But you like drinking one more than the other. So, you might simply order the one you prefer and leave it at that―which is how most of us experience beer. But if a friend asked you which beer to order, could you tell your friend why you prefer the beer you do?

“It tastes better. It’s very easy to drink,” you say. That’s a start, but not very persuasive.

You dig deeper. “I like the way each sip is a little bit sweet at first, but then slowly turns bitter.” But is it sweet like maple syrup or sweet like fresh peas? Bitter like broccoli or bitter like quinine?

You try comparing the beers. The one you like tastes more, well, floral than the other one. Floral? Roses or geraniums? asks your friend. “Neither. More like the smell in a florist’s shop,” you answer.

And there you are, describing a beer that tastes the way a flower shop smells. What’s remarkable is that your friend knows exactly what you’re talking about.

“I hate that flavor,” the friend says, and orders the other IPA.

The Puzzle of Flavor

You have just put your impression of that IPA into words, and you’ve done it by referring to an experience that has nothing to do with beer. And even though you and your friend disagree on how you feel about that reference―you like a very floral IPA and your friend doesn’t―you’ve helped him to select a beer he’s more likely to enjoy.

Certainly, we can express whether or not a food or beverage is pleasant without words―we can smile, or we can we push it away, or twist our faces in revulsion. But, unlike other species, we can also convey both how pleasant or unpleasant we find these experiences and why through the use of language. We generally do this by analogy, summoning memories of flavors that we all share. It’s not for nothing that we jokingly say that any bizarre new meat “tastes like chicken.”

We humans actually rely far more on our senses of vision and hearing than most other species. However, the senses of taste and smell are most vividly linked to memories and emotions.

Our other senses may have warned our ancestors “There’s a lion on the next ridge” (sight), or “A leopard just snapped a twig in that thicket” (sound). But nothing else conveys the up-close message “Don’t eat that! It’ll kill you!” with the urgency of smell or taste. You instantly relive bad experiences, you recoil, you gag―and these two most intimate senses may have saved your life.

Taste and smell also steer us towards food and drink that is full of the good stuff: sugar, fat, salt―nutrients that would have been rare in our ancestors’ landscape. They survived by following the cues of their senses, and loading up on rich foods whenever they came upon them. But in our modern environment, surrounded by plenty, our health will suffer if we let our taste buds rule.

The fascinating thing is that our taste preferences are adaptable. We may be hard-wired to eat as much as possible of any food that tastes sweet, but we learn to moderate that urge.

We are also able to reinterpret the negative messages that taste and smell convey. Take our fondness for increasingly bitter beers, for example: in nature, bitterness is usually a cue to avoid a food or drink that might harm us, but legions of beer drinker have cultivated a preference for extreme bitterness, against the bidding of their taste buds.

Our ability to perceive flavor is an essential survival skill―determined by our biology, shaped by our evolutionary history, modified by culture and experience, and expressed through strong individual preference. At the end of this long process, you, as it turns out, prefer a floral, hoppy IPA.

Taste Perception

Remember that map of the tongue that illustrated specialized areas to detect each of the four basic flavors―sweet and salt on the tip of the tongue, sour on the sides, and bitterness on the back? Now, forget the map: although it’s still repeated in lessons and textbooks, it’s wrong. It turns out that all the basic flavors can be sensed anywhere across the tongue (though perhaps in different intensities).

There are thousands of minute, mushroom-shaped taste buds on the human tongue. Molecules and ions in solution in the mouth enter the taste buds. Only in the last decade or so have researchers identified receptor cells, 50 to 100 within each taste bud, that respond specifically to each of the basic flavors, sending messages along sensory nerves to the brain―this is the mechanism of taste (or gustation).

There are now thought to be at least five basic tastes: the old foursome of salt, sweet, bitter, and sour, plus the new addition, umami―the sensation we’d describe as “meaty,” a quality also found in cheese, soy sauce or tomatoes.

Susan Schiffman, formerly of Duke University, and now a consultant specializing in taste and smell, is convinced there are even more basic tastes yet to be discovered.

“Metallic, for example,” she says. “You know certain beers have a metallic taste to them? That’s a distinct taste.” She also has experimental data suggesting that calcium salts are a separate taste: “They have a very strange taste to them that’s not sweet, sour, salty or bitter.”

And while astringency is definitely a feeling―the dry, wooly texture in the mouth―it may also qualify as a separate basic taste, and the same may be true of carbonation. In her research, Schiffman has determined that human patients who have lost the ability to feel astringency or carbonation on the tongue can still distinguish astringent or carbonated compounds through the taste buds alone.

As to whether fat is a basic sense, as some writers posit, Schiffman is doubtful. “I don’t believe it exists,” she says.

When you take a sip of beer, how does your brain process the information it gets from your taste buds? Reading just the basic tastes, does the brain register the beer as scoring, say, 15 for bitterness, zero for salt, eight for sweetness, one for sour and two for umami? Is the brain like a painter working with only a few basic colors, but employing them in a near-infinite number of combinations and strengths?

“That’s one of the theories,” says Schiffman, “that you get a continuum. I would say that’s one of the big fights in the taste field, but I would be on the continuum side.

Three different cranial nerves receive stimulation from taste buds located on different parts of the tongue: the first two-thirds, the back of the tongue, and in the throat. So your experience of a beer really does have a beginning, a middle and an end―yes, there is such a sensation as “finish” in a beer’s flavor, and beer reviewers are smart to swallow, not spit, like their wine colleagues.

What’s more, taste buds at the back of the throat can be stimulated by compounds that enter the nose and reach the back of the tongue where the nasal passage joins the throat. This means that we know something about the taste of everything we smell. When beer reviews suggest that a beer tastes of things you’d never dream of putting in your mouth―wet rocks, horse blanket, and (heaven forbid) cat box―don’t laugh: we’ve all “tasted” these compounds, because we’ve smelled them.

Of course, the tongue is also the source of valuable tactile information about a food or beverage: it detects viscosity, texture, pain and temperature―as well as giving additional cues about the feelings of astringency and carbonation.

How Do You Smell?

The sense of smell (olfaction) is far more complex than the sense of taste.

In contrast to the palette of five (or more) basic tastes, the human nose contains specific receptors for detecting hundreds of different odor molecules. “Perfumers will say they can distinguish among 10,000 different odors,” says Schiffman. “Again, I believe you have the same thing you have with taste, a continuum―it’s the relative amount of firing across different receptor types that gives you a certain experience. The pattern across these different types of receptors gives us the aroma.”

When you drink a beer, the sense of smell plays two roles: on inhalation through the nose, we detect the beer’s aroma. But when we exhale, airborne odor molecules from our mouth pass back through the nose, and contribute to our perception of taste. Your experience of flavor depends a lot on your nose: if you doubt that, think of how flat everything tastes when you have a bad cold.

Like taste, smell is modified by experience and culture. The odor of cheese is mouth-watering to many Westerners, but repulsive to many Asians, who associate the sharp, acidic smell with spoilage and sickness.

With a quick snap of my wrist and a snake-like hiss, the ale obediently slid into my waiting glass. No innocent nymph, this beery banshee fairly shrieked with a chemical so vile, so repulsive as to be pure evil. It was my old nemesis, Phenol.

My anguished cry reverberated throughout the ancient stone grotto, “Whyyyyyyyyyyyyy?”

If something like this—perhaps a bit less Poe-like—has ever happened to you, read on.

Like other metaphysical dimensions of the universe, beer making sometimes shows a darker side. Errors in brewing, biological contamination, and poor storage conditions all may contribute off flavors and aromas to beer. There are a number of fairly common characteristics whose presence is often diagnostic of specific problems.

Learning to recognize the signs of bad beer can be crucial to preventing problems in the future, but more than that, brewing a bad batch is a great opportunity for you to shock and entertain your beery friends with that most feared ritual of zymurgic horror, the Bad Beer Tasting.

Gruesome Fun

It’s not too difficult, and it’s actually kind of fun—if you’re in a gruesome mood (and have some clean ones to drink at the end). Invite brewers and interested non-brewers, and encourage those having bad beers to bring along a sample.

The format is a walk-around, with a number of specially prepared samples as well as problem beers. Some are meant to be tasted, such as beers that are purposefully damaged, or bland (light) beers with flavorings added. Others, because of their noxious nature, are meant for sniffing only. Recipes follow for both.

Label each flavor/aroma flaw sample and place it at an individual station. Provide small disposable cups to ensure that tasters sample only one defect at a time.

Participants go from station to station, noting the flavors and aromas associated with each defect. It is helpful to put out a sheet for notes, so people can share their observations with others. Such impressions can be helpful in recognizing and remembering flavors.

Another station holds defective beers, as yet undiagnosed. More experienced tasters should sample these and decide which category they should be placed into, either an existing category, or a new one (the following is not an exhaustive list), in which case a new label must be made. The rest of the group should taste these diagnosed beers, because the defects often taste different in situ than they do as artificially concocted samples.

Here’s a list of common beer defects—by no means complete—and a suggestion for how to prepare a sample for this tasting.

Diacetyl

This buttery aroma can be desirable in low concentrations in ales, but if it sticks out too far, it’s usually regarded as a defect. Produced by yeast, but especially by certain bacteria. To replicate: Add butter flavor extract (the kind used for baking), 1 to 4 drops or equivalent (1/2 teaspoon  dry to a light lager. Note that quality of diacetyl changes with quantity; for that reason, it might be useful to do a series at different dilutions.

DMS (dimethyl sulfide)

A vegetal aroma that can result from brew house procedure (wort held at high temperatures without boiling, usually) or, in extreme cases, from contamination. Actually regarded as a positive in some European lagers, where, in small quantities, it adds a certain richness. To replicate: Add juice from canned corn to light beer.

Skunkiness (methyl mercaptan)

The result of light hitting dissolved hop compounds, resulting in a rubbery, skunky aroma. To replicate: European beer in green bottle, placed in sunlight for an hour, then chilled and served normally.

Oxidized

A papery, wet cardboard flavor/aroma, the result of over-aged beer, enhanced by overexposure to air during the brewing process. Varies in quality from beer to beer. To replicate: Find the oldest, dustiest European beer in the liquor store. It should have haze or flakes on the bottom (don’t use weizen, because the haze is intentional). Go for beer in brown bottles only, as the ancient green-clad ones are often skunked as well as oxidized.