How Different Are We?
Not all animals share the repertoire of five basic tastes: cats, for example, can’t detect sugar, and this is a genetic mutation of great antiquity. So, a cat’s flavor world lacks sweetness, just as a dog’s visual world lacks full color. But, before we get smug about our own abilities, remember that our own sensory world is also incomplete compared with other animals: many species detect things we do not. Doubtless, these differences in perceptive abilities reflect the different evolutionary histories of different species.
Even among our close relatives in the primates, other species include things in their diets that we find unpalatable―presumably, these foods taste “good” to the animals that consume them.
Richard Wrangham, professor of anthropology at Harvard University, has studied dietary differences in the primates. In research on primates at the San Diego Zoo, he looked at animals’ responses to tannins, plant compounds that are both astringent and bitter.
“I found that the willingness to eat tannins, which are quite an important feature of alcoholic drinks in general, is strongly associated with how much leaf you eat in the wild,” says Wrangham. “Species that don’t eat any leaves in the wild completely reject tannins in captivity. Chimps and gorillas were tolerably tolerant.”
He also looked at responses to bitterness, using quinine. “There are so many different kinds of poisons that taste bitter. No one to my knowledge has understood the fundamental thing that makes something bitter.”
And yet, bitterness and astringency, tastes that are generally rejected, are sought out in beer and wine. Wrangham reasons “Basically, what happens is the receptors that taste bitter are able to attune themselves to things that―from that particular species’ point of view―would be bad.” Under the right circumstances, we learn to accept new flavors.
Looking only at humans, there are important differences in our ability to taste and smell. A baby is born with taste buds on the sides and roof of the mouth, which presumably is useful at a time when new flavor memories are being formed. Over time, the distribution and number of taste buds are reduced; older people are not as sensitive to flavor as youngsters.
Our capacities don’t just change through life, they also vary from one individual to another, and some of this variation is genetic. The best-documented example involves sensitivity to PTC (phenylthiocarbamide), a compound that ranges from unpalatably bitter to undetectable, depending on the subject’s genetic make-up.
Sensitivity to PTC has been used to identify so-called “super tasters,” yet there is little evidence that the ability to taste PTC generalizes to greater flavor sensitivity overall. In popular literature, “super tasters” are said to be more sensitive to bitterness and to alcohol in general―but the scientific evidence is yet to weigh in.
So, are hop-heads more likely to be “non-tasters,” unable to perceive the bitterness in PTC and similar compounds? Are “tasters”―those of us able to sense PTC―more likely to prefer malt-accented beer?
Susan Schiffman can’t establish a connection. She notes “In Japan, there are many more PTC tasters than in the American population, and yet Kirin beer is pretty bitter, right? In consumer tests, strong PTC tasting doesn’t seem to affect beer preferences.”
We also seem to differ in our sensitivity to some compounds that are relevant to brewing: diacetyl, dimethyl sulfide (DMS) and methyl mercaptan, in particular. Diacetyl, a product of fermentation, can be perceived at extremely low concentrations. At low levels, it is reminiscent of buttery theater popcorn, then butterscotchﾑbut not every drinker is equally sensitive. The same is true of DMS, which imparts cooked vegetable flavors, and methyl mercaptan, which contributes light sulphur notes appropriate to some beer styles, but which at higher levels smells to some drinkers like skunk.
Schiffman makes the good point that we don’t experience beer one taste or odor element at a time, but as part of an integrated whole that blends taste, feel and smell. Flavors that we dislike in isolation can be pleasant in the finished beer―when they occur in the appropriate amounts and combinations.
From Flavor to Sensory Analysis
Since the highest attribute of a beer is that it tastes good, as beer production scaled up to industrial levels, it makes sense that the emerging science of flavor analysis would be enlisted to make sure that beer was consistent and free of flaws.
Beginning in the 1960s until his death last year, the Danish chemist Morten Meilgaard defined the field of sensory analysis for the brewing industry. He saw this formal practice of analysis as one with a long history, closely linked to the rise of trade and the need of merchants for an objective assessment of the quality of the goods they were buying. For his part, Meilgaard’s goal was to codify beer flavor for the industry, establishing a common vocabulary of taste.
In his book Sensory Evaluation Techniques, Meilgaard explained that his approach was to “treat the panelists as measuring instruments.” He recognized that trained human tasters were far more sensitive than instruments in evaluating beer flavor, but that they were also prone to bias. But, he acknowledged “they are the only instruments that will measure what we want to measure, so we must minimize the variability and control the bias by making full use of the best existing techniques in psychology and psychophysics.”
Meilgaard’s Beer Flavor Wheel, adopted by the major professional brewers’ associations, is still a standard tool today. The wheel displays 97 attributes of beer, taste and aroma, both good and bad. Many attributes refer to familiar foods such as apple, coconut or cooked sweet corn. Others refer to familiar sensory experiences, though not foods: Bakelite, leather, or can-liner. Still others name specific chemical compounds or qualities that the educated analyst could trace to stages (or errors) in the brewing process: acetaldehyde, caprylic, or autolysed.