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| '''Food preservation''' is the process of treating and handling ] to stop or greatly slow down spoilage (loss of quality, edibility or nutritive value) caused or accelerated by micro-organisms. Some methods, however, use benign bacteria, yeasts or fungi to add specific qualities and to preserve food (e.g., cheese, wine). While maintaining or creating ]al value, texture and ] is important in preserving its value as food; this is a culturally dependent. What qualifies as food fit for humans in one culture may not qualify in another culture. | |||
| Preservation usually involves preventing the growth of ], ], and other ], as well as retarding the ] of ]s which cause ]. It also includes processes to inhibit natural ageing and discolouration that can occur during food preparation such as the ] reaction in apples which causes browning when apples are cut. Some preservation methods require the food to be sealed after treatment to prevent recontamination with microbes; others, such as drying, allow food to be stored without any special containment for long periods. | |||
| Common methods of applying these processes include ], ], ], ],], ], preserving in syrup, sugar crystallisation, ], and adding ]s or inert ]es such as carbon dioxide. Other methods that not only help to preserve food, but also add flavour, include ], ], ], preserving in ] or ], ] crystallisation and curing. | |||
| == Preservation processes == | |||
| {| width="350" border="1" cellpadding="3" cellspacing="0" align="right" style="margin: 0em 0em 1em 1em;" | |||
| ! Method | |||
| ! Effect on microbial growth or survival | |||
| |- | |||
| | ] | |||
| | Low temperature to retard growth | |||
| |- | |||
| | ] | |||
| | Low temperature and reduction of water activity to prevent microbial growth, slowing of oxidation reactions | |||
| |- | |||
| | ], ] and conserving | |||
| | Reduction in ] sufficient to delay or prevent microbial growth | |||
| |- | |||
| | ] and ] free ] packaging | |||
| | Low ] tension inhibits strict ]s and delays growth of facultative ]s | |||
| |- | |||
| | Carbon dioxide enriched modified atmosphere packaging | |||
| | Specific inhibition of some micro-organisms | |||
| |- | |||
| | Addition of ]s; e.g. ] | |||
| | Reduction of the intracellular ] of micro-organisms | |||
| |- | |||
| | ] ] | |||
| | Reduction of pH value ''in situ'' by microbial action and sometimes additional inhibition by the lactic and ]s formed and by other microbial products. (e.g. ethanol, ]s) | |||
| |- | |||
| | ] preservation | |||
| | Cooking in high sucrose concentration creating too high osmotic pressure for most microbial survival. | |||
| |- | |||
| | ] preservation | |||
| | Steeping or cooking in ] produces toxic inhibition of microbes. Can be combined with sugar preservation | |||
| |- | |||
| | ] | |||
| | Compartmentalisation and ] within the ] droplets in water-in-oil emulsion foods | |||
| |- | |||
| | Addition of preservatives such as ] or ] ions | |||
| | Inhibition of specific groups of micro-organisms | |||
| |- | |||
| | ] and ] | |||
| | Delivery of ] sufficient to inactivate target micro-organisms to the desired extent | |||
| |- | |||
| | ] (], ] and ]) | |||
| | Delivery of ] to disrupt cellular RNA | |||
| |- | |||
| | Application of high hydrostatic pressure (Pascalization) | |||
| | Pressure-inactivation of vegetative bacteria, yeasts and moulds | |||
| |- | |||
| | ] (PEF treatment) | |||
| | Short bursts of electricity for microbial inactivation | |||
| |} | |||
| Preservation processes include: | |||
| * Heating to kill or denature organisms (e.g. boiling) | |||
| * Oxidation (e.g. use of sulphur dioxide) | |||
| * Toxic inhibition (e.g. smoking, use of carbon dioxide, vinegar, alcohol etc) | |||
| * Dehydration (drying) | |||
| * Osmotic inhibition ( e.g. use of syrups) | |||
| * Low temperature inactivation (e.g. freezing) | |||
| * Ultra high water pressure (e.g. fresherized, a kind of “cold” pasteurization, the pressure kills naturally occurring pathogens, which cause food deterioration and affect ].) | |||
| * Many combinations of these methods | |||
| * ] | |||
| == Drying == | |||
| {{Main|Drying (food)}} | |||
| One of the oldest methods of food preservation is by drying, which reduces ] sufficiently to prevent or delay ] growth.{{Fact|date=May 2008}} Drying also reduces weight, making food more portable. Most types of meat can be dried; a good example is beef ]. Many fruits can also be dried; for example, the process is often applied to apples, pears, bananas, mangoes, papaya, apricot, and coconut. ]s, ] and ]s are all forms of dried grapes. Drying is also the normal means of preservation for cereal grains such as wheat, maize, oats, barley, rice, millet and rye. | |||
| == Freezing == | |||
| {{Main|Frozen food}} | |||
| Freezing is also one of the most commonly used processes commercially and domestically for preserving a very wide range of food including prepared food stuffs which 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. | |||
| == Vacuum packing == | |||
| {{Main|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, slowing spoiling. Vacuum-packing is commonly used for storing ] to reduce loss of flavor from oxidation. | |||
| == Salt == | |||
| {{Main|Curing (food preservation)}} | |||
| Salting or curing draws moisture from the meat through a process of osmosis. Meat is ] with salt or sugar, or a combination of the two. Nitrates and nitrites are also often used to cure meat and contribute the characteristic pink color, as well as inhibition of ]. | |||
| == Smoking == | |||
| {{Main|Smoking (food)}} | |||
| - | |||
| Meat, fish and some other foods may be both preserved and flavored through the use of smoke, typically in a ]. The combination of heat to dry the food without cooking it, and the addition of the aromatic (phenolic)hydrocarbons from the smoke preserves the food. | |||
| == Sugar == | |||
| Sugar is used to preserve fruits, either in syrup with fruit such as ]s, ]s, ]es, ]s, ]s or in crystallized form where the preserved material is cooked in sugar to the point of crystallisation and the resultant product is then stored dry. This method is used for the skins of ] fruit (candied peel), ] and ]. A modification of this process produces ] such as glacé ] where the fruit is preserved in sugar but is then extracted from the syrup and sold, the preservation being maintained by the sugar content of the fruit and the superficial coating of syrup. The use of sugar is often combined with alcohol for preservation of luxury products such as fruit in ] or other spirits. These should not be confused with fruit flavored spirits such as ] or ]. | |||
| == Pickling == | |||
| {{Main|Pickling}} | |||
| Pickling is a method of preserving food in an edible ] liquid. Pickling can be broadly categorized as chemical pickling (for example, ]) and ] pickling (for example, making ]). | |||
| In chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other micro-organisms. Typical pickling agents include ] (high in ]), ], ], and ], especially ] but also many other oils. 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 ], ]s, ], ], and ], as well mixed vegetables such as ], ], ], and ]. | |||
| In fermentation pickling, the food itself produces the preservation agent, typically by a process that produces ]. Fermented pickles include ], ], ], ], and ]. Some chemically ]s are also fermented. | |||
| In commercial pickles, a preservative like ] or ] may also be added to enhance ]. | |||
| == 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. Masa harina and ] use lye in their preparation, but not for preservation. | |||
| == Canning and bottling == | |||
| ] | |||
| {{Main|Canning}} | |||
| :''See also ]'' | |||
| ] involves cooking food, sealing it in sterile cans or jars, and ] the containers to kill or weaken any remaining bacteria as a form of ]. Various 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 fruits such as ]es 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, though. Cooked mushrooms, handled poorly and then canned, can support the growth of ], which produces a toxin that is not destroyed by canning or subsequent reheating. | |||
| == Jellying == | |||
| {{Main|Aspic}} | |||
| {{also|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 the town of ] in Fujian province of the ]. ] are a delicacy in the East End of ] where they are eaten with mashed potatoes. Potted meats in ], (a gel made from gelatine and clarified meat broth) were a common way of serving meat off-cuts in the UK until the 1950s. Many jugged meats are also jellied. | |||
| Fruit preserved by jellying is known as ], ], or ]. In this case, the jellying agent is usually ], either added during cooking or arising naturally from the fruit. Most preserved fruit is also sugared. Heating, packaging and acid and sugar provide the preservation. | |||
| == Potting == | |||
| {{see|Potted meat}} | |||
| {{also|Potted shrimps}} | |||
| 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; compare ]. | |||
| == Jugging == | |||
| {{Main|Jugging}} | |||
| Meat can be preserved by jugging, 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. | |||
| == Irradiation == | |||
| {{Main|Food irradiation}} | |||
| Irradiation of food<ref>anon., Food Irradation - A technique for preserving and improving the safety of food, WHO, Geneva, 1991</ref> is the exposure of food to ]; either high-energy ]s or ]s from accelerators, or by ]s (emitted from radioactive sources as ]-60 or ]-137). The treatment has a range of effects, including killing bacteria, molds and insect pests, reducing the ripening and spoiling of fruits, and at higher doses inducing sterility. The technology may be compared to pasteurization; it is sometimes called 'cold pasteurization', as the product is not heated. Irradiation is not effective against viruses or ]s, it cannot eliminate toxins already formed by microorganisms, and is only useful for food of high initial quality. | |||
| The radiation process is unrelated to ], but it may use the radiation emitted from radioactive nuclides produced in nuclear reactors. Ionizing radiation is hazardous to life; for this reason irradiation facilities have a heavily shielded irradiation room where the process takes place. Radiation safety procedures ensure that neither the workers in such facility nor the environment receive any radiation dose from the facility. Irradiated food does not become radioactive, and national and international expert bodies have declared food irradiation as wholesome. However, the wholesomeness of consuming such food is disputed by opponents<ref>Hauther,W. & Worth, M., Zapped! Irradiation and the Death of Food, Food & Water Watch Press, Washington, DC, 2008</ref> and consumer organizations.<ref></ref> National and international expert bodies have declared food irradiation as 'wholesome'; UN-organizations as WHO and FAO are endorsing to use food irradiation. International legislation on whether food may be irradiated or not varies worldwide from no regulation to full banning.<ref></ref> | |||
| It is estimated that about 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<ref></ref><ref>C.M. Deeley, M. Gao, R. Hunter, D.A.E. Ehlermann, The development of food irradiation in the Asia Pacific, the Americas and Europe; tutorial presented to the International Meeting on Radiation Processing, Kuala Lumpur, 2006. http://www.doubleia.org/index.php?sectionid=43&parentid=13&contentid=494</ref>. | |||
| ==Modified atmosphere== | |||
| {{Main|Modified atmosphere}} | |||
| is a way to preserve food by operating on the atmosphere around it. Salad crops which are notoriously difficult to preserve are now being packaged in sealed bags with an atmosphere modified to reduce the oxygen (O<sub>2</sub>) concentration and increase the ] (CO<sub>2</sub>) 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. | |||
| - | |||
| - Grains may be preserved using carbon dioxide. A block of ] is placed in the bottom and the can is filled with grain. The can is then "burped" of excess gas. The ] from the sublimation of the dry ice prevents insects, ], and ] from damaging the grain. Grain stored in this way can remain edible for five years. | |||
| - | |||
| ] gas (N<sub>2</sub>) at concentrations of 98% or higher is also used effectively to kill insects in grain through ]. However, carbon dioxide has an advantage in this respect as it kills organisms through both hypoxia and hypercarbia, requiring concentrations of only 80%, or so. This makes carbon dioxide preferable for fumigation in situations where an ] cannot be maintained. | |||
| == Burial in the ground == | |||
| 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. | |||
| Many root vegetables are very resistant to spoilage and require no other preservation other than storage in cool dark conditions, for example by burial in the ground, such as in a ]. | |||
| ]s are 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. | |||
| Most foods can be preserved in soil that is very dry and salty (thus a ]), or soil that is frozen. | |||
| ] was traditionally buried in the fall in northern farms in the USA for preservation. Some methods keep it crispy while other methods produce ]{{Fact|date=January 2008}}. A similar process is used in the traditional production of ]. | |||
| Sometimes meat is buried under conditions which 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. | |||
| == Controlled use of micro-organism== | |||
| {{see also|Fermentation (food)}} | |||
| Some foods, such as many ]s, ]s, and ]s will keep for a long time because their production uses 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. Starter micro-organisms, salt, hops, controlled (usually cool) temperatures, controlled (usually low) levels of oxygen and/or other methods are used to create the specific controlled conditions that will support the desirable organisms that produce food fit for human consumption. | |||
| ==High pressure food preservation== | |||
| {{main|High pressure food preservation}} | |||
| High pressure food preservation refers to ] used for food preservation. "Pressed inside a vessel exerting 70,000 pounds per square inch or more, food can be processed so that it retains its fresh appearance, flavour, texture and nutrients while disabling harmful microorganisms and slowing spoilage." By 2001, adequate commercial equipment was developed so that by 2005 the process was being used for products ranging from ] to ] to ]s and widely sold.<ref name=military>{{cite news |first= |last= |authorlink= |coauthors= |title=High-Pressure Processing Keeps Food Safe |url=http://web.archive.org/web/20080202232043/http://www.military.com/soldiertech/0,14632,Soldiertech_Squeeze,,00.html |quote=Pressed inside a vessel exerting 70,000 pounds per square inch or more, food can be processed so that it retains its fresh appearance, flavor, texture and nutrients while disabling harmful microorganisms and slowing spoilage. |work=] |date= |accessdate=2008-12-16 }}</ref> | |||
| == See also == | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| == Notes == | |||
| {{reflist}} | |||
| == References == | |||
| {{refbegin}} | |||
| * {{ cite book | title = Food Conservation | first = Astri | last = Riddervold | isbn = 9780907325406 }} | |||
| * {{ cite book | title = Eating for Victory: Food Rationing and the Politics of Domesticity | first = Amy | last = Bentley | isbn = 9780252067273 }} | |||
| * {{ cite book | title = Pickled, Potted, and Canned: How the Art and Science of Food Preserving Changed the World | first = Sue | last = Shephard | isbn = 9780743255530 }} | |||
| {{refend}} | |||
| == External links == | |||
| {{commonscat|Food preservation}} | |||
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