In most families, it wouldn’t be the holidays without food.

Of course, we need food for nourishment, but what is it about food that makes it so pleasurable?

Taste is one of our five senses – along with touch, sight, hearing. But science has only recently begun to understand just how complex our tasting mechanism is.

Cuisines, of course, vary worldwide, dependent on native spices, plants, animals and cooking traditions. Perhaps as a result, different cultures start with different understandings of taste. In the traditions of Western Europe, the U.S. and Canada, only four basic tastes are recognized: sweet, sour, bitter and salty. Alongside these four, Japanese eaters always recognize a fifth: savory. In South Asia, the four are augmented with two others, pungent and astringent.

In recent years, in efforts to reconcile these differences and understand how the taste mechanism might affect human health, scientists have conducted significant investigations of how we perceive the flavor of food. They have discovered that flavor is somewhat different than taste and have identified a number of tastes beyond the common four. They are beginning to see connections between taste and health, opening the possibility that health can be improved through better understanding of why individuals chose the diets that they do.

Flavor

Flavor is perceived in a number of ways. Most basic, perhaps, is the gustatory system through which taste buds perceive tastes and transmit them via nerves to the brain. Taste buds are clumps of taste receptors. Through chemical and electrical reactions, different kinds of receptors react to different foods with messages to the brain. The mouth has thousands of taste buds, mostly on the tongue but also on the roof and the back of the throat.

In addition to taste, however, flavor is influenced by smell and texture. The mouth contains receptors that detect these sensations and alert the brain using pathways different than the taste buds.

While the system for registering flavor is generally the same in all people, slight variations make individuals more or less sensitive to various flavors.

New Tastes

Umami. Although always considered a basic taste in Japanese cuisine, savory – or umami, as it is known in the scientific community – was not among the basic tastes first catalogued by western scientists. In 1908, a Japanese chemist proposed that umami be added the list. It was officially recognized at a global conference on taste science in 1985. In addition to savory, words used to describe umami include “meaty” and “brothy.” The taste derives from the detection of glutamate, a by-product of certain amino acids that is common to meats, fish, shellfish, spinach, aged cheese, Chinese cabbage, ripe tomatoes and other vegetables. It is also present in ribonucleotides (notably, in shitake and other mushrooms, some seaweeds and Chinese leeks). In combination, glutamates and ribonucleotides amplify the umami taste. As a result, most cuisines include dishes that combine these two (for instance, Italian: parmesan cheese, tomato sauce and mushrooms; Scottish: cock-a-leekie – chicken stock and leek – soup). The umami taste is also present and first tasted in breast milk.

Fat. A scientific consensus is emerging that fat should be considered a basic taste. The presence of fat is perceived through the trigeminal nerve which registers the touching experience of something slippery, creamy or viscous in the mouth. This fact leads some scientists to say fat is felt rather than tasted. By whatever specific means, however, fat is perceived distinctly by receptors in the mouth, and the health implications may be significant. Small-scale studies show that some individuals more readily identify solutions that contain tiny amounts of fatty oil. This suggests that some people may be more sensitive to the taste of fat and may have genetic conditions that heighten fat cravings.

Calcium. Because calcium is critical to bone growth, muscle contraction and cellular communication, it seems reasonable that humans evolved to detect its presence in food. New research shows that mice have two taste receptors for calcium, and follow-up investigation indicates that humans have at least one. How it works and to what impact remains for further discovery. Calcium’s taste can be described as “chalky,” and some scientists speculate that its unpleasant taste is designed to ensure that humans do not eat too much of it. In milk, however, calcium’s taste is masked by the way it binds with fat. Generally, Americans do not consume enough calcium (four out of five are deficient), in part because they do not eat enough vegetables. Scientists speculate that this may be because they are overly taste-sensitive to calcium.

Piquance. Hot peppers and other spicy foods are highly prized in many cuisines, but whether their burning sensation is a taste or not remains a topic of scientific debate. These foods trigger a response in receptors that tell the brain how hot the food in the mouth is (too hot – above 107.6 degrees Fahrenheit – and it must be spit out to prevent burns). Piquant compounds found in hot peppers act on this receptor to lower its activation temperature. So, while a pepper in the mouth is actually no hotter than, say, the tomatoes in its salsa, the receptor tells the brain that this food is “HOT!”

Coolness. Other foods have the opposite effect of piquance. They trick a different sensor into telling the brain something is cooler when, in fact, it is the same as other food in the same bite. Peppermint and menthol, for instance, activate this sensor.

Metallicity. Although lab tests have yet to identify a specific metal taste receptor, scientists speculate that one exists. Some metals, in combination with saliva, act like a tiny battery, producing millivolts of electrical energy that are transmitted to the brain as a metallic taste.

Kokumi. The same Japanese food company, Ajinomoto, that helped convince the world that umami is a basic taste is currently promoting another new candidate: Kokumi, meaning “mouthfulness” or “heartiness.” According to a 2010 research paper, certain food compounds interact with the mouth’s calcium receptors (differently than calcium) to produce an enrichment of whatever flavors are already in the mouth. Braised, aged or slow-cooked foods contain these compounds.

Carbon Dioxide. A last new taste candidate is carbon dioxide, the gas that gives soda, beer and champagne their fizz. The tingling it provides is caused by the physical sensation (touch) of bubbles bursting on the tongue, but recent research indicates that (at least in mice) a taste bud sensor detects carbon dioxide and informs the brain of its presence.

In general, the basic science of tastes is still taking shape. We may learn much more about how our bodies perceive and react to food in the years to come.

In the meantime, the family gatherings and feasts of the holidays provide ample opportunity for personal taste exploration. Grazing on old favorites and new treats, see how many tastes you can detect.

Happy Holidays from the LHSFNA!

[Steve Clark]