Traveling to far-flung parts of the world and trying out dishes that offer new tastes and sensations presents a great opportunity to explore umami. It's easier to find it in something you've never had before than in, say, a hamburger.
The word umami comes from the Japanese umai, which means “delicious;" it's the fifth basic taste that can be sensed by specialized receptor cells on your tongue (after salty, sweet, sour, and bitter). Unlike the other four tastes, though, umami can’t be defined in a single word. This fifth taste is one of deep and full flavor, often described as meaty, rich, savory, or brothy.
It wasn’t until modern times that umami was identified as a taste. At the beginning of the twentieth century, Professor Kikunae Ikeda of Tokyo Imperial University noted: “There is a taste which is common to asparagus, tomatoes, cheese and meat, but which is not one of the four well-known tastes of sweet, sour, bitter and salty.” In 1907, he began experiments to identify the source of this distinctive taste. He knew that it was present in the “broth” made from kombu (a type of seaweed) found in traditional Japanese cuisine. Starting with a tremendous quantity of kombu broth, he succeeded in extracting crystals of glutamic acid, an amino acid and a building block of protein. 100 grams of dried kombu contain about 1 gram of glutamate, the sodium salt of glutamic acid. Professor Ikeda found that glutamate had a distinctive taste, different from sweet, sour, bitter and salty. He named this taste “umami.”
A umami food contains high levels of glutamate, which is present in plant and animal tissues. According to culinary scientists, the more umami present in the food, the more flavorful it will be. When you combine umami-rich ingredients in a recipe, you create layers of nuanced flavor.
Among the foods containing glutamate−and, thus, umami−are beef, duck, chicken, tomatoes, mushrooms, seaweed, green tea, oysters, milk, beets, soy sauce, and aged cheese. As far as cocktails go, a Bloody Mary is about as umami as it gets. If you’re going alcohol-free, try a glass of V8 or tomato juice.
The Mushroom Council has created a downloadable .PDF, Umami: Discover the Taste of Nature’s Hidden Treasure, that explains the basics and offers recipes. It's a bit mushroom-oriented, but provide a lot of great info.