THE FUTURE OF FOOD The Science of Yummy

Compared with the puzzle of smell, taste is much more straightforward. "Taste evolved as a sense to make very important decisions about nutrients," explains Gary Beauchamp, director of the Monell Chemical Senses Center, a nonprofit research center in Philadelphia specializing in taste, smell and chemical irritation. Sweetness signals the presence of calories, vitamins and minerals. Saltiness indicates the presence of sodium (important to keep your heart and neurons going). Bitterness screams "this could be poison!" at your brain.

You detect tastes, of course, with clusters of cells on your tongue-taste buds. And on those cells reside the receptors; most data indicate that there is one type of receptor per cell. Sweet, bitter and umami tastes are basically lock and key. A taste molecule of a certain shape (the key) will bind with a receptor that's the complementary shape (the lock). And even though research reveals multiple subtypes of the bitter receptor-12, or 20, or up to 50, depending on who you ask-as far as we can tell, when they are activated, it is perceived without nuance. Of all the receptors on the tongue, we know least about how salt and sour interact with their respective target taste molecules.

A third component of flavor is chemesthesis-the feeling of heat, coldness, pain or tingling. Sensate research, as it's known, began in the 1950s but really didn't take off commercially until the 1990s, and a slew of sensate products have hit the shelves since. "Cool Burst" and "Ice" show up on the label of products containing a non-minty cooling molecule, which acts directly on cold receptors in the skin of the tongue. Warming sensates, like the molecule camphor, trigger warm receptors, also found in the skin. A compound isolated from the Szechuan pepper will make your tongue tingle. And then there's capsaicin, a compound found in hot chilies, which acts on both warm receptors and pain receptors in the mouth. Sensates have an advantage over other flavorants: A person can acclimate rapidly to certain smells and tastes because those neurons tire out quickly, but the sensate-receptor neurons' pathways continue to fire for a longer period of time. For example, the tingling sensation from the Szechuan pepper can last for 20 minutes.

Recent research has centered on the search for sodium, sugar and MSG enhancers that make food taste good with minimal added sweeteners or salt. "It's a numbers game," says Mark Zoller, executive vice president of discovery and development at Senomyx, a company in San Diego that finds receptor-linked taste compounds by screening several hundred thousand molecules out of its library of 500,000 synthetic and natural compounds every year "to find that needle in the haystack." The company's umami enhancer, capable of replacing or reducing MSG, is already in products by Nestl. And in August, Senomyx announced that it is developing an enhancer to increase the perceived sweetness of sucralose that may allow food manufacturers to use up to 75 percent less of the sweetener in processed foods without any loss of the desired sugary hit.

But understanding the physical processes on the front end of flavor perception is like understanding only the plumbing. Signals from the tongue and nose must still be interpreted by the brain, in areas like the orbitofrontal cortex (which is associated with reward, decision-making and flavor recognition), the hypothalamus and amygdala (involved in the emotional component of smell), and the hippocampus (associated with memories, including food cravings). That's the stage where things like memories and unconscious judgment come in.