness- and many cultures can’t imagine drinking coffee without milk to temper it. Chocolatiers do the same thing- adding sugar and milk to chocolate to mute its bitterness.

But is bitterness in coffee good or bad?

Now we’re getting to the heart of the matter. You probably know what I’m going to say: bitterness in coffee can be both good and bad, depending. This is because of that good old bitterness paradox. People hate bitterness except when they love it. Bitterness equals unpleasant toxicity except when it means healthy and delicious. Enthusiasts add hops to beer to make it bitter, scarf down bitter 70% chocolate, and mix bitter matcha into their smoothies, but the uninitiated hate bitter IPAs, dark chocolate, or bitter tea.

Coffee’s no different. Certain coffee-drinking cultures love bitterness in coffee. Southern Italians are a great example of this: they traditionally mix bitter robusta coffees into their blends and roast dark, creating powerfully bitter espressi. But other traditions- even in Italy- avoid bitterness, choosing lighter roasts and arabica based blends. Experts and consumers alike have different sensitivities and preferences about bitterness, but most people like some kind of moderation in bitterness: bitter enough to taste like coffee, but not so bitter it’s unpleasant.

Unfortunately, the commercial coffee culture in the late 50s and early 60s in the US and elsewhere started to push the limits of people’s bitter tolerance. Coffee cheapness seemed important at the time, which led industrial coffee roasters to incorporate more bitter coffees- like cheaper robustas- into their blends. Coffee shops, seeking to scrimp on costs, extracted the heck out of these coffees, boosting bitterness even more. Coffee had gotten too bitter for its own good, and consumers began to avoid the drink. Coffee consumption began to decline.

The Specialty Coffee Revolution and the Bitterness Taboo

The stage was set for what we now call the Specialty Coffee revolution. Craft roasters began roasting less-bitter coffees and brewing them more conscientiously, creating more balanced cups. Since commodity coffee roasters at the time had so thoroughly embraced robusta for cost reasons, the specialty coffee movement focused on the arabica species as a defining feature. And, as specialty coffee gained popularity, it built around the ideal of talking about what was right with a coffee, rather than what was wrong with it. Here’s an example: in 1922, coffee writer Willam Ukers listed 11 flavor words coffee roasters used to describe coffees: acidy, bitter, smooth, neutral, flat, wild, grassy, groundy, sour, fermented, and hidey. Most of these have a negative valence. 65 years later, in his seminal “Coffee Cuppers’ Handbook”, specialty coffee pioneer Ted Lingle introduced a greatly expanded language for high-quality coffees, in which he focused on positive language and de-emphasized bitterness as a useful word for coffee. Describing his reasons for writing the book in 1986, he said, “I wanted to develop the ability to talk about flavor differences beyond, ‘it’s not bitter’.” In the book itself, he wrote,

“The primary basic taste sensations in the gustation of coffee are sweet, sour, and salt. The function of the bitter sensation serves only to modify or enhance the impression of the other three, except for low grade or darkly roasted coffees in which bitter becomes the dominant taste.”

In other words, bitterness was to be ignored in specialty coffee. Though Lingle and others acknowledged that bitterness was present in all coffee including specialty coffee, the mention of it became something of a taboo. The word “bitterness” did not appear on Lingle’s SCAA cupping form, although “sweetness” and “acidity” did. The “B” word wouldn’t appear on specialty coffee labels, and the celebrated “Third Wave” roasters in the 2000s sourced coffees with as little bitterness as possible, roasting extra-light to further avoid bitter tastes. Acidity and sweetness were in, bitterness was not. In the modern parlance, bitterness had been canceled.

Is coffee bitterness mounting a comeback?

The bitterness taboo in specialty coffee has its drawbacks. For one, all coffee is bitter to some degree, and to ignore the flavor completely is to lose the opportunity to measure it. For another, bitterness is often desirable in coffee, especially those blends intended to be used with milk. The recognition of these two things has allowed the term to slowly make its way into the specialty coffee lexicon. In 2010, Lingle himself helped create a tasting form intended to be used for robusta coffees which included bitterness, and in 2023 the SCA’s Coffee Value Assessment finally included “bitter” in its “main tastes” section.

And that may just be the beginning. As coffee styles get more diverse and innovative, many coffee companies are taking a more bitter-positive position than previous generations of specialty coffee pros. Respected Oakland roaster Mother Tongue named their medium-dark roasted blend “Bittersweet”, and the proud specialty robusta advocate and roaster Nguyen Coffee Supply includes a tasting note of “beautiful bitterness” on its website from none other than….Drew Barrymore.

So where do we go with coffee bitterness? As robusta coffees become more popular and dark roasts become cool again, we’ll have to develop terminology around bitterness that’s more elaborate than the “dark chocolate” euphemism. Cuppers and marketers should start using “bitter” as a term, in both positive and negative ways.

And, I think it might be time to finally lose the bitterness taboo, and instead recognize that bitterness- or its absence- can both be reasonable and desirable expressions of specialty coffee flavor.

We’ve talked about the chemical origin of coffee’s aromas before: they mainly come from Maillard reactions when coffee is roasted. Compounds that are stored in the seed of the coffee fruit while the coffee plant is growing are transformed by the heat of the roaster into thousands of chemicals. But how do those chemicals get to your nose? The key is the subject I wrote about a week ago: volatility.

Here’s what happens in coffee’s case. The coffee seed (we call it a bean) is a tough little bugger, rich in lignin- which is the same thing that makes wood strong and durable. As coffee is roasted, water vapor is created from moisture in the bean, which creates pressure inside the cell walls of the coffee. The cells swell up like balloons, but the lignin fights back, resisting the steam pressure from inside the coffee. Eventually, the bean structure gives way, and the coffee bean emits a popping sound. Coffee roasters call this sound “first crack”, and it signifies the beginning of the browning stage of coffee roasting. The water vapor now gone, a new set of chemical reactions begins, called browning reactions. These reactions don’t give off water vapor, but they create another gas: carbon dioxide (CO2). The CO2 starts to puff up the cells in the same way the water vapor did, swelling the coffee cells even more. Over the course of a roast, the coffee about doubles in size from all the gas in its cells. Besides CO2, the cells contain thousands of oils, terpenes, acids, pyrazines, esters, and other chemicals, many of which are light and volatile. By the end of the roast, a coffee bean viewed through a microscope resembles a sponge, with a lattice of little chambers. These chambers are the inflated cells of the coffee seed- the walls of lignin holding in all the carbon dioxide and aromas produced during roasting.

Immediately after roasting, coffee begins to shed the CO2 produced during roasting, a process roasters call “outgassing”. But here’s what’s cool: though CO2 itself is odorless, the gas carries coffee aromatics along with it, providing a conduit for the aromatics to get into the air and into your nose. This is why coffee beans smell so powerful- their natural aroma is propelled by the CO2 gas inside its cells out into the world.

But lignin is very strong, and most of those cells remain intact, with the gas locked inside. And this is why, if we want to release the full aroma of a coffee bean, we must grind it. Grinding cuts the bean into thousands of tiny pieces, ripping apart the lignin structure, opening each one of the coffee’s cells and exposing it to air. The gases are been released, and the CO2 carries all those beautiful aromas into the sky. Fly, little aromas, fly! This is why grinding coffee just before brewing is so effective at maximizing coffee’s smell- the gases don’t have much time to dissipate, and can be dissolved into hot water during brewing.

Brewing coffee is therefore about dissolving volatile aromatics into water along with some tastes. And, since aromas, when accompanied by taste, create the perception we call “flavor”, these volatiles are a key part of coffee’s ultimate flavor profile. Aroma+taste=flavor. But hot coffee can barely hold on to some of those aromatics- they jump aboard the steam that rises from your cup, and create the delicious smell of a hot cup of coffee (see the glorious pictures from 70s coffee commercials above) This is also why cold coffee smells less intense than hot coffee does. But regardless of the temperature of the coffee when it’s sipped, it gets closer to body temperature in the mouth. By the time it’s swallowed, warm coffee vapors rise up the nasopharynx into the nasal cavity, where the aromatics can be smelled. Aroma+taste=flavor, remember?

This explains why the Coffee Taster’s Flavor Wheel is so named. Many of the attributes are primarily aromatic, but they become a part of flavor when the coffee is consumed. For this reason, almost all coffee flavors can be smelled. Floral, fruity, chocolate, brown sugar, spices…. it’s all there in those beautiful aromas that soar from the cup into the air. We train as coffee “tasters” by smelling aromatic references, because it’s largely smells that create the flavor of coffee in the first place. If you look at the categories in the center of the wheel- floral, fruity, sour/fermented, green/vegetative, roasted, spices, nutty/cocoa, and sweet, along with the precise descriptors as you move outward, you’ll realize that they are mostly aromatic descriptors. Coffee tastes sweet, sour, and bitter, but it smells like a million other things! And each of these aromas represent a little molecule that was light enough to hitch a ride on carbon dioxide or water vapor and get in to your nose. Magical.

This epiphany is so powerful to coffee people that it has led to an entire philosophy about coffee’s identity as a fruit. “Fruits are sweet,” the philosophy goes, “and that’s why coffee is sweet.”

There is a lot of truth in this, but it’s also more complicated. Let’s explore the source of sweetness in coffee.

To begin with, coffee can be sweet. Consumers and professional tasters alike detect sweetness in unsugared coffee, and value it highly when they encounter it. Evaluating sweetness has been an important part of coffee tasting protocols for decades. Roasting companies revere sweetness, celebrating its existence on their labels. There is no question that the “natural sweetness” in coffee is valuable, exciting, perceptible and very very real.

The only thing is: roasted coffee has almost no sugar. Sugars exist in the raw seed, but they are destroyed by heat, which breaks them down into various other compounds. Any residual sugars left in the roasted bean are far below the threshold of human detection and provide no calories. But it gets weirder. Studies of sweetness in coffee show that its perception is most evident when the strength of the coffee is lowest. That means that the easiest way to enhance a coffee’s natural sweetness is to make it weak and- in coffee terms- underextracted. This is the opposite of what you would expect if coffee’s sweetness came from sugars.

So what is coffee sweetness all about? Well, it’s clearly associated with the phenomenon of sweetness overperception that I wrote about here. (if you haven’t yet read that article yet, please do- it’ll help you understand this one) If sweetness perception is the human capacity to detect sugar, it is giving us a false positive in coffee’s case. But is it an illusion, really?

Well, to begin with, human perception of sweetness in coffee is reliably perceptible by tasters. Coffee experts were shown to repeatably and consistently order coffees from sweetest to least sweet. When the same tasters were asked to perform the same task with a nose clip, they can still do it, but with more difficulty. This shows that the sweetness in coffee has a strong aromatic component. But it also suggests that aroma isn’t the whole story. Coffee smells sweet, but it tastes sweet too. The same researchers are currently looking for chemical markers of sweetness in coffee, but they haven’t yet published their results. So, from a chemical perspective, we don’t yet know what causes coffee sweetness.

But our natural chemistry detectors- our senses of taste and smell- can give us clues. Let’s begin with the favorite tool of coffee tasters- the flavor wheel. Sweetness appears in three sections on the upper-right of the wheel, in the categories “sweet”, “floral”, and “fruity”.

As I previously wrote, several sweet-smelling aromatics in coffee come from browning reactions, including the Maillard reactions. Caramel, maple, molasses, and most crucially vanilla aromas are produced during browning. These compounds- known as “sweet aromatics” to coffee tasters- are critical in driving the perception of sweetness among almost everyone.

Moving clockwise around the flavor wheel, we hit the floral aromatics. Flowers can be intensely sweet-smelling: think of honeysuckle or gardenia (a botanical relative of coffee. The floral notes we encounter most in coffee are black tea, chamomile, rose and jasmine, which are all sweet in different ways.

Finally, the fruits. Fruit aromatics have been shown to be less powerful than vanilla in triggering sweetness perception, but nevertheless fruit aromatics can be a trigger of “sweet” in beverages. A good example of this is in unsweetened flavored soda waters- a passionfruit or cherry La Croix will trigger perceptions of sweetness. So it is in coffee- an aromatic note of berry or apple or peach can evoke powerful memories- and, later, perceptions, of sweetness in coffee.

So, these aromatics- perceived by the nose- can drive the sensation of sweetness. But what about tastes, perceived on the tongue? It seems likely that there are sweet-tasting nonsugar compounds in coffee- though the specific chemistry has not yet been identified, the indications seem clear that there that these sweet-tasting molecules exist. But, perhaps even more powerful is the role of bitterness. It’s long been known that bitterness and sweetness suppress each other: a bit of sugar in a bitter drink will make it seem less so, and a splash of bitters in a sweet drink will reduce the perceived sweetness. Bitterness is a common taste attribute in coffee, of course, and when it appears it will logically suppress any sense of sweetness that exists. Also, the opposite: if expected bitterness fails to appear in coffee, it may be perceived as sweetness. In this way, we can think of sweetness perception in coffee as a kind of “anti-bitterness”; an absence of bitterness in coffee may be perceived as sweetness. Indeed, in coffee studies, bitterness and sweetness seem to be powerfully inversely correlated, suggesting that an inverse relationship between the two tastes may exist.

Vanilla, sweet aromatics, fruitiness, floral, bitterness… the drivers of sweetness in coffee are many and they are complex. Perhaps this complexity explains the obsession with sweetness that many coffee people display- we love what we aspire to understand.

Tim Hill, a colleague of mine, once tried to pinpoint the moment when coffee flavor develops. While roasting coffee, he pulled a small sample from the roaster every thirty seconds during the roughly 12 minute roast. He then ground them separately, and brewed them each like you would a normal coffee. And the moment was obvious: slightly past halfway in the roast, just before the coffee undergoes the phenomenon called “first crack”, coffee begins to smell like…. coffee.

This is because of the Maillard reaction, first described by chemist and physician Louis Camille Maillard in 1912. The reaction is simply this: when certain amino acids and carbohydrates are heated together, they produce brown compounds that happen to smell amazing. I wrote recently how it is the Maillard reaction that makes French Onion Soup the most delicious broth in the world, and it is also the one that makes coffee the most delicious beverage in the world. But wait- onion soup and coffee don’t taste identical to each other; how can the same chemical reaction be at work? Well, we should really think of Maillard reactions in the plural- multiple carbohydrates can react with various amino acids to create a huge variety of compounds- literally hundreds of different aromatics. But they generally tend to be brown, and they generally smell delicious.

Green coffee’s amino acids include alanine and asparagine, and carbohydrates include sucrose and other sugars. These compounds- and others- break down and start reacting in complex ways, producing what are known as Maillard Reaction Products (MRPs). It’s these MRPs that create most of the aromatics that we enjoy in coffee. MRPs are why coffee can smell like butter or chocolate, like nuts or toast.

Maillard reactions begin to happen most abundantly at temperatures between 280 to 330 degrees Fahrenheit (140 to 165 degrees Celsius). During coffee roasting, that’s a little past halfway through the roast, just before the beans begin to crackle. Flavors continue to evolve right up until the end of the roast, however. (It’s no coincidence that ovens and coffee roasters alike tend to operate in the 350-500 degree Fahrenheit zone- that’s the place that Maillard reactions can really flourish).

In coffee tasting terms, the Maillard Reaction flavors are most evident on the left side of the Coffee Taster’s Flavor Wheel, roughly between 8 and 12 o’clock. You’ll notice that most of these flavors are colored brown- that’s no accident: this is browning-reaction country.

At the top you’ll notice the most compelling of all the Maillard aromas- vanilla and vanillin. Scientists have called the chemical vanillin the world’s most beloved smell, and I have to agree: I use vanilla extract like it’s going out of style, and when I find it in coffee, I get chills, it’s that good. There is a long tradition of adding vanilla flavor to coffee drinks, but when it occurs naturally through the roasting process, it’s especially compelling.

Moving counter-clockwise through the flavors brings us to the brown sugar flavors. Now, the smell of brown sugar can also come from a separate, distinct browning reaction called “caramelization” that does not require amino acids, but Maillard reaction aromas can include the smells of maple syrup, honey, and molasses.

Next up, chocolate. Chocolate is a lovely example of a Maillard flavor, and is of course present in the roasted seeds of the cacao plant. But we can detect chocolate and cocoa flavors elsewhere too- roasted carob, barley, and even toasted marshmallow can smell like chocolate sometimes, as can coffee. 2-Methylfuran is a well known Maillard product that smells like chocolate.

The nuts are next on our tour of the brown part of the flavor wheel: almond, hazelnut, and peanut. This is at least in part related to 2,6 dimethylpyrazine, a MRP with a famously nutty aroma. Roasted nuts themselves have Maillard reaction products, so it’s no accident we detect nutty aromas in coffee.

The “brown” spices clove, cinnamon, nutmeg and anise have a distinct set of aromas that can result from Maillard reactions. One of the MRPs connected with this is guaiacol, an aromatic compound present in coffee that has a spicy, clove-like scent.

Probably the most recognizable Maillard flavors of them all are the ones associated with toasted grains. Malt, a term for toasted germinated barley, and cereals are- along with bread- some of the most classic of the browning reaction flavors. In fact, toasted grains have been used as coffee substitutes for hundreds of years, due solely to the commonality of Maillard reaction flavors between the two. And, though less familiar to people today given the decline of tobacco use, the scent of pipe tobacco flavors exist in coffee too.

But there is one very important Maillard reaction flavor that is omitted from the flavor wheel, and it may be the best one of them all. It is…. (checks notes)…... coffee. Many of the chemicals produced by the Maillard reaction are recognizable as coffee itself.

In short, it is no exaggeration to say that the Maillard reactions are the very core of coffee flavor. Coffee is Maillard and Maillard is coffee. No wonder I love them both so much.

But that’s not the only confusing thing: sourness is a polarizing taste. We love sour foods- from citrus fruits to pickles to grapes. But too much sour turns us off. Flavor scientists refer to this as an “inverse U-shaped hedonic response” which is to say we like a little sourness more than no sourness, but too much sourness and we hate it. And this is exactly the case with coffee: the right amount of sourness makes coffee taste delicious and mouthwatering, balancing out coffee’s inherent bitterness and enhancing its natural sweetness. A coffee without acid tastes drab and lifeless, ashy and hollow. But a twinge of acidity- just enough- brings a coffee to life and makes it compelling and delicious. So, in coffee, “sour” in coffee is when there is too much or unpleasant sourness, “acidity” is when there is a good, balanced, pleasant sourness.

For these reasons, “acidity” has been a term used by coffee experts for over a hundred years. Certain coffees- like coffees from Kenya and Costa Rica- are thought of as having an especially pleasant and intense acidity. Lots of processing and agricultural factors seem to influence acidity in coffee, which is one reason why coffee buyers obsess about these details. There is a whole section on the Coffee Taster’s Flavor Wheel dedicated to acids and sourness- right there next to the citrus fruits. But what about coffee drinkers? The inverse u-shaped response also explains why coffee buyers fetishize acidity in coffee but consumers avoid it- they are talking about different things. Coffee people are talking about a moderate, balanced acidity- they sometimes call it “sweet acidity”- that brings coffee to life. Consumers are talking about sourness- which they associate with fruit juices and vinegar. Different things.

Ok, let’s talk chemistry. Sourness and acidity come from acids, and like many plants, coffee has several acids stored up in its tissues. For convenience, we can divide them into two categories, organic acids and chlorogenic acids. Organic acids seem to have a more powerful effect on flavor than chlorogenic ones, so we’ll focus on those. Of the organic acids, citric and malic acids are the most important ones in coffee. There is a persistent myth that citric acid tastes like citrus and malic acid tastes like green apples, but in truth they are hard to distinguish from one another: they both taste just sour. And, coffee tasters can’t distinguish between them in coffee anyway. Other acids exist, but mostly seem to play a supporting role (one of these is acetic acid, which is a special case I’ll discuss elsewhere). Both citric and malic acids degrade during roasting, which is why light roasted coffee tastes more sour than dark roasted coffee. Acidity is one of the important tastes that roasters control- a little extra roasting will temper the acidity in a coffee, but too much roasting will extinguish it, leaving the coffee flat and ashy tasting. For this reason, many roasters who like to roast dark buy coffees that are extremely high in acidity in the first place- then they can roast dark and still have a little bit of sparkle in the cup.

All of this talk of chemistry might make you want to whip out your pH meter and start measuring your coffee’s acidity to predict how it will taste. Well, funny thing: it turns out that just measuring the pH of a coffee will tell you little about its flavor. This is true in wine and other foods as well, which is why there is another measure of acidity used for foods, called titratable acidity. Instead of measuring hydrogen ions as pH does, titratable acidity (TA) measures how much of a substance needed to neutralize a certain amount of a base. TA is a much stronger predictor of sourness in foods and beverages than pH, but it’s still not perfect. That means other factors are at work in coffee to make it taste more or less sour- perhaps the coffee’s bitterness is amplifying the perception of sourness, or the sweetness is muting it. Aromas can play a role too- fruity aromas might increase the perception of sourness in coffee. All this means that a coffee’s measured acidity (its pH or TA) might not be the same as its perceived acidity (sourness). From here on out, I’ll try to be specific when I talk about the two.

So, as a coffee drinker, how do you optimize the perceived acidity you like in a coffee? First, learn to recognize it: if you drink a coffee and you feel a pleasant tang, or mouthwatering sensation, that’s perceived acidity. High perceived acidity might taste sour, like in a very light roasted espresso. If you taste fruit, there is a good chance you’re tasting acidity too. Lower-acid coffees tend to taste nutty, or like cocoa powder. Both can be delicious. Brewing can modulate acidity too- using a higher coffee- to- water ratio has been shown to increase sour tastes in coffee. Cold brewing has been shown to reduce acidity in coffee too.

If you want to explore acidity in coffee, here are some tips: since perceived acidity lessens during roasting, light roasted coffees tend to have much higher perceived acidity than dark roasts. Coffees from Kenya, Ethiopia, and some places in Central America will tend to have high acidity. Look for terms like “bright”, “crisp”, and “citrusy” on the label.

If you want to taste lower acid coffees, try darker roasts- the roasting minimizes much of the perceived acidity in the coffee. Coffees from Indonesia, especially Sumatra, are well known for having gentler acidity, as do many coffees from Brazil. Look for terms like “nutty”, “chocolatey”, and “spice”- they often accompany lower-acidity coffees.

So, though acidity is an essential and desirable flavor characteristic in coffee, in excess it can turn people off. And because taste is personal, that place is likely to be in different places for different people. I happen to love intense acidity in coffee- I find it cleansing and exciting- but I know and respect lots of coffee drinkers who favor milder, less-acidic tastes. Now, go drink some coffee!

p.s. In my view, the perfect and best representation of acidity in coffee is in iced coffee, my favorite summertime drink. A crisp and bright acidity in cold coffee does exactly the same thing that acid does to water- it makes it more refreshing, thirst-quenching, and satisfying on a warm day. That’s why I you will find me drinking washed Ethiopian and Kenyan coffees, served cold over ice, between May and September every year.

p.p.s. You’ll notice I did not mention anything about the relationship between coffee acidity and gastric discomfort, which has been a hot topic (no pun intended) in coffee. This is very intentional. I am not an expert on coffee and health issues, so I generally try to scrupulously avoid discussing the health implications of coffee. I will say that, in my reading, the evidence linking coffee and gastric distress just isn’t there. But that’s not uncommon for dietary studies- it’s very very difficult to study the effects of foods on the health of human subjects. I believe people who report gastric distress after drinking coffee, but neither the effect nor the cause seems to have been demonstrated very well. I always give the same advice to people who ask me: listen to your body, and try a variety of coffees in the marketplace- some are designed to offer better compatibility to those with sensitive stomachs. If low-acid coffee works for you, by all means drink it!

p.p.p.s. For coffee science geeks, please do check out the papers linked in this post. While writing, I was reminded of the amazing work coffee scientists have been doing- most within the past 5 years- on coffee acidity.

Demeter and her daughter Persephone give the gift of barley to the world, a central theme of the Eleusinian mysteries. Is that kykeon in the jar?

The Eleusinian mysteries were observed for hundreds of years, and during the Roman period the rituals became popular among Roman elites. And the consumption of (non-psychedelic) kykeon became popular among the Romans too. As the drink’s popularity grew, the Romans gave it a new name, after their word for barley, hordeum. They called barley-water hordeata.

Just as in Greece, Roman hordeata was extremely common among all classes. Barley-water is economical as well as refreshing; you can boil the barley, using the boiled grains to eat and the barley water to drink. In addition to flavoring hordeata with herbs, Romans began adding spices and almonds to the brew. Almonds contribute milkiness, sweetness and flavor to hordeata, in addition to being a good source of creamy fat.

Hordeata spread wherever the Romans went, from Roman Britain to France and Spain. And in all of these places, it changed names and recipes. In Britain, the almonds never caught on, but the drinking of barley-water did: it is a beloved summertime tradition, and the Robinsons brand makes a popular bottled version. In Italy, almonds ended up dominating the flavor profile of hordeata, and the drink became called orzata in modern Italian. Today, though Italian orzata can be made with barley, it’s more often made from a syrup of almonds and sugar, sometimes flavored with lemon. This is the drink that became popular in France, where it is called orgeat, and often contains a dash of orange blossom. In Spain, hordeata became horchata, and encountered a new ingredient: a nutlike tuber called chufa, imported from Africa. Chufas make delicious horchata, and the Spanish substituted them for almonds and barley, adding a bit of cinnamon to the refreshing, creamy drink, called horchata de chufa.

The spread of barley-water from Greece to Europe and beyond

The desire for horchata de chufa accompanied the Spanish colonists to the new world, but chufas never quite caught on in the colonies. However, a new basic grain did: the Asian staple, rice. Rice was imported by the Spanish conquistadors in the 16^th century from both Europe and the Philippines, and at some point Mexican cooks realized that rice makes a delicious version of Spanish horchata. The cinnamon flavor stuck, and Mexican rice-based horchata became included in the pantheon of aguas frescas, the delicious, flavored waters of Mexican cuisine.

Aguas frescas in Juchitán de Zaragoza, with horchata on the right. photo Gzzzz, creative commons

Since the 1960s, Mexican food has enjoyed growing popularity in the US and abroad. Tacos, taquerias and taco trucks are universally beloved, and regional specialties like birria have become on-trend dishes among foodies and the general public alike. Horchata has ridden this wave of Mexican-food popularity, and over the past several years the beverage has broken out of the taco shop and into the American mainstream. One can get Mexican-style horchata at convenience stores and upscale restaurants; stores offer horchata-flavored ice cream, donuts, and cocktails. Horchata’s creamy sweetness makes it an ideal complement for coffee; nobody knows who first had the idea to combine the two. However, when LA’s Tierra Mia coffee opened their first shop in 2008, the Horchata Latte- a mixture of espresso and steamed horchata- was on the menu. Since then, horchata-based coffee beverages have been proliferating throughout the west coast- from Contra Coffee’s “Dirty Horchata” to the Black Rice Horchata Latte of Santa Ana’s Café Cultura.

Horchata latte at El Mitote Cafe, Ukiah, California by Sarah Stierch (CC BY 4.0)

And we owe these coffeeshop specialties to ancient Greek goddess worship, the expansion of the Roman empire, the Spanish conquest of Mexico, and the delicious greatness of the taco shop.