Umami is a distinct, difficult to describe flavor caused by the interaction of glutamates, a naturally occurring amino acid, with receptors on the tongue. Some people call it “the fifth taste,” as it is distinctly not sweet, sour, bitter, or salty, but is instead sometimes called savory. In addition to having a unique standalone flavor, umami appears to enhance foods it is combined with, making other flavors richer and more intense. The concept is ancient, although the official term is relatively recent.
Every time someone puts ketchup on fries, they are using the principle of umami. Both potatoes and tomatoes have high amounts of free glutamates, which interact with each other to create a distinctive flavor. Other foods with an abundance of free glutamates include seafood, shiitake mushrooms, meats, carrots, and seaweed, among many others. Many of these foods have been traditionally paired to enhance their natural flavor.
The discovery of umami is credited to Kikunae Ikeda, a researcher at Tokyo Imperial University. Ikeda was researching the unique flavor of seaweed broth when he isolated a distinctive compound that he identified as savory, since it did not fit with the other four identified tastes. Ultimately, he managed to separate a unique white powder with a crystalline structure, which came to be known as monosodium glutamate, or MSG. Ikeda's discovery paved the way to many developments in food science and to a restructuring in the way people though about taste.
In addition to modern day examples, the flavor has also been harnessed historically. It appears in high concentration in cured and fermented foods, such as the Roman garum and an assortment of traditionally fermented Asian sauces such as soy sauce and fish sauce. This flavor has classically been used as a condiment, to enhance the flavor in other foods, bringing out their natural savory taste.
There has been some controversy over this flavor. Some people believe that it is not, in fact, a distinct flavor, and wish that it was not classified as the fifth taste. Others have historically had concerns about glutamates, and MSG in particular, claiming that the compounds have deleterious health effects. Especially in the West, the concept was not as readily adopted as it was in Asia, as is reflected by the lack of an English word for the taste. Western chefs have slowly embraced the concept, however, designing dishes which harness the power of umami, whether it is truly a distinct taste or simply a subset of another.