Food preservation prevents the growth of microorganisms (such as yeast), or other microorganisms (although some methods work by introducing benign bacteria or fungi to the food), as well as slowing the oxidation of fats that cause rancidity. Food preservation may also include processes that inhibit visual deterioration, such as the enzymatic browning reaction in apples after they are cut during food preparation.
Many processes designed to preserve food involves more than one food preservation method. Preserving fruit by turning it into jam, for example, involves boiling (reduce the fruit’s moisture content and to kill bacteria etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination).
Some traditional methods of preserving food have been shown to have a lower energy input and carbon footprint, when compared to modern methods. Some methods of food preservation are known to create carcinogens. 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, fermenting, and smoking, as “carcinogenic to humans”
New techniques of food preservation became available to the home chef from the dawn of agriculture until the industrial Revolution
Bag of Prague powder #1, also known as “curing salt” or “pink salt”. It is typically a combination of salt and sodium nitrite, with the pink color added to distinguish it from ordinary salt
The earliest form of curing was dehydration or drying. Used as early as 12,000 BC. 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 color.
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 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.
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.
Boiling liquid food items can kill any existing microbes. Milk and water are often boiled to kill any harmful microbes that may be present in them.
Heating to temperatures which are sufficient to kill microorganisms inside the food is a method used with perpetual stews. Milt is also boiled before to kill many microorganisms.
The earliest cultures have used sugar so a preservative, and it was commonplace to store fruit in honey. Similar to pickled foods, sugar cane was brought to Europe through the trade routes. In northern climates without sufficient sun to dry foods, preserves are made by heating the fruit with sugar. Sugars trends 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. This method is used for the skins of citrus fruit (candied peel), Angelica, and ginger. Also, sugaring can be used in the production of jam and jelly.
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 agent. Common chemically pickled food includes 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 lactobacillus’s. Fermented pickles include sauerkraut, nukazuke, kimchi and surströmming.
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.
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 wasn’t understood until 1864 when Louis Pasteur found the relationship between micro-organisms, food spoilage, and illness. Foods have varying degrees of natural protection against spoilage and may require that the final step occur in a pressure cooker. High-acid fruits like strawberries require no preservatives to can and only a short boiling cycle, whereas marginal vegetables such as carrots require longer boiling and addition of other acidic elements. Low-acid foods such as vegetables and meats, require pressure canning. Food preserved by canning or bottling is at intermediate risk of spoilage once the can or bottle has been opened.
Lack of quality control in the canning process may allow ingress of water or micro-organisms. Most such failures are rapidly detected as decomposition within the can causes gas production and the can will swell or burst. However, there have been examples of poor manufacture (under processing) and poor hygiene allowing contamination of canned food by the obligate anaerobe Clostridium botulinum, which produces an acute toxin within the food, leading to severe illness or death. This organism produces no gas or obvious taste and remains undetected by taste or smell. Its toxin is denatured by cooking, however. Cooked mushrooms, handled poorly and the canned, can support the growth of Staphylococcus aureus, which produces a toxin this is not destroyed by canning or subsequent reheating.
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 foods naturally form a protein gel when cooked such as eels and elvers, and sipunculid worms, which are a delicacy in Xiamen, in the Fujian Province of the Republic of China. Jellied eels are a delicacy in the East End of London, where they are eaten with mashed Potatoes, Potted meats in aspic (a gel made from gelatin and clarified meat broth) were a common way of serving meat off-cuts in the UK until 1950s. Many jugged meats are also jellied.
A traditional British way of preserving meat (particularly shrimp) is by setting it in a pot and sealing it with a layer of fat. Also common is potted chicken liver; jellying is one of the steps in producing traditional pates
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 judged is usually cut into pieces, placed into a tightly-sealed jug with brine or gravy, and stewed. Red wine and /or the cooking liquid. Jugging was a popular method of preserving meat up until the middle of the 20th century.
Burial of food can preserve it due to a variety of factors: lack of light, 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. 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. 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 causes 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. Before burial, meat (pig/boar) can be fatted. The tallow of the animal is heated and poured over meat in a barrel. Once the fat hardens the barrel is sealed and buried in a cold cellar or ground
In Orissa, 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
Some foods, such as many cheeses, wines, and beers, use specific micro-organisms that combat spoilage from other less-benign organisms. These micro-organisms keep pathogens in check by creating an environment toxic for themselves and other micro-organisms by producing acid or alcohol. Methods of fermentation include, but are not limited to, starter micro-organisms, salts, hops, controlled (usually cool) temperatures and controlled (usually low) level 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. For example, drinking water in the Middle Ages was dangerous that could spread disease. When the water is made of beer, the boiling during the brewing process kills any bacteria in the water that could made people sick. Additionally, the water now has the nutrients from the barley and other ingredients, and the microorganisms can also produce vitamins as they ferment.