It all comes down to our taste buds. It has long been known that there are four basic tastes - sweet, sour, salty, and bitter. It is now thought that there is a fifth taste, called "umami." Umami is the savory taste that occurs naturally in foods such as tomatoes and ripe cheese. Just as eating chocolate stimulates the sweet taste receptors on our tongue, eating food seasoned with MSG stimulates the glutamate or "umami" receptors on our tongue, enhancing the savory flavor of these foods.