If you said something like, “To make it small enough to swallow,” you just might be wrong…if biophysics research proves right.
That research, mentioned in a recent article on physicsworld.com, a site from the Institute of Physics, showed that it’s not so much to make the food small as it is to make it swallowable. Researchers Jon Prinz and Peter Lucas
pointed out that when mammals swallow, food passes over the airway on its way to the stomach, so there is a potentially fatal risk of choking if stray food particles go down the wrong way. They suggested, therefore, that chewing allows us to press our food into a firm blob – technically known as a bolus – at the top of our mouth with our tongue. It can then be safely swallowed.
To test this idea, they got volunteers to eat diced carrots and nuts, counting the number of times the subjects chewed the food before swallowing it. They then modelled the cohesive strength of the bolus after different numbers of chews, by calculating the viscous forces needed to separate the ever-smaller particles. They found that for both foods, the bolus strength initially increased with the number of chews, because the smaller particles had a greater surface area, meaning that the bolus was held together by increased viscous forces. As chewing progressed, however, more saliva was pressed into the bolus, which eventually increased the distance between the particles, thus reducing viscous forces and weakening the bolus. Left to chew their food naturally, unencumbered by prying researchers, people swallowed the bolus at around the time when it was strongest – more support for Prinz and Lucas’s theory.
To learn about a few other such “mysteries” – Why do we have notched teeth? Why do we have fingerprints? – check out the whole article, “How People Work.”