Understanding how we chew our food will change how we think about cooking.
DR. JOHN HARVEY KELLOGG, he of the breakfast cereals, advocated a hygienic regime based on relentless mastication. His ideas echoed an ancient East Asian tradition according to which each mouthful of whole-grain rice was to be chewed 100 times.
Why do we chew in the first place? Everyone knows that mastication breaks up food into smaller pieces—small enough that, having also been lubricated by saliva, they easily descend into the digestive system. Jons Prinz and Peter Lucas at the Odontological Museum in London have identified another function. Without knowing it, we chew until particles of food are bound together by saliva into a compact mouthful that can be swallowed in such a way as to minimize the risk that small bits take a wrong turn down into the windpipe. For each food, then, there is an optimal number of masticatory movements.
In asserting that “animals feed, man eats,” Brillat-Savarin sought to do away with the animal side of our nature—the very thing that upset the Précieuses of mid–seventeenth-century salons in Paris, who made a fashion of mousses because they eliminated the need for “the unsightly act of mastication.” And yet who wants to forgo the pleasures of a piece of crusty bread? A sticky dumpling? A crispy piece of bacon? If we are to enjoy the full range of pleasures that the culinary world offers, we must frankly accept our humanity and turn our physiological peculiarities to the advantage of our weakness for good food.
Chewing divides food into pieces of smaller diameter than that of our pharynx. Nonetheless, we normally go well beyond what is necessary for this purpose. As mammals that expend a great deal of energy, we chew our food in order to increase the surface area accessible to digestive enzymes. Indirectly, then, mastication accelerates the assimilation of nourishment.
Prinz and Lucas devised a model to explain how salivation causes the particles formed by chewing to cohere. Their model takes into account the two main forces exerted on masticated food: adhesion between its parts and the adhesion of these parts to the inside of the mouth. These forces depend on the secretion of saliva and the quantity of juice squeezed out of food by the act of chewing.
Small pieces of food are broken up less thoroughly than big pieces. On the other hand, the number of fragments into which a mouthful of food is divided by chewing depends on the mechanical characteristics of the food in question. To simplify the modeling problem, the British physiologists assumed that each piece of food is divided into spherical particles and calculated the total surface forces holding them together.
Furthermore, Prinz and Lucas assumed that these particles agglomerate when the force causing them to adhere to one another is greater than the force causing them to adhere to the wall of the mouth. Using computer calculations of these forces and incorporating values for various other parameters drawn from studies of human physiology, they then determined the cohesion of mouthfuls of food after 150 masticatory cycles for two foods having very different properties: raw carrots, which are broken up very slowly, and Brazil nuts, which are broken up much more rapidly. Computation showed that the cohesion of the masticated food is initially low, then rapidly increases and reaches its highest point after twenty cycles. After that point it diminishes as the particles become smaller and smaller.
To test the proposed model, the calculated degree of cohesion was compared with the cohesion actually measured in mouthfuls of food spit out after having been chewed. The agreement of theory with practice was good, but the actual number of masticatory cycles was a bit higher than the number calculated, no doubt because we are not only machines for absorbing nourishment: “The Creator, in making man eat in order to live,” Brillat-Savarin observed, “persuaded him by appetite and rewarded with by pleasure.” Because we take pleasure in eating, we prolong our enjoyment by chewing longer than is strictly necessary in order to make food particles cohere.
Model and Cuisine
What can we learn from the model for culinary purposes? Depending on their physical characteristics, foods need a greater or lesser degree of mastication. The addition of compounds that make saliva more liquid (tannins, for example) or increase the concentration of liquids extracted by the teeth has the effect of reducing cohesion, which ought to lengthen the amount of time spent chewing and so add to the enjoyment one takes from a dish. Could this be why gourmets drink wine (which contains tannins) with their meals?
Thickening agents, on the other hand, ought to accelerate the absorption of food into the digestive system. The use of such agents, particularly in diet products, creates a marketing problem: The shorter the time that food is chewed, the fewer the number of odorant and taste molecules that are released.
More generally, the hypothesis that the body automatically detects the ideal cohesion of mouthfuls of food ought to be a source of fresh ideas for the cook who wants to find new ways to combine sticky, gluey, dry, or absorbent ingredients.