Taste is the sensing of flavor in food and other material that is ingested. Taste is possible because chemicals stimulate receptors on the tongue, the taste buds. How something tastes can tell an individual whether that something is food or inedible, like cardboard, and toxic substances often have a disdainful taste, something that some animals and insects use to their advantage.
The four common types of taste often taught to schoolchildren are the basic sweet, salty, bitter, and sour sensations. However, a fifth taste was recently added to the list, savory (also known as meaty or umami).
The bumpy texture of the tongue, which is often visible, is caused by the taste buds (sometimes called gustatory cells). The bumps are actually called papillae, and within them are microvilli, microscopic hairs that send messages to the nervous system. These nerve endings are stimulated by chemicals. The average person has thousands (approximately 10,000) of these taste receptors on their tongue, and the taste that is tasted depends entirely on which chemical signal is sent.
Saltiness is perceived when ions, including sodium, magnesium, potassium, and often calcium, are present in the saliva or on the tongue. The receptors respond more strongly to sodium, making it seem saltier.
Sour is perceived when acidic compounds activate hydrogen ion channels, which depolarizes the gustatory cells. This allows the two tastes to be different, though the signals are relayed in a similar manner.
Sweetness is a response to sugars and other molecules, including aldehydes, ketones, and the amino acids glycine, alanine, and serine.
Bitter has been found to have a genetic component; some people taste certain foods as bitter, broccoli for example, while others do not. This may explain why it was the last of the four to be added to the common list, by the Greek philosopher Democritus. Most naturally bitter compounds are toxic, which may indicate an evolutionary component to the taste. However, some medicines, such as the anti malarial quinine, and common foods, such as coffee, beer, unsweetened chocolate, and citrus peel, are also bitter.
The most recent taste is thanks to a French chef named Escoffier, who became famous in the 1800s for creating dishes that tasted like none of the four taste sensations. This new taste came from his use of veal stock. Asian cooking uses this same flavoring as a fundamental taste in their dishes. A Japanese chemist, Kikunae Ikeda, published his findings about the key chemical in the journal of the Chemical Society of Tokyo. The chemical was glutamic acid.
Glutamic acid, or its basic form glutamate, is often found in fermented or aged foods. The taste is now known as meaty or savory, but the name given by Ikeda 100 years ago was umami. Umami is Japanese for “yummy” or “delicious”. In 2002, scientists found that there is indeed a fifth tastebud, one that senses L-glutamate.
So there are currently five known basic tastes sensed by the taste buds on the human tongue: salty, sour, sweet, bitter, and umami.