Mouth as a dishwasher
Photo: Adam Voorhes
She peeked into human cadavers for Stiff, then tackled the science of sex in Bonk. Now, in Gulp, writer Mary Roach ventures inside our bodies to find out what goes on as—and after—we eat. Sound icky? Not to Roach, whose research took her from Northern California (where she learned how to taste-test olive oil) to the Netherlands (where she visited a lab that studies how we chew). "The poor alimentary canal gets no respect," Roach says, "but it does some pretty fascinating stuff." A few of her favorite findings:

Your nose has more to do with eating than you might think.
"You could actually throw away your tongue and still 'taste' a lot of what you eat, because smell accounts for as much as 80 to 90 percent of how we perceive food. In fact, we have two sets of nostrils—the ones we see and a second, internal, set at the opening in the back of the mouth that leads up to the nasal passage. As you chew, some of the airborne molecules that are wafting around in your mouth go through this internal nose, and your brain processes the odors of what you're consuming. If you want to experience more complex, fabulous flavors, take a tip from wine connoisseurs: Hold the food in your mouth for a few extra seconds and breathe out through your nose so that all the aromas have to travel through your inner nostrils."

Your ears play a big role, too.
"You can change how appealing a food is by simply manipulating the sound it makes when you chew. This is particularly true with crunchy and crispy foods. In one study, researchers put headphones on a group of people and altered the pitch and loudness of the crunch they heard as they bit down on potato chips. If the crunch was muted, the testers judged the same chips to be staler than they were. There's likely an evolutionary reason for this: As a species, we probably acquired a dislike for mushy foods because they were likely to make us ill (due to rotting) and decreased our odds of survival. This developed into a preference for crunchy foods, which signaled freshness. Now scientists have isolated the optimum decibel range, which is thought to be produced by about 100 tiny cell bursts, that creates the most desirable sound between our teeth."

Next: Does your mouth water when you think about food?

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