Taste – or gustation – is the one of the traditional five senses along with sight, hearing, touch, and smell. Taste usually refers to the ability to detect flavor, although smell, texture, temperature, and sight are also contributing factors. Humans experience taste through sensory organs called taste buds (or gustatory calyculi), located on the upper surface of the tongue on raised protrusions called papillae. Fungiform papillae are mushroom-shaped, and found on the tip and sides of the tongue; circumvallate papillae are the ten to fourteen dome-shaped dots at the back of the tongue; and foliate papillae appear on the sides of circumvallate papillae and the sides of the base of the tongue. Paintbrush-like filiform papillae are most common, but sense texture and touch rather than taste. Although the widely taught taste map implies taste is localized to certain parts of the tongue, taste-perception is evenly distrusted and all tasting papillae can sense every basic taste.
Saliva dissolves substances in the mouth, bringing molecules and particles to receptors responsible for each basic taste. Three tastes of the five basics tastes are perceived through specialized G protein-coupled receptors – receptors that sit on the papillae surface and activate complex changes within the cell. Sweet is mainly triggered by sugars, although non-sugar substances like aspartame also do the trick. Bitter comes from plant-based foods such as coffee, beer, olives, and citrus peel. Bitter is the most sensitive of the five tastes, and perhaps the most evolutionary vital: most poisons have a bitter flavor. Finally, umami – often translated as “meaty” or “savory” – is due to glutamate from meat, cheeses, beans, some vegetables, and – most famously – MSG. Although umami was first described in Asia in 1908, it was only recently adopted as a basic taste in the West.
The two remaining tastes are produced by ion channels that capture charged particles. Salty is produced by cations like K+ (potassium) and Li+ (lithium), although Na+ (sodium) taste saltiest. Similarly, sour reflects a drop in the mouth’s pH, triggered by the presence of hydronium ions (H30+) formed from acids and water.
Although the basics tastes and the way they’re perceived are constant across humanity, there is some variation. For example, while both males and females are better able to distinguish tastes as they age, women – on average – have more refined palettes then men. An estimated 25% of people are supertasters, who – partly due to more fungiform papillae – have a heightened sense of taste. These individuals are most often women, and tend to shy away from the more extreme flavors of coffee, beer, grapefruit, and bitter vegetables. Likewise, the world’s similarly sized nontaster population endures reduced numbers of papillae and a subsequently diminished sense of flavor. With so much biology influencing what flavors we can and cannot stomach, it seems that taste isn’t simply a matter of taste after all.