Like most people, I firmly knew in my childhood that there are four tastes: sweet, salty, sour and bitter. I first learned this in my native language, Russian, then in German, and finally in English. I was quite comfortable with this concept until I became interested in taste science. Then, it appeared to me that some foods have a taste quality that could not be described by any of these four sensations. What was this other taste sensation? It turns out that I was not the first person who wondered about this. Over a century ago, a Japanese chemist, Kikunae Ikeda, was trying to explain “the peculiar taste” arising, for example, from fish or meat, which he believed was distinct from the four known tastes. He called this fifth taste “umami” (loosely: deliciousness/savory) and found that it is evoked by glutamic acid and its salts.
What is Umami?
Because I am a neuroscientist writing for flavorists, let me start with terminological conventions, which sometimes differ between these two fields.
Flavor and taste: For a neuroscientist, flavor is a complex sensation arising from stimulation of several distinct sensory systems: gustatory, olfactory and somatosensory (touch, temperature, pain, etc.). Each system has its unique anatomical and functional organization. The gustatory system in mammals includes taste receptor cells that are organized in taste buds. Most of the taste buds are located within gustatory papillae on the tongue, but some buds are present in other parts of the oral cavity, for example on the soft palate. Taste stimuli interact with the taste receptor cells, and this activates gustatory nerves and subsequently brain structures involved in gustation. Some brain structures that receive sensory information from taste receptor cells also receive input from olfactory and/ or somatosensory systems. Integration of the input from these three distinct sensory systems results in the complex perception of flavor. We consider umami a taste sensation because known umami taste stimuli activate all levels of the gustatory system.