Flavor is the main aspect of any particular beer that distinguishes it from others and one of the major reasons we drink the beers we enjoy. It is also, perhaps, the aspect of beer that has changed the most drastically in the modern age. Technically speaking, most of what we think of as a sense of taste is actually more accurately described as a sense of smell. The overall sensation we think of as “flavor” is a blend between sensory input from the olfactory system and input from the tongue and mouth. The olfactory bulb, located at the peak of the nasal cavity, is studded with thousands of receptor cells, each of these tuned to a particular range of aroma-active molecules that are vaporized into the air. The mouth is linked to the nasal cavity by the retronasal passage, allowing us to fully “taste” food and drink when it is in our mouths rather than only when it is in front of us. More than 1,000 genes, a full 3% of the total number in humans, are devoted to our sense of smell. See aroma.

Our sense of taste is a far blunter instrument. Humans have about 10,000 taste buds, mostly on the tongue but also scattered within the soft and hard palate, the cheeks, and the lips. Whereas many animals, for example, dogs and cats, have olfactory senses far superior to that of humans, human taste mechanisms are particularly well developed when compared with those of our pets. The palate and the tongue’s taste buds only perceive several sensations—sweet, salty, bitter, acid, and the so-called fifth taste, umami, the flavor of glutamates. Recent research suggests that taste buds also perceive fat, but this appears unproven, and because beer contains no fat, we will not address that theory here. See umami.

Sweetness seems very clear to us, and it is perhaps our earliest memory of flavor. If one thinks of childhood, sweetness pops to mind far faster than saltiness or sourness. The human brain is wired to like sweet things, perhaps because of their high caloric value. Unlike wine, beer almost always contains residual sugars, even if the beer does not taste sweet. Sweet elements derived from malt will be balanced against the hop bitterness, roast bitterness, carbonation, and possible acidity in a beer. Not many beer styles contain notable amounts of residual sugar, and sweetness rarely dominates the palate of beer. However, some stronger styles, such as barley wines, doppelbocks, and Scotch ales, often have semisweet flavor profiles. The sensation of sweetness is more complex than the presence of sugar itself, because other compounds can trigger sensations of sweetness. Alcohol, for example, can seem sweet; stronger beers may seem to be sweet at first, even when residual sugar content is low. Various esters, which the olfactory system will sense as fruity aromatics, will enhance perceptions of sweetness. The brain can combine sensations of actual sugar, alcohol, and esters into a single complex impression of sweetness. Unlike other types of sweetness, actual residual sugar lingers on the palate after beer is swallowed.

Bitterness is the backbone of the flavor of most beer flavor, providing the counterpoint to malt sweetness. Bitterness is derived from various acids in hops, but roasted malts can provide a different type of bitterness as well. Hop bitterness and roast bitterness in beer will intensify each other. Our relationship with bitterness is complicated, cultural, and changeable. In the plant world, bitterness is often a sign of poison, and bitter flavors protect many plants from being eaten by animals. Most humans are able to turn off this “alarm signal,” but this differs from culture to culture. For example, Italian food and drink culture seems to be in love with bitterness, as represented by a huge range of popular Italian bitter liqueurs, biting espresso coffee, and the popularity of vegetables such as broccoli rabe and radicchio in Italy. Americans, on the other hand, appear to be less enamored of bitter sensations and are better known for having a national sweet tooth. However, the recently developing popularity of bitter craft brewed beers may signal the start of a change in the American culture of flavor.

There are many qualities of bitterness in beer, just as there are differing qualities of red wine tannins. Bitterness may be quick and snappy, seeming to fade after a few sips, or it may slowly gather and rise as a beer is consumed. Different hops give different types of bitterness, a fact that is empirically observed, but imperfectly understood. Brewers will study analyses of hop varieties, looking for clues to bitterness quality and seeking to create the type and intensity of bitterness they want in their beers. See bitterness.

Although individuals differ, studies show that women tend to have more taste buds than men and that they are more likely than men to be “supertasters,” people with acute sensitivity to flavor sensations. This may explain why fewer women than men enjoy bitter beers, especially if this is tied to the evolutionary advantages of having females avoid foods that send bitter warning signals to the brain.

Our perception of saltiness is tied to concentrations of sodium, potassium, calcium, and magnesium ions in our food and drink. In beer, salts will naturally come from brewing water, although brewers may also add them to influence beer flavor. Beers rarely actually taste salty, but a slight sensation of salinity is not uncommon. When added to brewing water in small amounts, sodium chloride can enhance beer flavor, giving a sense of greater palate fullness.

All beer is essentially acidic in nature, with most having a pH between 4.1 and 4.5. However, noticeable acidity is not a major factor in the flavor of most beers. From the dawn of civilization, beer was spontaneously fermented by wild yeasts and bacteria, and acidity was once one of the most prominent flavors in beer. Today, acidity is only assertive in a few beer types, including lambics and fruit beers. Among craft brewers there is a rising interest in acidity, and many look to lambic as an inspiration for the creation of intentionally sour beers. See lambic and sour beer.

Umami, which is Japanese for deliciousness, is the flavor of glutamate compounds, amino acids that form proteins. It is also given by ribonucleotide substances, which are known as powerful flavor enhancers, especially when combined with glutamates. Umami describes flavors underlying those of gamey meat, sea urchin, seaweed, soy sauce, fermented fish sauces, Marmite, mushrooms, ripe tomatoes, and many cheeses, especially Parmigiano–Reggiano, which contains up to 12% glutamate by weight. In beer, meat-like umami flavor is usually considered a fault because it is indicative of unwanted yeast autolysis and breakdown. However, it is a normal part of the flavor profile of beers that are intentionally aged, especially if they are aged on yeast. Here, it often comes across as “toasty” and can come to resemble the “sur lie” (on sediment) character prized in vintage Champagne. In such aged beers, umami can be a powerful factor in the creation of pleasant food pairings, particularly with foods that contain their own umami character. See aging of beer and autolysis.

Aside from these five basic flavors, there are other sensations in beer as well. The fizziness of carbonation is both a tactile sensation and a chemical taste sensation (a form of acidity)—the brain combines these to create the “tickle” or “burn” we associate with carbonation. Temperature is critically important to the flavor of beer, and both the palate and the olfactory sense will perceive beer very differently at varying temperatures. Finally, we have the trigeminal reception system, which perceives actual temperature, but also flavor-based sensations such as cooling (mint, anise), burning (chili peppers, alcohol), and numbing (menthol, Roquefort cheese). Astringency is technically not a flavor, but a tactile/trigeminal sensation. That said, we surely perceive astringency as part of flavor. The trigeminal system also senses viscosity—whether a beer “feels” round, soft, or silky or, alternatively, thin and watery.

Flavors not only combine with aroma and trigeminal responses but are also affected by flavors that were previously on the palate. For example, drinking a full-bodied sweet barley wine can give difficulty to other beers served after it, making them taste drier, thinner, and harsher. It is therefore important for trained tasters to pay attention to the order in which beers are tasted, served at the table, or judged. Even our sense of sight affects our sense of flavor, a fact well known to food technologists whose job it is to make commercial foods preparations look appealing to consumers. This effect appears to be linked to the cognitive expectations we associate with color. If a beer looks dark, it tends to “taste” heavier and richer; if it is amber, we look for notes of caramel.

When we drink beer, all of these many aspects combine to create the overall impression we commonly call flavor. Beyond these factors lie our psychological and emotional states, our personal memories, and the environment within which we are drinking. No beer truly tastes the same at the brewery as it does in a pub suffused by the warmth of friends and the smells of perfume and food. Nor will a beer taste the same on a fishing boat as it does in front of a fireplace. Some parts of beer flavor will be measurable and others will not. For those of us who do not analyze beer for a living, perhaps any analysis of beer flavor should largely be a matter of personal enjoyment and the provision of good hospitality.