Food preservation

Food preservation prevents the growth of s (such as s), or other microorganisms (although some methods work by introducing benign or fungi to the food), as well as slowing the  of s that cause. Food preservation may also include processes that inhibit visual deterioration, such as the reaction in apples after they are cut during food preparation.

Many processes designed to preserve food involve more than one food preservation method. Preserving fruit by turning it into jam, for example, involves boiling (to 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 and, when compared to modern methods.

Some methods of food preservation are known to create s. In 2015, the of the  classified processed meat, i.e. meat that has undergone salting, curing, fermenting, and smoking, as " to humans".

Maintaining or creating nutritional value, and  is an important aspect of food preservation.

Traditional techniques
New techniques of food preservation became available to the home chef from the dawn of until the.

Curing
The earliest form of curing was dehydration or, used as early as 12,000 BC. and 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 s, and. Salt accelerates the drying process using and also inhibits the growth of several common strains of bacteria. More recently s have been used to cure meat, contributing a characteristic pink colour.

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 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 s and es. Rural people often did their own, whereas town and city dwellers often relied on the. Today, root cellaring remains popular among people who value various goals, including, , traditional home , ing, , , , 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
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
Heating to temperatures which are sufficient to kill microorganisms inside the food is a method used with s. Milk is also boiled before storing to kill many microorganisms.

Sugaring
The earliest cultures have used as a, and it was commonplace to store  in. Similar to pickled foods, was brought to Europe through the trade routes. In northern climates without sufficient sun to dry foods, are made by heating the fruit with sugar. "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 syrup with fruit such as s, s, es, s, and s, 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 fruit (candied peel),, and. Also, sugaring can be used in the production of and.

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 (high in salt),, , and. 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, , , , and , as well as mixed vegetables such as.

In fermentation pickling, bacteria in the liquid produce s as preservation agents, typically by a process that produces through the presence of. Fermented pickles include, , , and.

Lye
makes food too for bacterial growth. Lye will fats in the food, which will change its flavor and texture. uses lye in its preparation, as do some olive recipes. Modern recipes for s also call for lye.

Canning
involves cooking food, sealing it in sterilized cans or jars, and the containers to kill or weaken any remaining bacteria as a form of. It was invented by the French confectioner. 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 found the relationship between microorganisms, food spoilage, and illness.

Foods have varying degrees of natural protection against spoilage and may require that the final step occur in a. High-acid fruits like require no preservatives to can and only a short boiling cycle, whereas marginal vegetables such as s 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 immediate 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 (underprocessing) and poor allowing contamination of canned food by the obligate  , 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 s, handled poorly and then canned, can support the growth of , which produces a toxin that is not destroyed by canning or subsequent reheating.

Jellying
Secondary article: Fruit Preserves Food may be preserved by cooking in a material that solidifies to form a gel. Such materials include, , flour, and  flour. Some foods naturally form a gel when cooked, such as, and  worms, which are a delicacy in , in the Fujian province of the. s are a delicacy in the East End of, where they are eaten with mashed potatoes. Potted meats in (a gel made from gelatin and clarified meat broth) were a common way of serving meat off-cuts in the UK until the 1950s. Many meats are also jellied. A traditional British way of preserving meat (particularly ) 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 s.

Besides jellying of meat and seafood, a widely known type of Jellying is fruit preserves which are preparations of 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, in plural form, "preserves" is used to describe all types of jams and jellies.

Jugging
Meat can be preserved by jugging. Jugging is the process of the meat (commonly  or ) in a covered  jug or. The animal to be jugged is usually cut into pieces, placed into a tightly-sealed jug with brine or, and stewed. 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.

Burial
Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool temperatures, pH level, or s 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 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. s 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. was traditionally buried during in northern US farms for preservation. Some methods keep it crispy while other methods produce. A similar process is used in the traditional production of. 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.

In, 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 in Irish  for centuries.

Confit
Meat can be preserved by salting it, cooking it at or near 100 °C in some kind of (such as  or ), and then storing it immersed in the fat. These preparations were popular in Europe before refrigerators became ubiquitous. They are still popular in, where they are called . The preparation will keep longer if stored in a cold cellar or buried in cold ground.

Fermentation
Some foods, such as many s, s, and s, 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, 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. For example, drinking water in the Middle Ages was dangerous because it often contained pathogens that could spread disease. When the water is made into beer, the boiling during the brewing process kills any bacteria in the water that could make 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.

Modern industrial techniques
Techniques of food preservation were developed in research laboratories for commercial applications.

Pasteurization
Pasteurization is a process for preservation of liquid food. It was originally applied to combat the souring of young local wines. Today, the process is mainly applied to dairy products. In this method, milk is heated at about 70 C for 15–30 seconds to kill the bacteria present in it and cooling it quickly to 10 C to prevent the remaining bacteria from growing. The milk is then stored in sterilized bottles or pouches in cold places. This method was invented by, a chemist, in 1862.

Vacuum packing
Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The environment strips bacteria of oxygen needed for survival. Vacuum-packing is commonly used for storing to reduce loss of flavor from oxidization. A major drawback to vacuum packaging, at the consumer level, is that vacuum sealing can deform contents and rob certain foods, such as cheese, of its flavor.

Artificial food additives
Preservative food additives can be antimicrobial—which inhibit the growth of or, including —or , such as s, which inhibit the  of food constituents. Common antimicrobial preservatives include, , , s (, , , etc.), and. s include (BHA) and  (BHT). Other preservatives include (usually in solution),  (insecticide),, and.

Irradiation
Irradiation of food is the exposure of food to. Multiple types of ionizing radiation can be used, including s (high-energy s) and s (emitted from radioactive sources such as or ). Irradiation can kill bacteria, molds, and insect pests, reduce the ripening and spoiling of fruits, and at higher doses induce sterility. The technology may be compared to ; it is sometimes called "cold pasteurization", as the product is not heated. Irradiation may allow lower-quality or contaminated foods to be rendered marketable.

National and international expert bodies have declared food irradiation as "wholesome"; organizations of the, such as the and , endorse food irradiation. Consumers may have a negative view of irradiated food based on the misconception that such food is radioactive; in fact, irradiated food does not and cannot become radioactive. Activists have also opposed food irradiation for other reasons, for example, arguing that irradiation can be used to sterilize contaminated food without resolving the underlying cause of the contamination. International legislation on whether food may be irradiated or not varies worldwide from no regulation to a full ban.

Approximately 500,000 tons of food items are irradiated per year worldwide in over 40 countries. These are mainly s and s, with an increasing segment of fresh fruit irradiated for fruit fly quarantine.

Pulsed electric field electroporation
Pulsed electric field (PEF) electroporation is a method for processing cells by means of brief pulses of a strong electric field. PEF holds potential as a type of low-temperature alternative pasteurization process for sterilizing food products. In PEF processing, a substance is placed between two electrodes, then the pulsed electric field is applied. The electric field enlarges the pores of the cell membranes, which kills the cells and releases their contents. PEF for food processing is a developing technology still being researched. There have been limited industrial applications of PEF processing for the pasteurization of fruit juices. To date, several PEF treated juices are available on the market in Europe. Furthermore, for several years a juice pasteurization application in the US has used PEF. For cell disintegration purposes especially potato processors show great interest in PEF technology as an efficient alternative for their preheaters. Potato applications are already operational in the US and Canada. There are also commercial PEF potato applications in various countries in Europe, as well as in Australia, India, and China.

Modified atmosphere
Modifying atmosphere is a way to preserve food by operating on the atmosphere around it. Salad crops that are notoriously difficult to preserve are now being packaged in sealed bags with an atmosphere modified to reduce the oxygen (O2) concentration and increase the (CO2) concentration. There is concern that, although salad vegetables retain their appearance and texture in such conditions, this method of preservation may not retain nutrients, especially s. There are two methods for preserving grains with carbon dioxide. One method is placing a block of in the bottom and filling the can with the grain. Another method is purging the container from the bottom by gaseous carbon dioxide from a cylinder or bulk supply vessel.

prevents insects and, depending on concentration, and  from damaging the grain. Grain stored in this way can remain edible for approximately five years.

gas (N2) at concentrations of 98% or higher is also used effectively to kill insects in the grain through. However, carbon dioxide has an advantage in this respect, as it kills organisms through and hypoxia (depending on concentration), but it requires concentrations of above 35%, or so. This makes carbon dioxide preferable for fumigation in situations where a cannot be maintained.

Controlled Atmospheric Storage (CA): "CA storage is a non-chemical process. Oxygen levels in the sealed rooms are reduced, usually by the infusion of nitrogen gas, from the approximate 21 percent in the air we breathe to 1 percent or 2 percent. Temperatures are kept at a constant 0–2 C. Humidity is maintained at 95 percent and carbon dioxide levels are also controlled. Exact conditions in the rooms are set according to the apple variety. Researchers develop specific regimens for each variety to achieve the best quality. Computers help keep conditions constant." "Eastern Washington, where most of Washington’s apples are grown, has enough warehouse storage for 181 million boxes of fruit, according to a report done in 1997 by managers for the Washington State Department of Agriculture Plant Services Division. The storage capacity study shows that 67 percent of that space—enough for 121,008,000 boxes of apples—is CA storage."

Air-tight storage of grains (sometimes called hermetic storage) relies on the respiration of grain, insects, and fungi that can modify the enclosed atmosphere sufficiently to control insect pests. This is a method of great antiquity, as well as having modern equivalents. The success of the method relies on having the correct mix of sealing, grain moisture, and temperature.

A patented process uses s to exhaust and automatically maintain the exhaustion of in a shipping container, containing, for example, fresh fish.

Nonthermal plasma
This process subjects the surface of food to a "flame" of ionized gas molecules, such as helium or nitrogen. This causes micro-organisms to die off on the surface.

High-pressure food preservation
High-pressure food preservation or pascalization refers to the use of a food preservation technique that makes use of. "Pressed inside a vessel exerting 70,000 psi or more, food can be processed so that it retains its fresh appearance, flavor, texture and nutrients while disabling harmful microorganisms and slowing spoilage." By 2005, the process was being used for products ranging from to  to s and widely sold.

Biopreservation
is the use of natural or controlled or s as a way of preserving food and extending its. Beneficial bacteria or the products produced by these bacteria are used in biopreservation to control spoilage and render s inactive in food. It is a benign ecological approach which is gaining increasing attention.

Of special interest are (LAB). Lactic acid bacteria have antagonistic properties that make them particularly useful as biopreservatives. When LABs compete for nutrients, their s often include active antimicrobials such as lactic acid, acetic acid, hydrogen peroxide, and s. Some LABs produce the antimicrobial, which is a particularly effective preservative.

These days, LAB bacteriocins are used as an integral part of. Using them in combination with other preservative techniques can effectively control spoilage bacteria and other pathogens, and can inhibit the activities of a wide spectrum of organisms, including inherently resistant.

Hurdle technology
is a method of ensuring that s in s can be eliminated or controlled by combining more than one approach. These approaches can be thought of as "hurdles" the pathogen has to overcome if it is to remain active in the food. The right combination of hurdles can ensure all pathogens are eliminated or rendered harmless in the final product.

Hurdle technology has been defined by Leistner (2000) as an intelligent combination of hurdles that secures the safety and stability as well as the  and nutritional quality and the economic viability of s. The organoleptic quality of the food refers to its sensory properties, that is its look, taste, smell, and texture.

Examples of hurdles in a food system are high temperature during processing, low temperature during storage, increasing the, lowering the or , and the presence of s or s. According to the type of pathogens and how risky they are, the intensity of the hurdles can be adjusted individually to meet consumer preferences in an economical way, without sacrificing the safety of the product.