Some techniques of food preservation pre-date the
dawn of agriculture. Others were discovered more recently.
Boiling Boiling liquids can kill any existing microbes. Milk and water are often boiled to kill any harmful microbes that may be present in them.
Burial Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool temperatures, pH level, or
desiccants in the soil. Burial may be combined with other methods such as salting or fermentation. Most foods can be preserved in soil that is very dry and salty (thus a desiccant) such as sand, or soil that is frozen. Many
root vegetables are very resistant to spoilage and require no other preservation than storage in cool dark conditions, for example by burial in the ground, such as in a
storage clamp (not to be confused with a
root cellar). Cabbage was traditionally buried during autumn in northern US farms for preservation. Some methods keep it crispy while other methods produce
sauerkraut. A similar process is used in the traditional production of
kimchi. Sometimes meat is buried under conditions that cause preservation. If buried on hot coals or ashes, the heat can kill pathogens, the dry ash can desiccate, and the earth can block oxygen and further contamination. If buried where the earth is very cold, the earth acts like a refrigerator, or, in areas of
permafrost, a freezer. In
Odisha, India, it is practical to store rice by burying it underground. This method helps to store for three to six months during the dry season. Butter and similar substances have been preserved as
bog butter in Irish
peat bogs for centuries.
Century eggs are traditionally created by placing eggs in alkaline mud (or other alkaline substance), resulting in their "inorganic" fermentation through raised pH instead of spoiling. The fermentation preserves them and breaks down some of the complex, less flavorful proteins and fats into simpler, more flavorful ones.
Canning Canning involves cooking food, sealing it in sterilized cans or jars, and
boiling the containers to kill or weaken any remaining bacteria as a form of
sterilization. It was invented by the French confectioner
Nicolas Appert. By 1806, this process was used by the French Navy to preserve meat, fruit, vegetables, and even milk. Although Appert had discovered a new way of preservation, it was not understood until 1864 when
Louis Pasteur found the relationship between microorganisms, food spoilage, and illness. The preparation will keep longer if stored in a cold cellar or buried in cold ground.
Cooling Cooling preserves food by slowing down the growth and reproduction of microorganisms and the action of enzymes that causes the food to rot. The introduction of commercial and domestic refrigerators drastically improved the diets of many in the
Western world by allowing food such as fresh fruit, salads and dairy products to be stored safely for longer periods, particularly during warm weather. Before the era of mechanical refrigeration, cooling for food storage occurred in the forms of
root cellars and
iceboxes. Rural people often did their own
ice cutting, whereas town and city dwellers often relied on the
ice trade. Today, root cellaring remains popular among people who value various goals, including
local food,
heirloom crops, traditional home
cooking techniques,
family farming,
frugality,
self-sufficiency,
organic farming, and others.
Curing " or "pink salt". It is typically a combination of salt and sodium nitrite, with the pink color added to distinguish it from ordinary salt. Curing is any of various food preservation and flavoring processes of foods such as meat, fish and vegetables, by the addition of
salt, with the aim of drawing moisture out of the food by the process of
osmosis. Because curing increases the
solute concentration in the food and hence decreases its
water potential, the food becomes inhospitable for the
microbial growth that causes
food spoilage.
Smoking and
salting techniques improve on the drying process and add antimicrobial agents that aid in preservation. Smoke deposits a number of pyrolysis products onto the food, including the
phenols
syringol,
guaiacol and
catechol. Salt accelerates the drying process using
osmosis and also inhibits the growth of several common strains of bacteria. More recently
nitrites have been used to cure meat, contributing a characteristic pink colour. In 2015, the
International Agency for Research on Cancer of the
World Health Organization classified
processed meat—i.e., meat that has undergone salting, curing, and smoking—as "carcinogenic to humans".
Drying drying in the Sun The earliest form of curing is drying, which has been in use since ancient times, the earliest known practice dates back to 12,000 B.C. by inhabitants of the modern Asian and Middle Eastern regions. Water is traditionally removed through
evaporation by using methods such as air drying, sun drying, smoking or wind drying, although today electric
food dehydrators can be used to speed the drying process and ensure more consistent results.
Fermentation Some foods, such as many
cheeses,
wines, and
beers, are prepared by fermentation. This involves cultivating specific
microorganisms to combat spoilage from other, less benign organisms. These microorganisms keep pathogens in check by producing acid or alcohol, which eventually creates an environment toxic for themselves and other microorganisms. Methods of fermentation include, but are not limited to, starter microorganisms, salt, hops, controlled (usually cool) temperatures and controlled (usually low) levels of oxygen. These methods are used to create the specific controlled conditions that will support the desirable organisms that produce food fit for human consumption. Fermentation is the microbial conversion of starch and sugars into alcohol. Not only can fermentation produce alcohol, but it can also be a valuable preservation technique. Fermentation can also make foods more nutritious and palatable. Water was also turned into alcoholic beverages through fermentation. When water is used to make beer, the boiling during the brewing process may kill bacteria that could make people sick. The barley and other ingredients also infuse the drink with nutrients, and the microorganisms can also produce vitamins as they ferment.
Freezing Freezing is also one of the most commonly used processes, both commercially and domestically, for preserving a very wide range of foods, including prepared foods that would not have required freezing in their unprepared state. For example, potato waffles are stored in the freezer, but potatoes themselves require only a cool dark place to ensure many months' storage. Cold stores provide large-volume, long-term storage for strategic food stocks held in case of national emergency in many countries.
Heating Heating to temperatures which are sufficient to kill microorganisms inside the food is a method used with
perpetual stews.
Jellying Food may be preserved by cooking in a material that solidifies to form a gel. Such materials include
gelatin,
agar,
maize flour, and
arrowroot flour. Some animal flesh forms a protein gel when cooked.
Eels and elvers, and
sipunculid worms, are a delicacy in
Xiamen, China, as are
jellied eels in the
East End of London, where they are eaten with mashed potatoes.
British cuisine has a rich tradition of
potted meats. Meat off-cuts were, until the 1950s, preserved in
aspic, a gel made from gelatin and clarified meat broth. Another form of preservation is setting the cooked food in a container and covering it with a layer of fat. Potted chicken liver can be prepared in this way, and so can
potted shrimps, to be served on toast.
Calf's foot jelly used to be prepared for invalids. Jellying is one of the steps in producing traditional
pâtés. Many
jugged meats (see below) are also jellied. Another type of jellying is
fruit preserves, which are preparations of cooked fruits, vegetables and sugar, often stored in glass jam jars and
Mason jars. Many varieties of fruit preserves are made globally, including sweet fruit preserves, such as those made from strawberry or apricot, and savory preserves, such as those made from tomatoes or squash. The ingredients used and how they are prepared determine the type of preserves;
jams,
jellies, and
marmalades are all examples of different styles of fruit preserves that vary based upon the fruit used. In English, the word
preserves, in plural form, is used to describe all types of jams and jellies.
Jugging Meat can be preserved by jugging. Jugging is the process of
stewing the meat (commonly
game or
fish) in a covered
earthenware jug or
casserole. The animal to be jugged is usually cut into pieces, placed into a tightly sealed jug with brine or
gravy, and stewed.
Red wine and/or the animal's own blood is sometimes added to the cooking liquid. Jugging was a popular method of preserving meat up until the middle of the 20th century.
Kangina In rural
Afghanistan, grapes are preserved in disc-shaped vessels made of mud and straw, called
kangina. The vessels, which can preserve fresh grapes for up to 6 months, passively control their internal environments to restrict gas exchange and water loss, prolonging the lives of late-harvested grapes stored within them.
Lye Sodium hydroxide (
lye) makes food too
alkaline for bacterial growth. Lye will
saponify fats in the food, which will change its flavor and texture.
Lutefisk uses lye in its preparation, as do some olive recipes. Modern recipes for
century eggs also call for lye.
Pickling Pickling is a method of preserving food in an edible, antimicrobial liquid. Pickling can be broadly classified into two categories: chemical pickling and fermentation pickling. In chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other microorganisms. Typical pickling agents include
brine (high in salt),
vinegar,
alcohol, and
vegetable oil. Many chemical pickling processes also involve heating or boiling so that the food being preserved becomes saturated with the pickling agent. Common chemically pickled foods include
cucumbers,
peppers,
corned beef,
herring, and
eggs, as well as mixed vegetables such as
piccalilli. In fermentation pickling, bacteria in the liquid produce
organic acids as preservation agents, typically by a process that produces
lactic acid through the presence of
lactobacillales. Fermented pickles include
sauerkraut,
nukazuke,
kimchi, and
surströmming.
Sugaring The earliest cultures have used
sugar as a preservative, and it was commonplace to store fruit in honey. "Sugar tends to draw water from the microbes (plasmolysis). This process leaves the microbial cells dehydrated, thus killing them. In this way, the food will remain safe from microbial spoilage." Sugar is used to preserve fruits, either in an
antimicrobial syrup with fruit such as apples, pears, peaches, apricots, and plums, or in crystallized form where the preserved material is cooked in sugar to the point of crystallization and the resultant product is then stored dry. The latter method is used for the skins of
citrus fruit (candied peel),
angelica, and
ginger. == Modern industrial techniques ==