View source for Food preservation

{{Short description|Inhibition of microbial growth in food}}
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{{Use dmy dates|date=June 2020}}
[[File:Food lab scientist packages food for spaceflight at Space Food Lab.jpg|thumb|upright=1.5|alt=Man holding a small pastry inside plastic wrappings|A [[food scientist]] is preparing a meal for [[astronaut]]s in space.]]
'''Food preservation''' includes processes that make [[food]] more resistant to [[microorganism]] growth and slow the [[redox|oxidation]] of [[fat]]s. This slows down the [[decomposition]] and [[rancidification]] process. 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. By preserving [[food]], [[food waste]] can be reduced, which is an important way to decrease production costs and increase the efficiency of [[food system]]s, improve [[food security]] and [[nutrition]] and contribute towards [[environmental sustainability]].<ref>{{Cite book|url=http://www.fao.org/documents/card/en/c/ca6122en|title=The State of Food and Agriculture 2019. Moving forward on food loss and waste reduction, In brief|publisher=FAO|year=2021|location=Rome|pages=8|doi=10.4060/ca9825fr |isbn=978-92-5-134306-7 }}</ref> For instance, it can reduce the [[Environmental impact of agriculture|environmental impact of food production]].<ref name="Sust">{{Cite web|date=2016-03-11|title=Good food for a better future|url=https://www.sdgfund.org/good-food-better-future|access-date=2020-11-03|website=Sustainable Development Goals Fund|language=en}}</ref>

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).

Different food preservation methods have different impacts on the quality of the food and food systems. Some traditional methods of preserving food have been shown to have a lower [[Waste hierarchy|energy input]] and [[carbon footprint]] compared to modern methods.<ref>{{Cite book|title=Fields of Farmers by Joel Salatin {{!}} Chelsea Green Publishing|url=https://www.chelseagreen.com/product/fields-of-farmers/|access-date=2020-11-03|language=en-US}}</ref><ref name="Sust" /> Some methods of food preservation are also known to create [[carcinogen]]s.

== Traditional techniques ==
Some techniques of food preservation pre-date the [[Neolithic Revolution|dawn of agriculture]]. Others were discovered more recently.

=== Boiling ===
{{Main|Boiling}}
{{See also|Pasteurisation}}
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 [[desiccant]]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 [[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 egg]]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.

=== Canning ===
[[File:PreservedFood1.jpg|thumb|right|Preserved food]]
{{Main|Canning}}
{{See also|Home 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 (microbiology)|sterilization]]. It was invented by the French confectioner [[Nicolas Appert]].<ref>''Nicolas Appert inventeur et humaniste'' by Jean-Paul Barbier, Paris, 1994 and http://www.appert-aina.com {{Webarchive|url=https://web.archive.org/web/20110904053635/http://www.appert-aina.com/ |date=4 September 2011 }}</ref> 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.<ref name="nchfp.uga.edu" />

Foods have varying degrees of natural protection against spoilage and may require that the final step occurs in a [[pressure cooker]]. High-acid fruits like [[Strawberry|strawberries]] require no preservatives to can and only a short boiling cycle, whereas marginal vegetables such as [[carrot]]s require longer boiling and the 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 cause gas production and the can will swell or burst. However, there have been examples of poor manufacture (underprocessing) and poor [[hygiene]] allowing contamination of canned food by the obligate [[Anaerobic organism|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 [[mushroom]]s, when handled poorly and then canned, can support the growth of ''[[Staphylococcus aureus]]'', which produces a toxin that is not destroyed by canning or subsequent reheating.

=== Confit ===
{{Main|Confit}}
Meat can be preserved by salting it, cooking it at or near {{cvt|100|C}} in some kind of fat (such as [[lard]] or [[tallow]]), and then storing it immersed in the fat. These preparations were popular in Europe before refrigerators became ubiquitous.  They are still popular in France, where the term originates.<ref name=aidells>Bruce Aidells (2012): ''[https://books.google.com/books?id=YN4t61JFQe4C&pg=PA429 The Great Meat Cookbook]'', page 429. Houghton Mifflin Harcourt; 632 pages. {{ISBN|9780547241418}}</ref><ref name=jung>Susan Jung (2012): "[https://www.scmp.com/magazines/post-magazine/article/1073828/truc-confit-fat-fabulous-way-preserve-meat Truc: confit, a fat-fabulous way to preserve meat]". ''Post Magazine'', online article, posted on 2012-11-03, accessed 2019-02-21.</ref> The preparation will keep longer if stored in a cold cellar or buried in cold ground.

=== Cooling ===
{{Main|Refrigeration}}
[[Refrigeration|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 cellar]]s and [[icebox]]es. 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 plant|heirloom crops]], traditional home [[list of cooking techniques|cooking techniques]], [[family farm]]ing, [[frugality]], [[self-sufficiency]], [[organic farming]], and others.

=== Curing ===
[[File:Prague powder No 1.jpg|thumb|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.]]
{{Main|Curing (food preservation)}}
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 [[osmotic concentration|solute concentration]] in the food and hence decreases its [[water potential]], the food becomes inhospitable for the [[Microorganism|microbial]] growth that causes [[food spoilage]]. [[Smoking (cooking)|Smoking]] and [[salting (food)|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 [[phenol]]s [[syringol]], [[guaiacol]] and [[catechol]].<ref name="Msagati, T. 2012">Msagati, T. (2012). "The Chemistry of Food Additives and Preservatives"</ref> Salt accelerates the drying process using [[osmosis]] and also inhibits the growth of several common strains of bacteria. More recently [[nitrite]]s have been used to cure meat, contributing a characteristic pink colour.<ref>{{cite web|last1=Nummer|first1=Brian|last2=Andress|first2=Elizabeth|title=Curing and Smoking Meats for Home Food Preservation|url=http://nchfp.uga.edu/publications/nchfp/lit_rev/cure_smoke_cure.html|publisher=National Center for Home Food Preservation|date=June 2015|access-date=30 May 2017|archive-date=24 January 2018|archive-url=https://web.archive.org/web/20180124073339/http://nchfp.uga.edu/publications/nchfp/lit_rev/cure_smoke_cure.html|url-status=dead}}</ref>

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".<ref>{{cite web |url= http://www.cancer.org/cancer/news/news/world-health-organization-says-processed-meat-causes-cancer |title= World Health Organization Says Processed Meat Causes Cancer |author= Stacy Simon |work= Cancer.org |date= 26 October 2015 |access-date= 14 January 2016 |archive-date= 7 January 2017 |archive-url= https://web.archive.org/web/20170107043239/http://www.cancer.org/cancer/news/news/world-health-organization-says-processed-meat-causes-cancer |url-status= dead }}</ref><ref>{{cite news |url=https://www.bbc.co.uk/news/health-34615621 |title = Processed meats do cause cancer – WHO|author= James Gallagher|work= BBC |date=26 October 2015 }}</ref><ref>{{cite web |url=https://www.iarc.fr/en/media-centre/pr/2015/pdfs/pr240_E.pdf| title=IARC Monographs evaluate consumption of red meat and processed meat |work= International Agency for Research on Cancer |date= 26 October 2015}}</ref>

==== Drying ====
[[File:Fish drying in the sun poisson seche Madagascar.jpg|thumb|Flattened [[fish]] drying in the Sun]]
{{Main|Food drying}}
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.<ref name="uog">[http://www.uga.edu/nchfp/publications/nchfp/factsheets/food_pres_hist.html "Historical Origins of Food Preservation".] {{Webarchive|url=https://web.archive.org/web/20111015194629/http://www.uga.edu/nchfp/publications/nchfp/factsheets/food_pres_hist.html |date=15 October 2011 }} Accessed June 2011.</ref> Water is traditionally removed through [[evaporation]] by using methods such as air drying, sun drying, smoking or wind drying, although today electric [[food dehydrator]]s can be used to speed the drying process and ensure more consistent results.<ref>{{cite book |editor1-last=Rahman |editor1-first=M. Shafiur |title=Handbook of Food Preservation |date=2007 |publisher=CRC Press |location=Boca Raton |isbn=9781420017373 |edition=2nd |language=en}}</ref>

=== Fermentation ===
{{Main|Fermentation (food)}}
Some foods, such as many [[cheese]]s, [[wine]]s, and [[beer]]s, are prepared by fermentation. This involves cultivating specific [[Microorganism|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.<ref name="nchfp.uga.edu" /> However, the common belief that premodern people avoided drinking ordinary water is a myth. While people avoided drinking dirty or polluted water, they also avoided using it for the production of beer and wine. Water was visually inspected, smelled, tasted, filtered, and boiled if necessary. It was used for drinking as well as for diluting wine, cooking, and many other processes.<ref>{{Cite web |last=Medievalists.net |date=2023-05-28 |title=Did people drink water in the Middle Ages? |url=https://www.medievalists.net/2023/05/drink-water-middle-ages/ |access-date=2024-08-23 |website=Medievalists.net |language=en-US}}</ref>

=== Freezing ===
{{Main|Frozen food}}
[[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 stew]]s.

=== Jellying ===
{{Main|Aspic}}
{{See also|Fruit preserves|Confit}}
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. [[Eel|Eels and elvers]], and [[Sipuncula|sipunculid]] worms, are a delicacy in [[Xiamen]], China, as are [[jellied eel]]s in the [[East End of London]], where they are eaten with mashed potatoes. [[British cuisine]] has a rich tradition of [[potted meat]]s. 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 [[pâté]]s. Many [[jugging|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 jar]]s. 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; [[jam]]s, [[jelly (fruit preserves)|jellies]], and [[marmalade]]s 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 ===
{{Main|Jugging}}
Meat can be preserved by jugging. Jugging is the process of [[stewing]] the meat (commonly [[game (food)|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'' ===
{{Main|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.<ref>{{Cite web |last=Glinski |first=Stefanie |date=2021-03-25 |title=The Ancient Method That Keeps Afghanistan's Grapes Fresh All Winter |url=http://www.atlasobscura.com/articles/how-did-people-store-fruit-before-fridges |access-date=2023-12-06 |website=Atlas Obscura |language=en}}</ref>

=== Lye ===
{{Main|Sodium hydroxide#Food preparation}}
[[Sodium hydroxide]] ([[lye]]) makes food too [[alkaline]] for bacterial growth. Lye will [[saponification|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 egg]]s also call for lye.

=== Pickling ===
{{Main|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]], [[ethanol|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 [[Pickled cucumber|cucumbers]], [[capsicum|peppers]], [[corned beef]], [[herring]], and [[Pickled egg|eggs]], as well as mixed vegetables such as [[piccalilli]].

In fermentation pickling, bacteria in the liquid produce [[organic acid]]s 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 ===
{{Redirect|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."<ref name="Msagati, T. 2012" /> 

In northern climates without sufficient sun to dry foods, [[preserves]] are made by heating the fruit with sugar.<ref name="nchfp.uga.edu">{{cite web |last1=Nummer |first1=Brian A. |title=National Center for Home Food Preservation {{!}} NCHFP Publications |url=https://nchfp.uga.edu/publications/nchfp/factsheets/food_pres_hist.html |website=National Center for Home Food Preservation |archive-url=https://web.archive.org/web/20140523123409/https://nchfp.uga.edu/publications/nchfp/factsheets/food_pres_hist.html |archive-date=23 May 2014 |language=en}}</ref> 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 ==
Techniques of food preservation were developed in research laboratories for commercial applications.

===Aseptic processing===
{{main|Aseptic processing}}
Aseptic processing works by placing sterilized food (typically by heat, see [[ultra-high temperature processing]]) into sterlized packaging material under sterile conditions. The result is a sealed, sterile food product similar to canned food, but depending on the technique used, damage to food quality is typically reduced compared to canned food. A greater variety of packaging materials can be used as well.

Besides UHT, aseptic processing may be used in conjunction with any of the microbe-reduction technologies listed below. With pasteurization and "high pressure pasteurization", the food may not be completely sterilized (instead achieving a specified [[log reduction]]), but the use of sterile packaging and environments is retained.

=== Pasteurization ===
{{Main|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 {{cvt|70|C|F}} for 15–30 seconds to kill the bacteria present in it and cooling it quickly to {{cvt|10|C|F}} 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 [[Louis Pasteur]], a [[French people|French]] chemist, in 1862.

=== Vacuum packing ===
{{Main|Vacuum packing}}
Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The [[vacuum]] environment strips bacteria of oxygen needed for survival. Vacuum-packing is commonly used for storing [[nut (fruit)|nuts]] 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.

=== Freeze drying ===
{{excerpt|only=paragraphs|Freeze drying}}

=== Preservatives ===
{{Main|Preservatives|Sulfite food and beverage additives}}
Preservative [[food additives]] can be ''[[antimicrobial]]'' – which inhibit the growth of [[bacterium|bacteria]] or [[Fungus|fungi]], including [[Mold (fungus)|mold]] – or ''[[antioxidant]]'', such as [[oxygen absorber]]s, which inhibit the [[oxidation]] of food constituents. Common antimicrobial preservatives include [[nisin]], [[sorbate]]s, [[calcium propionate]], [[sodium nitrate]]/[[sodium nitrite|nitrite]], [[sulfite]]s ([[sulfur dioxide]], [[sodium bisulfite]], [[potassium hydrogen sulfite]], etc.), [[EDTA]], [[hinokitiol]], and [[polylysine|ε-polylysine]]. [[Antioxidant]]s include [[tocopherol]]s (Vitamin E), [[butylated hydroxyanisole]] (BHA) and [[butylated hydroxytoluene]] (BHT). Other preservatives include [[ethanol]].

There is also another approach of impregnating packaging materials (plastic films or other) with antioxidants and antimicrobials.<ref>{{cite journal |last1=Yildirim |first1=Selçuk |last2=Röcker |first2=Bettina |last3=Pettersen |first3=Marit Kvalvåg |last4=Nilsen-Nygaard |first4=Julie |last5=Ayhan |first5=Zehra |last6=Rutkaite |first6=Ramune |last7=Radusin |first7=Tanja |last8=Suminska |first8=Patrycja |last9=Marcos |first9=Begonya |last10=Coma |first10=Véronique |title=Active Packaging Applications for Food: Active packaging applications for food… |journal=Comprehensive Reviews in Food Science and Food Safety |date=January 2018 |volume=17 |issue=1 |pages=165–199 |doi=10.1111/1541-4337.12322|pmid=33350066 |doi-access=free |hdl=20.500.12327/362 |hdl-access=free }}</ref><ref name=Book>{{cite book |last1=L. Brody |first1=Aaron |last2=Strupinsky |first2=E. P. |last3=Kline |first3=Lauri R. |title=Active Packaging for Food Applications |date=2001 |publisher=CRC Press |isbn=9780367397289 |edition=1}}</ref>

=== Irradiation ===
{{Main|Food irradiation}}
Irradiation of food<ref>''Food Irradation – A technique for preserving and improving the safety of food'', WHO, Geneva, 1991</ref> is the exposure of food to [[ionizing radiation]]. Multiple types of ionizing radiation can be used, including [[beta particle]]s (high-energy [[electron]]s) and [[gamma ray]]s (emitted from radioactive sources such as [[cobalt-60]] or [[cesium-137]]). 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 [[pasteurization]]; 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 [[United Nations]], such as the [[World Health Organization]] and [[Food and Agriculture Organization]], endorse food irradiation.<ref name="JECFI">World Health Organization. Wholesomeness of irradiated food. Geneva, Technical Report Series No. 659, 1981</ref><ref name="JSGHDI">World Health Organization. High-Dose Irradiation: Wholesomeness of Food Irradiated With Doses Above 10 kGy. Report of a Joint FAO/IAEA/WHO Study Group. Geneva, Switzerland: World Health Organization; 1999. WHO Technical Report Series No. 890</ref> Consumers may have a negative view of irradiated food based on the misconception that such food is radioactive;<ref>Conley, S.T., What do consumers think about irradiated foods, FSIS Food Safety Review (Fall 1992), 11–15</ref> 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.<ref>Hauter, W. & Worth, M., ''Zapped! Irradiation and the Death of Food'', Food & Water Watch Press, Washington, DC, 2008</ref> International legislation on whether food may be irradiated or not varies worldwide from no regulation to a full ban.<ref>[http://nucleus.iaea.org/NUCLEUS/nucleus/Content/Applications/FICdb/FoodIrradiationClearances.jsp?module=cif NUCLEUS – Food Irradiation Clearances] {{webarchive|url=https://web.archive.org/web/20080526025627/http://nucleus.iaea.org/NUCLEUS/nucleus/Content/Applications/FICdb/FoodIrradiationClearances.jsp?module=cif |date=26 May 2008 }}</ref>

Approximately 500,000 tons of food items are irradiated per year worldwide in over 40 countries. These are mainly [[spice]]s and [[condiment]]s, with an increasing segment of fresh fruit irradiated for fruit fly quarantine.<ref>[http://www.mindfully.org/Food/Irradiation-Position-ADA.htm Food irradiation – Position of ADA J Am Diet Assoc. 2000;100:246-253] {{webarchive|url=https://web.archive.org/web/20160216174601/http://www.mindfully.org/Food/Irradiation-Position-ADA.htm |date=16 February 2016 }}</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. {{usurped|1=[https://web.archive.org/web/20170202002120/http://doubleia.org/index.php?sectionid=43&parentid=13&contentid=494]}}</ref>

=== Pulsed electric field electroporation ===
{{Main|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 ===
{{Main|Modified atmosphere}}

Modifying atmosphere is a way to preserve food by operating on the atmosphere around it. It is often used to package:
* Fresh fruits and vegetables, especially salds crops, which contain living cells that respire even while refrigerated. Reducing oxygen ({{chem2|O2}}) concentration and increasing the [[carbon dioxide]] ({{CO2}}) concentration slows down their respiration, conserves stored energy, and therefore increases shelf life.<ref name="Brody, A.L., Zhuang, H.-2011">{{Cite book|title=Modified atmosphere packaging for fresh-cut fruits and vegetables|last=Brody, A.L., Zhuang, H.|first=Han, J.H|publisher=Blackwell Publishing Ltd|year=2011|isbn=978-0-8138-1274-8|location=West Sussex, UK|pages=57–67}}</ref> High humidity is also used to reduce water loss.<ref>{{Cite web |url=http://www.bestapples.com/facts/facts_controlled.aspx |title=Controlled Atmospheric Storage (CA) :: Washington State Apple Commission |access-date=8 August 2013 |archive-date=14 March 2012 |archive-url=https://web.archive.org/web/20120314160122/http://www.bestapples.com/facts/facts_controlled.aspx |url-status=dead }}</ref>
* Red meat, which needs high {{chem2|O2}} to reduce oxidation of [[myoglobin]] and maintain an attractive bright red color of the meat.<ref name="Djenane, D.-2018">{{Cite journal|last=Djenane, D.|first=Roncales, P.|date=2018|title=Carbon monoxide in meat and fish packaging: advantages and limits|journal=Foods|volume=7|issue=2|pages=12|doi=10.3390/foods7020012|pmid=29360803|pmc=5848116|doi-access=free}}</ref>
* Other meat and fish, which uses higher {{chem2|CO2}} to reduce oxidation and slow down some microbes.<ref name="Fellows, P.J-2017">{{Cite book|title=Food processing technology: principles and practice (4th ed)|last=Fellows, P.J|publisher=Woodhead Publishing|year=2017|isbn=978-0-08-101907-8|location=Duxford, UK|pages=992–1001}}</ref>

=== Nonthermal plasma ===
{{Main|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.<ref>NWT magazine, December 2012</ref>

=== High-pressure food preservation ===
{{Main|Pascalization}}
[[High pressure]] can be used to disable harmful microorganisms and spoilage enzymes while retaining the food's fresh appearance, flavor, texture and nutrients.  By 2005, the process was being used for products ranging from [[orange juice]] to [[guacamole]] to [[deli meat]]s and widely sold.<ref name=military>{{cite news |title=High-Pressure Processing Keeps Food Safe |url=http://www.military.com/soldiertech/0,14632,Soldiertech_Squeeze,,00.html |work=[[Military.com]] |access-date=2008-12-16 |archive-url = https://web.archive.org/web/20080202232043/http://www.military.com/soldiertech/0,14632,Soldiertech_Squeeze,,00.html |archive-date = 2008-02-02}}</ref> Depending on temperature and pressure settings, HP processing can achieve either pasteurization-equivalent [[log reduction]] or go all the way to achieve sterilization of all microbes.<ref>{{cite journal |last1=Aganovic |first1=Kemal |last2=Hertel |first2=Christian |last3=Vogel |first3=Rudi. F. |last4=Johne |first4=Reimar |last5=Schlüter |first5=Oliver |last6=Schwarzenbolz |first6=Uwe |last7=Jäger |first7=Henry |last8=Holzhauser |first8=Thomas |last9=Bergmair |first9=Johannes |last10=Roth |first10=Angelika |last11=Sevenich |first11=Robert |last12=Bandick |first12=Niels |last13=Kulling |first13=Sabine E. |last14=Knorr |first14=Dietrich |last15=Engel |first15=Karl-Heinz |last16=Heinz |first16=Volker |title=Aspects of high hydrostatic pressure food processing: Perspectives on technology and food safety |journal=Comprehensive Reviews in Food Science and Food Safety |date=July 2021 |volume=20 |issue=4 |pages=3225–3266 |doi=10.1111/1541-4337.12763|pmid=34056857 |s2cid=235256047 |url=https://mediatum.ub.tum.de/1624516 }}</ref>

=== Biopreservation ===
[[File:Nisin 1WCO.png|thumb|right|3D stick model of [[nisin]]. Some [[lactic acid bacteria]] manufacture nisin. It is a particularly effective preservative.]]
{{Main|Biopreservation}}

[[Biopreservation]] is the use of natural or controlled [[Microflora|microbiota]] or [[antimicrobial]]s as a way of preserving food and extending its [[shelf life]].<ref name="Ananou1 et al" /> Beneficial bacteria or the [[fermentation (biochemistry)|fermentation]] products produced by these bacteria are used in biopreservation to control spoilage and render [[pathogen]]s inactive in food.<ref name="Yousef&Carlstrom">Yousef AE and Carolyn Carlstrom C (2003) [https://books.google.com/books?id=aYORXplZq0wC&dq=biopreservation&pg=PA226 ''Food microbiology: a laboratory manual''] Wiley, Page 226. {{ISBN|978-0-471-39105-0}}.</ref> It is a benign ecological approach which is gaining increasing attention.<ref name="Ananou1 et al">Ananou S, Maqueda M, Martínez-Bueno M and Valdivia E (2007) [http://www.formatex.org/microbio/pdf/Pages475-486.pdf "Biopreservation, an ecological approach to improve the safety and shelf-life of foods"] {{Webarchive|url=https://web.archive.org/web/20110726061822/http://www.formatex.org/microbio/pdf/Pages475-486.pdf |date=26 July 2011 }} In: A. Méndez-Vilas (Ed.) ''Communicating Current Research and Educational Topics and Trends in Applied Microbiology'', Formatex. {{ISBN|978-84-611-9423-0}}.</ref>

[[Lactic acid bacteria]] (LAB) have antagonistic properties that make them particularly useful as biopreservatives. When LABs compete for nutrients, their [[metabolite]]s often include active antimicrobials such as lactic acid, acetic acid, hydrogen peroxide, and [[peptide]] [[bacteriocin]]s. Some LABs produce the antimicrobial [[nisin]], which is a particularly effective preservative.<ref name="FAO preservation">FAO: [http://www.fao.org/fishery/topic/12322/en Preservation techniques] Fisheries and aquaculture department, Rome. Updated 27 May 2005. Retrieved 14 March 2011.</ref><ref>Alzamora SM, Tapia MS and López-Malo A (2000) [https://books.google.com/books?id=2gTCY5Dvha4C&dq=biopreservation&pg=PA266 ''Minimally processed fruits and vegetables: fundamental aspects and applications''] Springer, p. 266. {{ISBN|978-0-8342-1672-3}}.</ref>

LAB bacteriocins are used in the present day as an integral part of [[hurdle technology]]. 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 [[Gram-negative bacteria]].<ref name="Ananou1 et al" />

=== Hurdle technology ===
{{Main|Hurdle technology}}

[[Hurdle technology]] is a method of ensuring that [[pathogen]]s in [[food product]]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.<ref name="Alasalvar" />

Hurdle technology has been defined by Leistner (2000) as an intelligent combination of hurdles that secures the [[microbial]] safety and stability as well as the [[organoleptic]] and nutritional quality and the economic viability of [[food product]]s.<ref>Leistner I (2000) [http://envismadrasuniv.org/Physiology/pdf/Basic%20aspects%20of%20food%20preservation.pdf "Basic aspects of food preservation by hurdle technology"] ''International Journal of Food Microbiology'', '''55''':181–186.</ref> 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 [[acidity]], lowering the [[water activity]] or [[redox potential]], and the presence of [[preservative]]s or [[biopreservative]]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.<ref name="Alasalvar">Alasalvar C (2010) [https://books.google.com/books?id=l-APOWUVp-8C&pg=PT232&dq=%22hurdle+technology%22|%22hurdle+technologies%22&hl=en&ei=5GSFTaTGCJCSuAOj66zGCA&sa=X&oi=book_result&ct=result&resnum=3&ved=0CDgQ6AEwAg#v=onepage&q=%22hurdle%20technology%22|%22hurdle%20technologies%22&f=false ''Seafood Quality, Safety and Health Applications''] John Wiley and Sons, Page 203. {{ISBN|978-1-4051-8070-2}}.</ref>

{| class="wikitable"
|+ Principal hurdles used for food preservation (after Leistner, 1995)<ref>Leistner L (1995) [https://books.google.com/books?id=6a_dbGRoiWIC&q=Principles+and+applications+of+hurdle+technology "Principles and applications of hurdle technology"] In Gould GW (Ed.) ''New Methods of Food Preservation'', Springer, pp. 1–21. {{ISBN|978-0-8342-1341-8}}.</ref><ref name="Lee">Lee S (2004) [http://www.internetjfs.org/articles/ijfsv4-3.pdf "Microbial Safety of Pickled Fruits and Vegetables and Hurdle Technology"] {{Webarchive|url=https://web.archive.org/web/20110901001910/http://www.internetjfs.org/articles/ijfsv4-3.pdf |date=1 September 2011 }} ''Internet Journal of Food Safety'', '''4''': 21–32.</ref>
|-
! Parameter
! Symbol
! Application
|-
| High temperature
| style="text-align:center;"| F
| Heating
|-
| Low temperature
| style="text-align:center;"| T
| [[Refrigeration|Chilling]], [[Frozen food|freezing]]
|-
| Reduced [[water activity]]
| style="text-align:center;"| a{{sub|w}}
| [[Drying]], [[Curing (food preservation)|curing]], [[Conserve (condiment)|conserving]]
|-
| Increased [[acidity]]
| style="text-align:center;"| [[pH]]
| Acid addition or formation
|-
| Reduced [[redox potential]]
| style="text-align:center;"| E{{sub|h}}
| Removal of oxygen or addition of [[ascorbate]]
|-
| [[Biopreservative]]s
|
| Competitive [[flora]] such as [[microbial]] [[Fermentation (food)|fermentation]]
|-
| Other [[preservative]]s
|
| [[Sorbate]]s, [[sulfite]]s, [[nitrite]]s
|}

== See also ==
{{Portal|Food}}
{{div col|colwidth=25em}}
* [[Blast chilling]]
* [[Food engineering]]
* [[Food microbiology]]
* [[Food packaging]]
* [[Food rheology]]
* [[Food science]]
* [[Food spoilage]]
* [[Freeze-drying]]
* [[Fresherized]]
* [[List of dried foods]]
* [[List of pickled foods]]
* [[List of smoked foods]]
* [[Shelf life]]
{{Div col end}}

== Notes ==
{{Reflist}}

== Sources ==
* {{Free-content attribution
| title = The State of Food and Agriculture 2019. Moving forward on food loss and waste reduction, In brief
| author = FAO
| publisher = FAO
| page numbers = 24
| source =
| documentURL =http://www.fao.org/documents/card/en/c/ca6122en
| license statement URL = https://commons.wikimedia.org/wiki/File:The_State_of_Food_and_Agriculture_2019._Moving_forward_on_food_loss_and_waste_reduction,_In_brief.pdf
| license = CC BY-SA 3.0
}}

== References ==
{{Refbegin}}
* {{cite book | title = Food Conservation | first = Astri | last = Riddervold | year = 1988 | publisher = Prospect | isbn = 978-0-907325-40-6}}
* {{cite news | title = Thermal food processing optimization: algorithms and software | first = Nunes | last = Abakarov | journal = Food Engineering | url = http://tomakechoice.com/paper/OPTPROx.pdf | access-date = 22 October 2012 | archive-date = 21 February 2014 | archive-url = https://web.archive.org/web/20140221161833/http://tomakechoice.com/paper/OPTPROx.pdf | url-status = dead }}
* {{cite news | title = Multi-criteria optimization and decision-making approach for improving of food engineering processes | first = Sushkov, Mascheroni | last = Abakarov | journal = International Journal of Food Studies | url = http://tomakechoice.com/paper/MCDM&OD_IJFS.pdf | access-date = 9 June 2021 | archive-date = 21 December 2018 | archive-url = https://web.archive.org/web/20181221185608/http://tomakechoice.com/paper/MCDM%26OD_IJFS.pdf | url-status = dead }}
{{Refend}}

==Further reading==
* {{Cite book |last=Marx de Salcedo |first=Anastacia |year=2015 |title=Combat-ready Kitchen: How the U.S. military shapes the way you eat |location=New York |publisher=Current/Penguin |isbn=9781101601648 }}

== External links ==
{{Commons category|Food preservation}}
* [http://home.datacomm.ch/kerguelen/gustav_hammer A c. 1894 Gustav Hammer & Co. commercial cooking machinery catalogue.]
* [http://www.clemson.edu/extension/hgic/food/food_safety/preservation/ Preserving foods ~ from the Clemson Extension Home and Garden Information Center]
* [https://web.archive.org/web/20111023191758/http://www.uga.edu/nchfp/ National Center for Home Food Preservation]
* [[BBC News Online]] – [https://news.bbc.co.uk/2/hi/americas/3915659.stm US army food... just add urine]
* [https://hearth.library.cornell.edu/ Home Economics Archive: Tradition, Research, History (HEARTH)] <br />An e-book collection of over 1,000 classic books on home economics spanning 1850 to 1950, created by Cornell University's [https://www.mannlib.cornell.edu/ Mann Library].
* {{cite web |first1=Sally |last1=Pobojewski |date=8 May 1995 |title=Underwater storage techniques preserved meat for early hunters |work=The University Record |publisher=University of Michigan |url=http://www.ur.umich.edu/9495/May08_95/storage.htm |access-date=28 September 2018 |archive-date=26 February 2019 |archive-url=https://web.archive.org/web/20190226001601/http://www.ur.umich.edu/9495/May08_95/storage.htm |url-status=dead }}

{{Food preservation}}
{{Cooking techniques}}
{{Consumer Food Safety}}
{{Authority control}}

[[Category:Food preservation| ]]
[[Category:Garde manger]]