What Are the Five Basic Tastes?

Each basic taste is a chemical detection system with a purpose. Sweet signals sugars and available energy. Salty signals sodium, needed for nerve and muscle function. Sour signals acids, which can indicate unripe fruit or spoilage.

Bitter is the most protective. Many plant toxins are bitter, and humans have around twenty five different bitter receptors compared with roughly one type for sweet. That imbalance says a lot about which mistake evolution treated as more dangerous.

Umami was proposed by the Japanese chemist Kikunae Ikeda in 1908, who identified glutamate as the source of the savoury depth in kelp broth. Western science was slow to accept it, and the receptor was only confirmed in the early 2000s.

Umami detects amino acids, signalling protein. It is strongest in aged, fermented and slow cooked foods:

• •Parmesan and other aged cheeses
• •Soy sauce, miso and fish sauce
• •Ripe tomatoes, mushrooms and seaweed
• •Cured meat and long simmered stocks

This distinction matters. Taste is the five signals from the tongue. Flavour is the combination of taste with smell, texture, temperature and even sound, assembled by the brain into a single experience.

The proof is easy to run at home. Hold your nose and eat a jelly sweet and you will get sweetness and little else. Release your nose and the fruit flavour appears instantly. Much of what people call taste is actually smell, which is why food is uninteresting when you have a cold.

Almost everyone was taught a diagram showing sweet at the tip, bitter at the back and so on. It is a mistranslation of a German study from 1901 that was misread and then copied into textbooks for a century.

In reality all five tastes can be detected across the whole tongue. There are minor differences in sensitivity between regions, but nothing resembling the neat zones in the diagram. Taste receptors are also found in the throat and on the roof of the mouth.

Researchers are actively investigating additional candidates. The strongest case is for fat, where evidence suggests a specific receptor for fatty acids rather than fat being detected only by texture.

Other proposals include a taste for starch and one for calcium. The bar for adding a basic taste is high: it needs a distinct receptor, a distinct nerve pathway and a perception not reducible to the existing five. Fat is the closest to clearing it.

Taste sensitivity declines with age, partly through a reduction in taste receptor cells and more significantly through a decline in the sense of smell. This is one reason older people often report that food has become bland.

Illness and medication also matter. Many drugs alter taste directly, and respiratory infections block the smell pathway that carries most of what we call flavour. Zinc deficiency is a recognised and treatable cause of reduced taste, and sudden persistent loss of smell is worth mentioning to a doctor rather than dismissing.

Monosodium glutamate, or MSG, is simply the sodium salt of glutamate, the same substance that gives parmesan, tomatoes and kelp broth their umami depth. In 1968 a letter to a medical journal described symptoms such as numbness and palpitations after eating in Chinese restaurants, and the idea of a Chinese restaurant syndrome caused by MSG spread quickly. For decades many people avoided the seasoning, and some products still advertise the absence of added MSG on their labels.

Carefully controlled studies have struggled to support the scare. When people who believe they react to MSG are given it or a placebo without knowing which, consistent reactions at normal food amounts have generally not appeared, and food safety authorities regard it as safe for general use. Your body also cannot tell added glutamate from the glutamate naturally present in foods. Some researchers have noted that the original panic singled out one cuisine rather than the many foods rich in glutamate, which suggests that cultural assumptions shaped the story as much as the chemistry.

The five tastes are not all detected in the same way. Salty and sour work largely through ion channels, tiny pores in the membrane of a taste cell. Sodium ions from salt flow in through one kind of channel, and hydrogen ions from acids through another, changing the cell's electrical charge so that it signals to a nerve. Sweet, umami and bitter instead use receptor proteins that bind a molecule on the outside and trigger a chain of reactions inside. The sweet and umami receptors are built from related parts and even share one component, a sign of their common evolutionary origin.

Knowing the receptors explains some odd facts. Cats carry a broken version of one sweet receptor gene, which is why they show no interest in sugar, a loss that makes sense for strict meat eaters. Artificial sweeteners such as sucralose bind the same sweet receptor as sugar but activate it at tiny concentrations, which is why so little is needed. A protein from the West African miracle berry, called miraculin, binds the sweet receptor and switches it on when acid is present, so for a while afterwards lemons taste sweet. Taste cells are also replaced continually, which is why a scalded tongue soon recovers.

In 1931 a chemist named Arthur Fox was working with a compound called phenylthiocarbamide, or PTC, when some of the powder blew into the air. A colleague complained that it tasted intensely bitter, but Fox, who had also been exposed, tasted nothing at all. Testing friends and family showed that people fell into two broad groups, tasters and non-tasters, and that the trait ran in families. It became one of the classic examples used to teach human genetics, decades before anyone knew which gene was involved.

In 2003 researchers identified the main gene responsible, TAS2R38, which codes for one of the bitter receptors. Common versions of the gene make the receptor either sensitive or almost blind to PTC and similar molecules, and roughly a quarter of people of European descent are non-tasters, with proportions varying between populations. Later work described a further group, sometimes called supertasters, who find related compounds intensely bitter. Similar chemical groups occur naturally in vegetables such as broccoli and Brussels sprouts, which may explain part of why opinions about them differ so sharply.

The five basic tastes are sweet, sour, salty, bitter and umami, each detecting something biologically important, and since most of what we call flavour comes from smell, taste alone is only a small part of the eating experience.