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Crushing

CRUSHING

CRUSHING. Crushing refers to the pressing, grinding, or pounding of an item into smaller particles, a powder, or a paste. The largest of the human teeth, the molars, are designed for crushing food into small particles that can be swallowed and digested. Digestion is enhanced by the breaking of food into small particles that expose more food surface to the action of digestive enzymes; the more food surface exposed, the more efficient the process of digestion.

The crushing of cereal grains (wheat, corn, rye, buckwheat, rice) into flour is a good example of the use of tools to reduce particle size. The flour can then be eaten raw, cooked with water into porridge, or moistened, formed into a loaf, and baked as bread. Another nutritional advantage of flour over the whole grain is that the flour can be sifted to remove the bran fraction, which is largely cellulose and indigestible. The germ fraction of the kernel is typically removed with the bran and hence considerably reduces the nutritional values of the flour in terms of protein, vitamins, and minerals. Flours, rather then whole grains, also have the advantage of cooking faster and can be used to make gruels that are useful for feeding infants and the elderly, who have a limited ability to chew foods into small particles.

A number of devices have been used to crush grains into flours. The Australian Aborigines used a simple wooden mortar and stone pestle to roughly crush grass seed, which they used a make bread, or damper. The ancient Egyptians developed a mill made of two circular stones to crush wheat into flour; modern mills operate on the same principle. Traditional peoples in Mesoamerica used a stone mortar and pestle to crush presoaked corn kernels into a wet mash to make tortillas. Foods with hard, inedible shells are crushed to facilitate removal of the shell and extraction of the edible component. Examples are hard-shelled nuts like walnuts and shellfish like lobsters. The devices used are tools like hammer-stones and metal pliers.

Other foods are crushed to extract a component of the food from the more fibrous matrix of the whole food. Seeds and palm fruits are crushed to extract the oil. Grapes and other soft fruits, as well as sugarcane, a tall grass, are crushed to extract the juice. Oils and juice tend to be more readily digested than the whole food. Also, the liquid can be added to other foods to improve their energy content and hence the energy content of the diet. This is especially important in rootcrop-and tuber-based diets, which are typically low in energy density.

The tools used in crushing foods vary with the foods themselves and level of technology. Grapes are crushed gently to avoid damaging the seed that can release bitterness into the wine. They were traditionally crushed by workers' treading on them or with wooden paddles. Olives are crushed to separate the pit from the pulp and the latter then pressed to extract the liquids. For the initial step the Romans used a roller-mill (trapeta ), designed to ensure that the olive pit itself would not be damaged. Sugarcane was crushed historically in South America by squeezing the cane through a set of rollers (trapiche ). The juice was then boiled to evaporate the water and the concentrated sugar allowed to crystallize.

Still other foods are crushed to achieve a particular texture in the preparation of certain dishes. In Hawaii, cooked taro corms (enlarged portion of the plant stem) are crushed to a smooth paste and then pounded in a mortar and pestle to make the famous poi. In Africa, cassava roots are left to soak and ferment in water and then crushed into dough that is molded into loaves and sun dried. Cooked yams are crushed with water to form soft dough called fufu in Ghana. In the highlands of Peru cooked potatoes are crushed on a grinding stone and then added to water or broth to make a thick soup or masamora. In Europe and North America, cooked potatoes are crushed to a soft uniform mass to make mashed potatoes. Nuts and meat are crushed into pastes to make sandwich spreads like peanut butter and potted meats or pâté.

In a number of different cuisines, spices are crushed to stimulate the release of flavor. In India, spices are ground in a mortar and pestle. In Mexico, spices were traditionally crushed to a paste with chili peppers using the same grinding stone (mano and metate ) used for grinding maize, or in a stone bowl made from lava stone. Garlic, a flavoring agent, is also often crushed before being added to food. In all cases flavor enhancement and flavor release are the goals of the cook, but the crushing should also facilitate digestion.

Crushing is also used to meld two or more foods together. A classic example is the pemmican traditionally made by North American Indians. Pemmican is dried meat and animal fat pounded into a paste and preserved in the form of pressed cakes. A less well-known example is "desert fruitcake," a cake made of crickets pounded together with berries. Another example is kibbeh, a Lebanese dish made by pounding lamb and cracked wheat together in a stone mortar until they form a paste and seasoning the mix with mint and pine nuts. The resulting mix is rolled into sausage-like forms and cooked in oil or eaten raw.

See also Combination of Proteins; Dietary Assessment; Preparation of Food; Rice; Wheat.

BIBLIOGRAPHY

Davidson, Alan. The Oxford Companion to Food. Oxford: Oxford University Press, 1999.

Kimball, Yeffe, and Jean Anderson. The Art of American Indian Cooking. New York: Doubleday, 1965.

Kuper, Jessica, ed. The Anthropologists' Cookbook. New York: Universe Books, 1977.

Nickles, Harry G. Middle Eastern Cooking. New York: Time-Life Books, 1969.

Toussaint-Samat, Maguelonne. History of Food. Translated by Anthea Bell. Cambridge, Mass.: Blackwell, 1992. Original edition: Histoire naturelle et morale de la nourriture. Paris: Bordas, 1987.

Whitney, Eleanor N., and Sharon R. Rolfes. Understanding Nutrition. 8th ed. Belmont, Calif.: Wadsworth, 1999.

Darna L. Dufour

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crushing

crushing In mineral processing, the breaking up of large particles by compression between two surfaces. Primary crushing produces pieces 100–50 mm in diameter; secondary crushing reduces those to 10mm.

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