Food preservation refers to any one of a number of techniques used to prevent food from spoiling. All foods begin to spoil as soon as they are harvested or slaughtered. Some spoiling is caused by such microorganisms as bacteria and mold. Other spoilage results from chemical changes within the food itself due to natural processes such as enzyme action or oxidation.
Ages-old food preservation techniques include drying, smoking, cooling, freezing, fermenting, salting, pickling, and canning.
Drying and smoking. One of the most ancient methods of food preservation is sun- or air-drying. Drying works because it removes much of the food's water. Without adequate water, microorganisms cannot multiply and chemical activities greatly slow down. Dried meat was one of the earliest staple foods of hunters and nomads (people who constantly moved about). Once fire was discovered, prehistoric cave dwellers heat-dried meat and fish, which probably led to the development of smoking as another way to preserve these foods. The Phoenicians of the Middle East air-dried fish. Ancient Egyptians stockpiled dried grains. Native North Americans produced a nutritious food called pemmican by grinding together dried meat, dried fruit, and fat.
Cooling and freezing. Early northern societies quickly learned that coolness as well as freezing helped preserve foods. Microbe growth and chemical changes slow down at low temperatures and completely stop when water is frozen. Pre-Columbian natives in Peru and Bolivia freeze-dried potatoes, while the early Japanese and Koreans freeze-dried their fish. Water evaporating through earthenware jars was used as a coolant in 2500 B.C. by Egyptians and East Indians. Ancient Chinese, Greeks, and Romans stored ice and mountain snow in cellars or icehouses to keep food cool.
Fermenting. Fermentation was particularly useful for people in southern climates, where cooling and freezing were not practical. When a food ferments, it produces acids that prevent the growth of organisms that cause spoilage. Grapes, rice, and barley were fermented into wine and beer by early people. Fermentation also was used to produce cheese and yogurt from milk.
Salting and pickling. Salting, which also inhibits bacteria growth, was a preferred method of preserving fish as early as 3500 B.C. in the Mediterranean world, and also was practiced in ancient China.
Substances besides salt were found to slow food spoilage. The Chinese began using spices as preservatives around 2700 B.C. Ancient Egyptians used mustard seeds to keep fruit juice from spoiling. Jars of fruit preserved with honey have been found in the ruins of Pompeii, Italy. Melted fat—as Native North Americans discovered with pemmican—preserved meat by sealing out air. Pickling—preserving foods in an acid substance like vinegar—also was used during ancient times.
Early canning. By the Middle Ages (400–1450), all of these ancient methods of preserving foods were widely practiced throughout Europe and Asia, often in combination. Salted fish became the staple food of poor people during this time—particularly salted herring, introduced in 1283 by Willem Beukelszoon of Holland. As the modern era approached, the Dutch navy in the mid-1700s developed a way of preserving beef in iron cans by packing it in hot fat and then sealing the cans. By the late 1700s, the Dutch also were preserving cooked, smoked salmon by packing it with butter or olive oil in sealed cans.
Modern methods of food preservation include canning, mechanical refrigeration and freezing, the addition of chemicals, and irradiation.
Additive: A chemical compound that is added to foods to give them some desirable quality, such as preventing them from spoiling.
Antioxidant: A chemical compound that has the ability to prevent the oxidation of substances with which it is associated.
Dehydration: The removal of water from a material.
Fermentation: A chemical reaction in which sugars are converted to organic acids.
Irradiation: The process by which some substance, such as a food, is exposed to some form of radiation, such as gamma rays or X rays.
Oxidation: A chemical reaction in which oxygen reacts with some other substance.
With the Industrial Revolution (1760–1870), populations became concentrated in ever-growing cities and towns. Thus other methods were needed to preserve food reliably for transportation over long distances and for longer shelf life.
The crucial development was the invention of sophisticated canning techniques during the 1790s by the Frenchman Nicolas François Appert (1750–1841), who operated the world's first commercial cannery in 1804. Appert's method, which first used bottles, was greatly improved by the 1810 invention of the tin can in England. Used at first for Arctic expeditions and by the military, canned foods came into widespread use among the general population by the mid-1800s.
Packaged frozen foods. The 1851 invention of a commercial icemaking machine by American John Gorrie (1803–1855) led to the development of large-scale commercial refrigeration of foods for shipping and storage. Clarence Birdseye (1886–1956) introduced tasty quick-frozen foods in 1925. Shortages of canned goods after World War II (1939–45) helped boost the popularity of frozen foods.
Dehydrated foods. Modern methods of drying foods began in France in 1795 with a hot-air vegetable dehydrator. Dried eggs were widely sold in the United States after 1895, but dried food was not produced in volume in the United States until it was used by soldiers during World War I (1914–18). World War II led to the development of dried skim milk, potato flakes, instant coffee, and soup mixes. After the war, freeze-drying was applied to items such as coffee and orange juice, and the technique continues to be applied to other foodstuffs today.
Chemicals, sterile packages, and irradiation. Chemicals are now commonly added to food to prevent spoilage. They include benzoic acid, sorbic acid, and sulfur dioxide. Antioxidants such as BHA (butylated hydroxyanisole) and ascorbic acid (vitamin C) prevent compounds in food from combining with oxygen to produce inedible changes. The use of chemical additives has not been without controversy. The spread of often unnecessary and sometimes harmful chemical additives to food during the late 1800s led to governmental regulation in both England and the United States.
Aseptic packaging is a relatively new way to keep food from spoiling. A food product is sterilized and then sealed in a sterilized container. Aseptic packages, including plastic, aluminum foil, and paper, are lighter and cheaper than the traditional metal and glass containers used for canning. Aseptically processed foods are also sterilized much more quickly, so their flavor is better. Aseptic packaging became commercially available in 1981. However, controversy has developed about the amount of disposable containers produced by this method.
Food irradiation uses low doses of radiation to kill microorganisms in food and to extend the amount of time in which food can be sold and eaten safely. Strawberries that are treated with irradiation can last for up to two weeks, compared to less than a week for untreated berries. The process, which remains controversial, is a relative newcomer among food-preserving techniques. The U.S. government first approved its use on fresh fruits and vegetables in 1986 and for poultry in 1990.