Kokumi: The sixth-ish taste that adds richness and depth to savory foods

Kokumi is another word that just about everyone has experienced and understands, however without an actual "word", the topic is an internal one for most and thus goes undiscussed; hanging out in the background, there as a concept but not readily available for discourse. Kokumi can be described as the silkiness that coats your mouth and amplifies the taste of slow roasted meats, or the richness of depth in a consommé. Ajinomoto Group were the first to isolate the kokumi enhancing peptide glutathione in 1990, and describes kokumi as:

It's well established that there are five basic tastes: salty, sweet, sour, bitter, and umami. But there seems to be more to how we perceive taste than this simple fact would suggest. For example, when a soup or a stew has simmered for several hours, it takes on a richer, deeper flavor. And when cheese is allowed to mature, its flavor becomes more complex and lasting. What accounts for this form of enhanced deliciousness?
For over a century following Dr. Kikunae Ikeda's identification of umami, the Ajinomoto Group has been researching tastes and how we perceive them. In the 1980s, we began investigating what onions and garlic bring to so many flavorful dishes, something quite different from umami. Many have described the sensation as kokumi. Kokumi is a Japanese word literally meaning "rich taste". While umami imparts savory flavor or meatiness, kokumi* is a sense of richness, body and complexity that some compare to the way wines age and improve over time. Although kokumi substances have no taste of their own, they seem to make other foods taste and feel better, enhancing not only umami but also salty and sweet flavors.

Kokumi substances | Ajinomoto Group

Ajinomoto Group classifies kokumi as a flavor modifier, not a sixth taste so perhaps kokumi is more like those BASF commercials from yester-year with a tagline that goes: "we don't make a lot of the products you buy, we make a lot of the products you buy, better."