Researchers hone in on the elusive receptor for sour taste

Sour is the taste of summer, a taste that evokes lemonade stands and vine-ripe tomatoes. Among the five basic tastes -- the others being bitter, sweet, salty and umami -- it is arguably the most subtle. In small amounts, it adds a critical tang to an otherwise bland dish. At higher concentrations and on its own, it's unpleasant or even painful.