The Hungry Lizard Inside Your head
Let’s start with your sensory system. Smell and taste serve to give us information about good and bad things in the environment. As animals evolved, plants co-evolved their ability to create flavors and aromas as a way of getting us to do their bidding. Sweet, fruity flavors are a sign of nutritive value, a trick plants use to get animals to distribute their seeds. Bitterness is a repellant or poison that lets us know the plant doesn’t want us eating it. Our organoleptic system deals with many other aspects of the environment. It’s no surprise that one of the musty markers for stagnant water is the most potent aroma chemical known, with a threshold in the parts per quintillion.
Taste and smell are separate sensory systems, but are sometimes hard to tease apart. Taste is the simpler of the two.
As every schoolchild knows, our tongues are covered with small bumps called taste buds. And while the familiar “taste map” delineates different regions for sweet, sour, salty, etc., modern science has shown this to be a fallacy derived from a bit of 19th-century pseudoscience akin to physiognomy, in which personality traits were supposed to be mapped by the bumpy irregularities on the noggin. Despite its untruth, the tongue map has been firmly wedged in the textbooks ever since. In reality, all areas of the tongue are sensitive to all taste sensations.
Look at your tongue in a mirror and you will notice that among the field of small bumps are a number of larger ones. These are the buds responsible for bitterness. The useful bit of knowledge is that because they are larger, it takes longer for the sensation of bitterness to fire the neurons that send the signals to the brain, and once stimulated, longer for the sensation to go away. Tasting, as you probably already know is not a single moment’s experience, but a process that takes a while to develop, build, and then fade to an aftertaste. Pulling apart this time dimension is an important goal of sensory training, and it is helpful to understand details like the longer time-constant of bitterness.
It used to be thought that there were only four tastes: sweet, sour, salty and bitter. Now it appears as if there are two more. The fifth is umami, or the glutamate receptor, important in fish and seaweed-accented Asian cuisine, but unimportant in beer. The sixth is fat, which scientists have recently decided is an actual flavor and not just a mouthfeel sensation. Sweetness and bitterness are obviously big players in beer flavor, and, although it might not taste so, beer is actually fairly acidic. Saltiness comes into play only with certain water types, where is typically adds a sense of palatefulness.
There are other sensations in your mouth beyond taste, called trigeminal sensations after the big nerve that serves many functions in the facial area. Heat and cold are perceived, of course, but tickling, tingling sensations of carbonation, perceptions of heaviness or oiliness, astringency, and chili heat also come through these pathways. All of these sensations may offer clues to the nature and quality of a beer.