Umami was discovered by a Japanese researcher one hundred years ago. Dr. Kikunae Ikeda of Tokyo Imperial University recognized that certain foods like asparagus, tomatoes, meat and cheese all shared a common taste. It's a bit hard to put your finger on, though it's often described as "savory." I think it's easier to think of it as the taste that makes your mouth water. It also has a distinctive mouth feel, it lends a fullness or roundness.
One of the first things I learned at a recent Umami Symposium is that while taste and flavor are often used interchangeably, they are not the same thing. Flavor is determined by taste and smell. There are only five tastes--sweet, salty, sour, bitter and umami. Just as sweetness is imparted by sugar, umami is imparted by glutamate, a type of amino acid, and ribonucleotides, including inosinate and guanylate, which occur naturally in many foods. It is also manufactured in monosodium glutamate. It is added or occurs naturally in products with hydrolyzed soy protein and autolyzed yeast such as Marmite, Vegemite, Maggi, and Kewpie mayonnaise. It also exists in most cheese flavored snack foods.
I'm not going to talk about the myths surrounding MSG in particular "Chinese Restaurant Syndrome," but I will say that I particularly like cooking with the naturally occurring sources of umami. Parmesan cheese, Worcestershire sauce, dashi broth, fish sauce, bouillon, tomatoes, shiitake mushrooms and even potatoes are all sources of umami. Mixing and matching is fine. I sometimes add Asian fish sauce to chili and while not perceptible, I find it helps to round out the flavor.
Scientists and chefs alike are interested in umami. While the isolated glutamate does not taste very good on it's own, research shows that it enhances the taste of many foods which is why umami was considered a "flavor enhancer" for so long before being recognized as a taste. It makes food taste better and can be used in making healthy foods more palatable for people who have a decrease in their ability to taste due to health or age.
One of the symposium panelists, author and scientist Harold McGee mentioned that the chef Heston Blumenthal found the flavor of umami to be stronger in the seeds and surrounding juice of tomatoes than in the pulp. Coincidentally, he pointed out that Ferran Adria had created a dish using the seeds and surrounding liquid instead of the tomato flesh or pulp. The dish served at El Bulli was Blood Orange Foam with Tomato Seeds and Sorbet. Even if you aren't thinking about umami, you might be using it to make dishes taste good. In case you missed it, check out the amazing lunch served at the symposium, prepared by chef Kunio Tokuoka, chef Hiro Sone and chef Thomas Keller.
If you'd like to learn more about umami, register with the Umami Information Center. You'll receive both newsletters and a free copy of a book called "Umami The World" which overs both the science and culinary aspects from both a Western and Eastern perspective.