The five tastes usually given are: Bitterness, Sourness, Sweetness, Saltiness, and Umami. In the west, the umami taste has only recently been included, and a number of other possible tastes, notably one for fattiness and one for metallic or calcium tastes, have also been proposed.
The five tastes are conveyed to the body through receptors found throughout the mouth, called taste buds or gustatory calyculi. The vast majority of taste buds are found on the top of the tongue, but some are also on the roof of the mouth. In addition, the sense of smell plays a large role in conveying taste to people, and people with impaired or non-existent senses of smell may find it difficult to impossible to taste any of the five tastes.
The idea of having a few primary taste senses in the Western world goes back to Aristotle. He separated taste into two main areas: bitter and sweet, and then further subdivided these into the tastes of: puckery, sour, salty, succulent, harsh, and pungent. In the East the Chinese integrated the idea of fundamental tastes into their idea of the five elements, giving five tastes as well: sour, sweet, salty, spicy, and bitter.
There is a common misunderstanding that holds different parts of the tongue are responsible for the perception of the five tastes individually. Even medical texts would present the physiology of the human tongue this way. It is thought that this was the result of a mistranslated German text, and somehow became propagated throughout the West. In fact, each taste bud has hundreds of individual receptors, and each taste bud is capable to recognizing any of the five tastes. While there are some very slight differences in terms of sensitivity on different parts of the tongue, these are incredibly small.
For a long time in the West, the four tastes given were simply bitterness, sourness, sweetness, and saltiness. It was thought that these four tastes covered every taste available. Recently, however, the taste umami, which has long been included in Eastern ideas of primary tastes, has been added to the discussion in the West.
Sourness is a taste that can be found in foods such as lemons, vinegar, and certain under-ripe fruits. Sourness is conveyed through ion channels, which look for hydronium ions, which are formed by water and acids. Sweetness is a taste that can be found in many ripe fruits, and sugar. Sweetness is conveyed by a number of taste receptors that couple to the G protein gustducin.
Bitterness is a taste that can be found in foods such as beer, grapefruit, and raw chocolate. The most bitter substance known is a synthetic chemical, known as denatonium, which is used as an additive in toxic chemicals to help cue people who accidentally ingest it. Bitterness is conveyed through certain taste receptors which couple to the G protein gustducin. Saltiness is a taste that is provoked by the presence of salt ions in foods. Like sourness, it is detected by ion channels, that look for salt compounds.
Umami, the fifth of the five tastes, is a taste provoked by the presence of glutamate. Umami is provoked mostly by fermented foods. In classical expressions of the tastes, the umami sensation was often described as savoriness, or meatiness. The umami taste most people are familiar with is that provoked by the presence of monosodium glutamate, or MSG.