How many tastes are there?

How many basic tastes are there? Most people list four: sweet, sour, salty and bitter. Those with a background in the chemosensory sciences usually add a fifth, umami. But why stop there? There is growing evidence that there are more—perhaps many more. The idea that there are four basic tastes goes back at least as far as ancient Greece, so if there are more than four basic tastes why haven't they been discovered by now? There are three reasons: The first is that research on taste has been self-fulfilling. Scientists who believe there are four basic tastes conduct research on the four basic tastes! This richens the literature on the four basic tastes, and thus strengthens the impression that there are only four tastes worthy of study. It's very difficult to work (and fund) outside the box. The second reason is that there is a natural reluctance to open this box—a Pandora's Box— if things can be explained satisfactorily with the basic four (or five) tastes. Occam's razor argues that the best explanation is the one with the fewest components, and until recently, four (or five) basic tastes have seemed to do the trick. The third reason why we have been limited to four basic tastes is that, until recently, there haven't been the tools available to identify others. However, over the last decade or so, there has been a revolution in the study of taste, which has been spearheaded by the invention of new molecular and genetic tools that allow investigation of cellular and intracellular events. These have, for the first time, revealed the identity and nature of taste receptors. They allow us to determine that a particular taste receptor exists, find where it is located, and establish what it can and cannot detect. Monell has been at the forefront of this research, being among the first to discover the sweet taste receptor (2), paving the way for the discovery of some bitter taste receptors (1,8), and having a large industry-sponsored program to discover the salt taste receptor(s). To mix modalities and metaphors, taste science has been in the dark—or dark ages—and we are now beginning to see a new and much bigger picture. We are beginning a renaissance, with new findings leading to new ideas. My contribution to this picture has been the discovery of taste receptors for calcium. It has been known since the 1930s that rats …