Beaumont observed the stomach closely. He noted how quiet it was when it had no food, the rugae (muscle folds) nestled upon each other. When soup was swallowed, the stomach was at first slow to respond. “The rugae gently close upon it, and gradually diffuse it through the gastric cavity.” When Beaumont placed food directly on the stomach wall, the stomach became excited and its color brightened. There was a “gradual appearance of innumerable, very fine, lucid specks, rising through the transparent mucous coat, and seeming to burst, and discharge themselves upon the very points of the papillae, diffusing a limpid, thin fluid over the whole interior gastric surface.” For the first time, it was possible to watch digestion in action.
Beaumont continued his experiments intermittently for eight years. He recorded in detail how long it took foods to be digested by the stomach and emptied into the duodenum. From those observations he drew two conclusions relevant to the effects of cooking.
The more tender the food, the more rapidly and completely it was digested. He noted the same effect for food that was finely divided. “Vegetable, like animal substances, are more capable of digestion in proportion to the minuteness of their division . . . provided they are of a soft solid.” Potatoes boiled to reduce them to a dry powder tasted poor, but they were more easily digested. If not powdered, entire pieces remained long undissolved in the stomach and yielded slowly to the action of the gastric juice. “The difference is quite obvious on submitting parcels of this vegetation, in different states of preparation, to the operation of the gastric juice, either in the stomach or out of it.”
The same principles held, said Beaumont, with respect to meat. “Fibrine and gelatine [muscle fibers and collagen in meat] are affected in the same way. If tender and finely divided, they are disposed of readily; if in large and solid masses, digestion is proportionally retarded. . . . Minuteness of division and tenderness of fibre are the two grand essentials for speedy and easy digestion.”
In addition to “minuteness of division and tenderness,” cooking helped. He was explicit in the case of potatoes. “Pieces of raw potato, when submitted to the operation of this fluid, in the same manner, almost entirely resist its action. Many hours elapse before the slightest appearance of digestion is observable, and this only upon the surface, where the external laminae become a little softened, mucilaginous, and slightly farinaceous. Every physician who has had much practice in the diseases of children knows that partially boiled potatoes, when not sufficiently masticated (which is always the case with children), are frequently a source of colics and bowel complaints, and that large pieces of this vegetable pass the bowels untouched by digestion.” It was the same with meat. When Beaumont introduced boiled beef and raw beef at noon, the boiled beef was gone by 2 P.M. But the piece of raw, salted, lean beef of the same size was only slightly macerated on the surface, while its general texture remained firm and intact.
Sadly, St. Martin came to resent being a focus of scientific interest. By the time of his death in 1880 at the ripe old age of eighty-five, he felt thoroughly mistreated. He had long refused to have anything to do with Beaumont, and his family shared his sense of abuse. Dr. William Osler, often described as the father of modern medicine, hoped to study St. Martin’s body and even buy his stomach, but the family refused. They kept his body privately for four days to ensure that it rotted, then they buried him in an unusually deep grave, eight feet down, to thwart any medical interest in his organs.
Beaumont’s discovery that soft and finely divided foods are more easily digested conforms to our preference for such items. In 2006 the London department store Selfridges received five advance orders for a new product: the world’s most expensive sandwich. For £85 ($148) people had the chance to eat a 595-gram (21-ounce) mixture of fermented sourdough bread, Wagyu beef, fresh lobe foie gras, black truffle mayonnaise, brie de Meaux, English plum tomatoes, and confit. The beef explains the high price. Wagyu cattle are one of the most expensive breeds in the world because their meat is exceptionally tender, and no effort is spared to make it so. The animals are raised on a diet that includes beer and grain, and their muscles are regularly massaged with sake, the Japanese rice wine. The fat in the meat is claimed to melt at room temperature. The exceptional value of Wagyu beef illustrates a notable human pattern: people like their meat tender. “Of all the attributes of eating quality,” wrote meat scientist R. A. Lawrie, “texture and tenderness are presently rated most important by the average consumer, and appear to be sought at the expense of flavour and colour.” A key aim of meat science is to discover how to produce the most tender meat. Rearing, slaughtering, preservation, and preparation methods all play their part.
So does cooking. According to cooking historian Michael Symons, the cook’s main goal has always been to soften food. “The central theme is that cooks assist the bodily machine,” he wrote. He cited
Mrs. Beeton’s Book of Household Management
, which in 1861 sought to advise naive housewives about the fundamentals of the kitchen. The first of six reasons for cooking was “to render mastication easy.” “Hurrying over our meals, as we do, we should fare badly if all the grinding and subdividing of human food had to be accomplished by human teeth.” A second reason for cooking stressed the point Beaumont had discovered: “to facilitate and hasten digestion.”
The way Kalahari San hunter-gatherers prepare their food suggests a similar concern for making their meals as soft as possible. They cook their meat until “it is so tender that the sinews will fall apart.” Then “it is usually crushed in a mortar.” It is the same with plant foods. After melons or seeds have been cooked by burying them in hot embers or ashes, their contents are “ground in a mortar and eaten as a gruel.”
Tropical and subtropical hunter-gatherers, such as Andaman Islanders, Siriono, Mbuti, and Kalahari San, eat all their meat cooked. It is in cooler climates that people sometimes eat animal protein raw. If they are eaten uncooked, the raw items tend to be soft, like the mammal livers and rotten fish the Inuit eat. The island-living Yahgan in the south of Tierra del Fuego have three such foods, according to Martin Gusinde, who lived with them for twenty years. There is “the soft meat” of mollusks such as winkles, “squeezed out of the calcareous shell with a slight pressure of the fingers and eaten without any preparation, except that occasionally the little morsel of fish is dipped into seal blubber.” There are also the ovaries of sea urchins and the milky liquid in the shell, a delicacy shared by the Tlingit and eaten by Japanese and Europeans today in fine restaurants. According to Gusinde, a few individuals found the raw fat of a young whale tasty. Other than these cases, all animal protein was cooked.
Game animals have a few soft parts. The Utes of Colorado were said to roast all their meat but they ate the kidneys and livers raw. Australian aborigines supposedly eat mammal intestines raw on occasion, as Inuit do with fish and birds. Raw intestines may seem a startling preference in view of the potential for parasites to be present. They are likewise almost always the first part of a prey animal eaten by chimpanzees, chewed and swallowed much faster than muscle meat.
Raw-blood meals are well known among pastoralists such as Maasai, and as we saw in chapter 1, reported by Marco Polo in thirteenth-century Mongol nomad warriors. Elsewhere raw-fat meals are provided by fat-tailed sheep. Asian nomads value these sheep so highly and have bred them to such an extreme that they sometimes provide their animals with little carts to support the massive tail. On trek the nomads remove some of the fat for a raw meal, and the sheep travels a little lighter the next day.
While some foods are naturally tender, meat is variable. Meat with smaller muscle fibers is more tender, so chicken is more tender than beef. An animal slaughtered without being stressed retains more glycogen in its muscles. After death the glycogen converts to lactic acid, which promotes denaturation and therefore a more tender meat. Carcasses that are left to hang for several days are more tender, because proteins are partly broken down by enzymes.
But nothing changes meat tenderness as much as cooking because heat has a tremendous effect on the material in meat most responsible for its toughness: connective tissue. Composed of a fibrous protein called collagen and a stretchy one called elastin, connective tissue wraps the meat in three pervasive layers. The innermost layer is a sleeve called endomysium, which surrounds each individual muscle fiber like the skin of a sausage. Bundles of endomysium-enclosed muscle fibers lie alongside one another jointly sheathed in a larger skin, the perimysium. Finally, those bundles, or fascicles, are held together by the outer wrapping, or epimysium, which encloses the entire muscle. At the end of the muscle, the epimysium turns into the tendon. Connective tissue is slippery, elastic, and strong: the tensile strength of tendons can be half that of aluminum. So connective tissue not only does a wonderful job of keeping our muscles in place but it also makes meat very difficult to eat, particularly for an animal like humans or chimpanzees whose teeth are notably blunt.
The main protein in connective tissue, collagen, owes its toughness to an elegant repeating structure. Three left-handed helices of protein twirl around one another to form a right-handed superhelix. The superhelixes join into fibrils, and the fibrils form fibers that assemble into a crisscross pattern. The effect is a marvel of microengineering. The extraordinary mechanical strength of collagen explains why sinews, or tendons, make excellent bowstrings and why it is the most abundant protein in vertebrates: it is the main component of skin.
But collagen has an Achilles’ heel: heat turns it to jelly. Collagen shrinks when it reaches its denaturation temperature of 60-70
o
C (140-158
o
F), and then, as the helices start to unwind, it starts melting away. Whether heated about 100
o
C (212
o
F) for a short time or at lower temperatures for a longer time, the fibrils of collagen fall apart until they convert into the very antithesis of toughness: gelatin, a protein with commercial uses from Jell-O to jellied eels. The amount of force required to cut through a standard piece of meat tends to reach a minimum between 60
o
C and 70
o
C (140 and 158
o
F). Above those temperatures, slow cooking in water can sometimes continue to increase the tenderness.
Unfortunately for the amateur cooks among us, a second effect of heating meat is contrary to the first. Unlike connective tissue, heated muscle fibers tend to get tougher and drier. The cumulative effects of cooking meat are therefore complex. Bad cooking can render meat hard to chew, but good cooking tenderizes every kind of meat, from shrimp and octopus to rabbit, goat, and beef. Tenderness is even important for cooks preparing raw meat. Steak tartare requires a particularly high grade of meat (low in connective tissue) and the addition of raw eggs, onions, and sauces. The
Joy of Cooking
recommends grinding top sirloin, or scraping it with the back of a knife, until only the fibers of connective tissue remain.
Steak tartare supposedly gets its name from the Tartars, or Mongols, who rode in Genghis Khan’s army. When soldiers were moving too fast to cook, they sometimes drank horse blood but they were also reported to put slabs of meat under the saddles, riding on them all day until they were tender. Brillat-Savarin recorded an enthusiastic testimony of the practice: “Dining with a captain of Croats in 1815, ‘Gads,’ said he, ‘there’s no need of so much fuss in order to have a good dinner! When we are on scout duty and feel hungry, we shoot down the first beast that comes in our way, and cutting out a good thick slice, we sprinkle some salt over it, place it between the saddle and the horse’s back, set off at a gallop for a sufficient time, and’ (working his jaws like a man eating large mouthfuls) ‘
gniaw, gniaw, gniaw
, we have a dinner fit for a prince.’”
Why does tenderness matter? Beaumont observed that softer food was digested faster, and since faster or easier digestion demands less metabolic effort, softer food might lead to energy saved during digestion. The idea should make sense when you consider the greater liveliness you feel after eating a light meal compared to a heavy one: the light meal demands less work from your intestines and therefore makes other kinds of physical activity easy. This energy-saving principle has been beautifully shown in rats given soft food.
A team of Japanese scientists led by Kyoko Oka reared twenty rats on two different food regimes. Ten rats ate ordinary laboratory pellets, which were hard enough to require substantial chewing. The other ten ate a version of the standard food that was modified in a single way: the pellets were made softer by increasing their air content. The soft pellets were puffed up like a breakfast cereal and required only half the force of the hard pellets to crush them. In every other way the rats’ conditions were identical. The calorie intake, and calorie expenditure on locomotion, were found to be the same for the two groups. The ordinary and soft pellets did not differ in how much they had been cooked, their nutrient composition, or water content. Conventional theory based on the calculation of calorie intake would predict that the two groups of rats should have grown at the same rates and to the same size. They should have had the same body weight and the same levels of fat.
But they did not. The rats began eating their different pellet diets at four weeks old. By fifteen weeks the growth curves of the two groups had visibly separated, and by twenty-two weeks the group curves were significantly different. The rats eating soft food slowly became heavier than those eating hard food: on average, 37 grams heavier, or about 6 percent; and they had more abdominal fat: on average, 30 percent more, enough to be classified as obese. Soft, well-processed foods made the rats fat. The difference was in the cost of digestion. At every meal the rats experienced a rise in body temperature, but the rise was lower in the soft-pellet group than in the hard-pellet group. The difference was particularly strong in the first hour after eating, when the stomach was actively churning and secreting. The researchers concluded that the reason the softer diet led to obesity was simply that it was a little less costly to digest.