We have always known it. Some revere it, some only partially perceive it, others shrug it off. Whatever stance we take in the face of it, flavor runs a deep line through our lives, revealing ancient preferences, feeding our current ones, and performing, without us knowing it, a concert of molecular movement and electricity that triggers emotion, memory, pleasure or alarm.
Conventional Western thought once divided our tongue into regions of perception corresponding to four basic tastes: sweet, salty, sour and bitter. Added recently, umami (a borrowed Japanese word meaning “good flavor”) is considered the fifth taste. It refers to savory sensations, such as those created by meat or mushrooms. Sweetness, we were told, is perceived on the front of the tongue, bitterness at the back, salty, sour and umami at various locations along the sides.
This, of course, is over-simplification. Taste bud receptors of various kinds are located throughout the tongue, and in a range of concentrations. Our ability to taste is related to the number of papillae our tongue contains, and this concentration varies among ethnic populations.
Papillae are small bumps that house the taste buds and molecular receptors that attract certain flavor molecules in the food we eat. Bitter taste receptors attract bitter flavor molecules, transferring that information through tiny pore openings in the taste buds, where it is perceived by nerve endings and transferred to the brain.
Tongues, however, are blunt sensory instruments compared to those in our nasal passages. The old trick of holding your nose to swallow a distasteful bite works so well because it reduces our experience of flavor to the tongue alone.
When the nose becomes involved, flavor increases exponentially. Our olfactory sensors are themselves nerve endings. Unlike tongue receptors, which must pass flavor molecules through several channels of perception, olfactory nerves have a direct connection to the brain, giving them their heightened sensitivity. When working together, tongue and olfactory sensors are capable of detecting a delightfully wide range of flavor variation.
Olfactory signals go directly to the part of the brain involved with memory, especially that of place and experience. Tongue receptor signals travel to parts of the brain that, among other things, regulate our perception of fullness, control salivation, and, combined with the olfactory signals, create a conscious sense of taste, what we experience as the flavor of our food.
There are many reasons for our bodies to have a refined sense of taste. Flavor reliably indicates chemical attributes of the things we put in our mouths, and thus can function as an assessment of calories and nutrients. Sweetness indicates sugar and its associated vitamins and carbohydrates, salt provides an essential nutrient for organ function, sour indicates acidity that could assist the detection of rotten foods, while umami may reflect the presence of protein. Bitterness stands as our strongest indicator of danger—most poisonous alkaloids have a bitter taste, though this does not mean that all bitter foods contain harmful substances.
No taste exists in isolation. Greens such as mustards and radicchios do contain a strong bitter note, but one laced with sweetness. In the case of grapefruit, sweet and sour are also detectable. The presence of sweetness in particular can (but does not always) indicate that the type of bitter compound present is not dangerous. Such benign bitter compounds promote gastric juice production, thus aiding the digestion of accompanying vitamins, carbohydrates and fats.
Flavor is revelatory, and while it is a highly subjective enterprise (physiologically and otherwise), we are rewarded for paying it attention. We are not necessarily predisposed to try new things, to break the spell of habit and grab that unfamiliar bunch of greens to take home and sample. Yet, the more flavors we try, the more we learn about their nuances, and the more capable we become of discerning the many ways in which our foods feed us.
(Originally published in the Hillsdale Farmers’ Market newsletter, The Grapevine, January 31, 2013)