Scientists have discovered a sixth taste, although they can’t actually agree on what it tastes like.

Researchers in the United States say the sixth taste is calcium, a sort-of bitter, sort-of sour flavour that they have identified as having its own taste receptors in the tongue.

Researchers in Japan call it kokumi and say it doesn’t actually have a taste in itself: It enhances taste by triggering calcium receptors in the tongue.

Both teams agree on calcium. They disagree on how and why it works.

The upshot is the Western mouth is turning out to be more sophisticated than science realized. Which is good news for the future of nutrition.

Kokumi translates roughly as heartiness. It explains, for example, why meat that’s slow-roasted for 12 hours tastes better than meat cooked for one, or why aged Gouda tastes better than the new stuff.

Like umami, the similarly Japanese discovery of a special savouriness in food such as soy sauce, kokumi’s vague definition baffles even the best-trained testers.

“I don’t know what kokumi is,” says Michael Tordoff, a research scientist at the Monell Center in Philadelphia and discoverer of calcium receptors. “I’ve talked to the scientists. They brought me samples. We do not know what these Japanese scientists are talking about.”

Tordoff remains a curious scientist, though. “It might be we’re just not well-educated. It would be nice of it was based on calcium.”

Ajinomoto, a Japanese seasonings and food product company, discovered kokumi and is already marketing it in one form: yeast extract. Among other things, it can replace the discredited MSG (monosodium glutamate) as a food enhancer.

Their findings were published in the November 2009, and January 2010, editions of The Journal of Biological Chemistry.

Ajinomoto also brought some of the world’s leading chefs to Hong Kong in October for a kokumi cook-off. Among them were Jordi Roca of El Celler de Can Roca in Girona, Spain; Alvin Leung of Bo Innovation in Wan Chai, Hong Kong; and Paul Virant of Vie in Chicago.

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Celebrity chefs aside, Tordoff will continue with his research to understand if calcium taste receptors exist in the brain as well as the tongue.

“A lot of my colleagues are stuck in the four-taste model,” says Tordoff. “I already believe there are more tastes. There is evidence for a taste for fat, or for other mineral tastes, for iron and copper. Here we are in the 21st century and we don’t know a lot about how we taste yet.”