Humans taste sensory organs, called taste buds, appear to be receptive to relatively few chemical species as tastes. This contrasts markedly with the sense of smell, where very large numbers of different species can be differentiated.
There were originally thought to be four basic tastes, which are:
- Saltiness, produced by the presence of sodium chloride (and to a lesser degree other salts).
- Sweetness, produced by the presence of sugars.
- Sourness, produced by acids.
- Bitterness, produced by alkaloids and other chemicals.
In recent years a fifth taste, often described by the Japanese word Umami, has become widely although not universally accepted. It is produced by the free glutamates commonly found in fermented and aged foods, and in the additive MSG (monosodium glutamate).
For many years, books on the physiology of human taste contained diagrams of the tongue showing levels of sensitivity to different tastes in different regions. There is no scientific foundation for these "maps", which were based on a misinterpretation of old research.