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Bitterness: the chemistry of bitter taste in coffee, tea, beer and wine

Bitterness is a taste that links four of the most popular drinks in the world: coffee, tea, beer and wine. It is what gives IPA its characteristic bite, espresso its depth, strong tea its vividness, and red wine its structure. Interestingly, although the effect is sometimes similar, the sources of bitterness in each of these drinks are completely different: from hop iso-alpha-acids, through caffeine, to catechins and polyphenols. Understanding the chemistry of bitter taste reveals the fascinating kinship and differences of these drinks. In this cross-niche post we will look at bitterness in coffee, tea, beer and wine: you will learn its sources, the difference between bitterness and astringency and how to come to love this at-first difficult taste. It is a journey through the bitter taste that links four different drinks with a shared, though manifold, language.

Bitterness - one of the basic tastes

Bitterness is one of the five basic tastes, alongside sweet, sour, salty and umami, detected by special taste receptors on the tongue. Unlike astringency, which is a tactile sensation, bitterness is a true taste. It is a taste that evolutionarily served as a warning against potentially poisonous substances, which is why many people initially react to it with aversion. And yet in drinks bitterness is often valued, and even sought: it gives them character, depth and balance. Without bitterness IPA would be bland, espresso flat, and strong tea expressionless. Fascinatingly, although bitterness in coffee, tea, beer and wine gives a similar sensation, its chemical sources are different in each drink. Understanding that bitterness is a basic taste of different sources is the key to this post. It is a taste that divides and links: it divides into those who like it and those who do not, and links four drinks with a shared sensation. So let us get to know where exactly the bitterness in each of them comes from.

Why we feel bitterness at all

To understand bitterness, it is worth knowing why we feel it at all. Bitterness is detected by special bitter taste receptors on the tongue, of which humans have relatively many. This is not accidental: over the course of evolution the ability to detect bitterness protected us from eating poisonous plants, because many toxins are bitter. That is why bitterness is for the body a warning signal, and many children and adults instinctively avoid it. This explains why bitter drinks, like black coffee or strong IPA, are often an acquired taste that has to be learned. Over time, however, we learn to appreciate bitterness, and even to seek it, because in the right dose it adds complexity and a pleasant balance to drinks. The same sensitivity to bitterness that once protected us from poisons today lets us enjoy bitter drinks. Understanding the evolutionary background of bitterness explains why it can be difficult, and at the same time why it can be learned to love. It is a taste that requires getting used to, but rewards those who open up. Let us now get to know its sources in four drinks.

Bitterness in beer

Beer is the drink in which bitterness is most consciously controlled and valued, and its source is well known: hops. The main source of beer’s bitterness is iso-alpha-acids, forming from the alpha acids of hops during the boil of the wort. Alpha acids, like humulone and related compounds, are themselves poorly soluble, but during the boil they isomerise, that is transform into soluble iso-alpha-acids, which give beer its characteristic bitterness. That is why beer’s bitterness is measured in IBU units, reflecting the content of these compounds. The longer and more hops are boiled in the wort, the more iso-alpha-acids and the more bitter the beer. The bitterness of hops balances the sweetness of the malt, giving a drinkable, balanced beer. It is in beer that bitterness is most intentional, and brewers dose it precisely. Besides hops, a slight bitterness and astringency are also given by tannins from malt and hops. Hop bitterness is the calling card of styles such as IPA. We write more about hops in our post on why IPA tastes like grapefruit.

Bitterness in coffee

Coffee is the drink associated with bitterness perhaps most strongly, though its sources are more complex than in beer. Caffeine, which is bitter, is partly responsible for it, but it is not the main culprit. A greater role is played by compounds forming from chlorogenic acids during roasting, especially the products of their breakdown. That is why dark-roasted coffee is far more bitter than light-roasted: the longer and more strongly the bean is roasted, the more bitter compounds form. The bitterness of coffee thus strongly depends on the degree of roast. An additional source of unpleasant bitterness is sometimes over-extraction, that is too long or too hot brewing, which draws out an excess of bitter compounds. Well-balanced coffee has a moderate bitterness, balanced by acidity and sweetness. That is why control of roasting and brewing is key for flavour. Bitterness in coffee is the sum of caffeine, compounds from roasting and extraction. Understanding its sources helps brew better, less bitter coffee. We write more about coffee flavours in our post on coffee acidity.

Bitterness in tea

Tea is the drink in which bitterness and astringency usually go together, and their main source is catechins. They are a group of polyphenols, especially abundant in green tea, which bring both bitterness and a puckering astringency and structure. Catechins have even been assessed for bitterness using studies with human bitter taste receptors. Alongside catechins, some bitterness is also given by the caffeine present in tea. The key is that the bitterness of tea strongly depends on brewing: water that is too hot and a steeping time that is too long draw out an excess of catechins and caffeine, making the brew bitter and unpleasantly astringent. That is why delicate green teas are brewed with cooler water and for a shorter time. Well-brewed tea has a moderate and balanced bitterness. Bitterness in tea is thus mainly the work of catechins, controlled by the way of brewing. Understanding this explains why the same tea can be pleasant or as bitter as medicine. We write more about this in our post on why your tea tastes bitter.

Bitterness in wine

Wine is the drink in which bitterness is subtler and often intertwines with astringency, and its source is polyphenols, mainly tannins and catechins. Tannins, coming from the skins, seeds of grapes and from oak casks, give wine not only puckering astringency, but also a certain bitterness and structure. The concentration of catechins and pH affect the sourness and bitterness of wine. Bitterness in wine is usually less prominent than in coffee or beer, because it is balanced by fruitiness, acidity and sweetness. In young, strongly tannic red wines the bitter-astringent character can be clearer, but with age it softens, as the tannins smooth out. Excessive bitterness in wine, for example from an excess of oak or unripe seeds, is sometimes considered a fault. Well-balanced wine has a discreet bitterness, woven into the whole. Bitterness in wine is thus mainly the work of polyphenols, closely linked with astringency. Understanding its sources connects with the topic of tannins. We write more about this in our post on tannins in drinks.

Bitterness versus astringency

An important, often confused distinction is the difference between bitterness and astringency. Bitterness is a basic taste, detected by receptors on the tongue. Astringency, that is the puckering, dry sensation in the mouth, resulting from the binding of saliva proteins by tannins, is a tactile sensation. These are two different things, though they often occur together and are sometimes confused. Many compounds, like catechins in tea or tannins in wine, give both sensations at once: both bitterness and astringency. That is why strong tea is sometimes both bitter and puckering. But it is not the same. Bitterness we feel as a taste, astringency as a physical sensation of roughness. Distinguishing these two is key in tasting: it lets you describe more precisely what you feel and understand where it comes from. In coffee and beer rather pure bitterness dominates, in wine and tea it more often mixes with astringency. Understanding this difference orders the impressions and helps assess drinks more consciously. They are two related, yet distinct aspects of flavour, worth being able to tell apart.

Sources of bitterness in brief

Let us gather the sources of bitterness in four drinks, to see how different compounds give a similar sensation:

The table shows a fascinating thing: the same, basic bitterness in each drink comes from completely different compounds. In beer it is hop iso-alpha-acids, in coffee the products of roasting and caffeine, in tea catechins, in wine tannins. Despite the different sources, the effect on the tongue is related. It is proof of how different chemical routes lead to the same taste.

How to come to love bitterness

Bitterness can be difficult at first, but it can be learned and appreciated. First, gradual familiarisation helps: the more often we drink bitter drinks, the more we get used to bitterness and begin to like it, because it is largely an acquired taste. Second, the key is balance: bitterness tastes best balanced by sweetness, acidity or fat, which is why bitter coffee with a little milk, dark chocolate or IPA with fatty food become more pleasant. Third, dose control: in drinks we brew ourselves, like coffee and tea, proper extraction lets you avoid excessive, unpleasant bitterness. Fourth, combining with food: bitter drinks go superbly with fatty, sweet or salty dishes, which soften the bitterness. Fifth, patience: appreciating bitterness is often a matter of time and exposure. Over time what was once off-putting becomes desirable. Coming to love bitterness opens the door to the fullness of flavour of coffee, tea, beer and wine. It is a taste that rewards those who give it a chance.

Why we like bitter

Since bitterness is an evolutionary warning signal, why did we learn to like it at all, and even seek it? There are several reasons. First, bitterness in drinks usually does not signal a real threat, so over time the brain learns that it is safe, and even pleasant. Second, bitterness adds complexity and depth to drinks, balancing sweetness and making the flavour more interesting, less flat. Third, bitter drinks are often linked with stimulation, like caffeine in coffee and tea or alcohol, which strengthens their appeal. Fourth, culture and context: appreciating bitter drinks is sometimes a sign of a developed taste and adulthood. Over time bitterness becomes not a fault, but a desired trait, adding character. It is a fascinating example of how a taste initially rejected evolutionarily becomes a favourite element of drinking culture. Liking bitterness is the triumph of acquired taste over instinct. For the connoisseur bitterness is not something to tolerate, but an integral, valued part of the experience of coffee, tea, beer and wine. It is a mature taste, the appreciation of which testifies to an open, developed palate.

The key points in a nutshell

Bitterness is one of the basic tastes, detected by receptors on the tongue, evolutionarily warning against poisons, which is why it is often an acquired taste. It links four drinks, but its sources differ: in beer it is iso-alpha-acids from hops, measured in IBU; in coffee compounds forming during roasting and caffeine; in tea catechins and caffeine; in wine tannins and polyphenols. Bitterness is a taste, different from astringency, which is a tactile sensation, although they often occur together. Bitterness can be learned to love through gradual familiarisation, balance with sweetness and acidity, control of extraction and combining with food. Over time it becomes a valued trait of drinks. Want to compare bitterness in different drinks and record your impressions? Keep notes in the GustoNote app. See also our posts on tea bitterness and tannins in drinks.