Understanding (and appreciating) Bitterness in Coffee
Is bitterness in coffee good or bad? Is it a feature or bug? And, is bitterness in coffee making a comeback?
Earlier this week, I wrote about the Italian culture’s relationship with bitterness in foods and drinks. And, of course, the Italian relationship with bitter is closely tied with its attitude towards coffee. The circumstance calls for an exploration of bitterness in coffee. It might help to read that article first, but I’ll try and cover the fundamentals of bitterness here too.
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.
Beautiful
Great thoughts! By the way, I love your texts, mainly the coffee ones.