Food preservation

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Food preservation usually involves preventing the growth of bacteria, fungi (such as yeasts), or any other micro-organisms (although some methods work by introducing benign bacteria or fungi to the food), as well as retarding the oxidation of fats that cause rancidity. Food preservation can also include processes that inhibit visual deterioration, such as the enzymatic browning reaction in apples after they are cut, which can occur during food preparation.

Many processes designed to preserve food will involve a number of food preservation methods. Preserving fruit by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture content and to kill bacteria, yeasts, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination). There are many traditional methods of preserving food that limit the energy inputs and reduce carbon footprint.[1]

Maintaining or creating nutritional value, texture and flavour is an important aspect of food preservation, although, historically, some methods drastically altered the character of the food being preserved. In many cases these changes have come to be seen as desirable qualities – cheese, yogurt and pickled onions being common examples.

Traditional techniques[edit]

Techniques of food preservation available to the home chef, ranging from since the dawn of agriculture up until the Industrial Revolution.


Main article: Drying (food)

Drying is one of the oldest techniques used to hamper the decomposition of food products. As early as 12,000 B.C. Middle Eastern and Oriental cultures were drying foods using the power of the sun. Vegetables and fruit are naturally dried by the sun and wind, but in the Middle Ages, "still houses" were built in areas that didn't have enough sunlight to dry things. A fire would be built inside the building to provide the heat to dry the various fruits, vegetables, and herbs.[2]


Main article: Refrigeration

Refrigeration preserve foods by slowing down the growth and reproduction of micro-organisms and the action of enzymes that cause food to rot. The introduction of commercial and domestic refrigerators drastically improved the diets of many in the Western world by allowing foods such as fresh fruit, salads, and dairy products to be stored safely for longer periods, particularly during warm weather.


Pictorial guide inside a freezer door
Main article: Frozen food



Bag of Prague powder #1, also known as "curing salt" or "pink salt." It's typically a combination of salt and sodium nitrite, with the pink color added to distinguish it from ordinary salt.

Salting or curing draws moisture from the meat through a process of osmosis. Meat is cured 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 Clostridium botulinum. It was a main way of preservation in the medieval times.


Main article: Sugaring

The earliest cultures have used sugar as 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.[2] "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."[3] Sugar is used to preserve fruits, either in an anti-microbial syrup with fruit such as apples, pears, peaches, apricots, plums 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 citrus fruit (candied peel), angelica and ginger.


Main article: Smoking (cooking)

Smoking is used to lengthen the shelf life of perishable food items. This effect is achieved by exposing the food to smoke from burning plant materials such as wood. Smoke deposts a number of pyrolysis products onto the food, including the phenols syringol, guaiacol, catechol.[3] These compounds aid in the drying and preservation of meats and other foods.Most commonly subjected to this method of food preservation are meats and fish that have undergone curing. Fruits and vegetables like paprika, cheeses, spices, and ingredients for making drinks such as malt and tea leaves are also smoked, but mainly for cooking or flavoring them. It is one of the oldest food preservation methods, which probably arose after the development of cooking with fire.


Main article: Pickling

Pickling is a method of preserving food in an edible anti-microbial liquid. Pickling can be broadly categorized into two categories: chemical pickling and fermentation pickling.


In fermentation pickling, the food itself produces the preservation agent, typically by a process that produces lactic acid. Fermented pickles include sauerkraut, nukazuke, kimchi, surströmming, and curtido. Some pickled cucumbers are also fermented.



Canning and bottling[edit]

Preserved food
Main article: Canning
See also: Home canning

Canning involves cooking food, sealing it in sterile 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.[4] 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 microorganisms, food spoilage, and illness.[2]

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 fruits such as tomatoes 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.



Main article: Aspic


See also: Potted shrimps


See also: Confit


Main article: Jugging


Subterrannean Burial[edit]


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 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 in the fall in northern farms in the USA for preservation. Some methods keep it crispy while other methods produce sauerkraut[citation needed]. 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.

In Orissa, India, it is a practice to store rice & paddy by burial under the earth. this method helps to store for 3-6months in dry season.


The earliest form of curing was dehydration. Often salt to added to accelerate this process. In the culinary world it was common to choose raw salts from various sources (rock salt, sea salt, etc).[2] More modern "examples of salts that are used as preservatives include sodium chloride (NaCl), sodium nitrate NaNO3 and sodium nitrite (NaNO2). Even at mild concentrations (up to 2%) sodium chloride (which is present in many food products) is capable of neutralizing the antimicrobial character of natural compounds."[3]



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 resulting alcohol kills any bacteria in the water that could make you sick. Additionally, the water now has the nutrients from the barley and other ingredients, and the microorganisms can also produce vitamins as they ferment.[2]

Industrial/modern techniques[edit]

Techniques of food preservation developed in research laboratories for commercial applications.


Main article: 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 to 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 Louis Pasteur in 1862.

Vacuum packing[edit]

Main article: 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, slowing spoiling. Vacuum-packing is commonly used for storing nuts to reduce loss of flavour from oxidation.

Artificial food additives[edit]

Main article: Preservatives

Preservative food additives can be antimicrobial, which inhibit the growth of bacteria or fungi, including mold, or antioxidant; such as oxygen absorbers, which inhibit the oxidation of food constituents. Common antimicrobial preservatives include calcium propionate, sodium nitrate, sodium nitrite, sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.) and disodium EDTA. Antioxidants include BHA and BHT. Other preservatives include formaldehyde (usually in solution), glutaraldehyde (kills insects), ethanol, and methylchloroisothiazolinone.


Main article: Food irradiation

Irradiation of food[5] is the exposure of food to ionizing radiation; either high-energy electrons or X-rays from accelerators gamma rays (emitted from radioactive sources as Cobalt-60 or Caesium-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. However, it is fundamentally different from pasteurization, as it reduces the microbial load by incremental (logarithmic) steps, whereas in heat treatment the observation of a minimum temperature and minimum duration of exposure ensures the elimination of the microorganisms under consideration.

The irradiation process is unrelated to nuclear energy, but it may use the radiation emitted from radioactive nuclides produced in nuclear reactors. Ionizing radiation is hazardous to life (hence its usefulness in sterilisation); 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 receives any radiation dose from the facility. Irradiated food does not become radioactive, and national and international expert bodies have declared food irradiation as wholesome.[6][7] However, the wholesomeness of consuming such food is disputed by opponents[8] and consumer organizations.[9] 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.[10] Irradiation may allow lower-quality or contaminated foodstuffs to be rendered marketable.

It is estimated that about 500,000 tons of food items are irradiated per year worldwide in over 40 countries. These are mainly spices and condiments with an increasing segment of fresh fruit irradiated for fruit fly quarantine.[11][12]

Pulsed electric field electroporation[edit]

Main article: Electroporation


Modified atmosphere[edit]

Main article: 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 carbon dioxide (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 vitamins. Grains may be preserved using carbon dioxide by one of two methods: Either a block of dry ice is placed in the bottom and the can is filled with grain or the container is purged from the bottom by gaseous carbon dioxide from a cylinder or bulk supply vessel.


Nitrogen gas (N2) at concentrations of 98% or higher is also used effectively to kill insects in grain through hypoxia.[13] However, carbon dioxide has an advantage in this respect, as it kills organisms through hypercarbia and depending on concentration hypoxia and, requiring concentrations of above 35%,[14] or so. This makes carbon dioxide preferable for fumigation in situations where a hermetic seal cannot be maintained.


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,[16] as well as having modern equivalents. The success of the method relies on have the correct mix of sealing, grain moisture, and temperature.[17]


Nonthermal plasma[edit]

Main article: 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.[19]

High-pressure food preservation[edit]

Main article: Pascalization



3D stick model of nisin. Some lactic acid bacteria manufacture nisin. It is a particularly effective preservative
Main article: Biopreservation

Biopreservation is the use of natural or controlled microbiota or antimicrobials as a way of preserving food and extending its shelf life.[21] Beneficial bacteria or the fermentation products produced by these bacteria are used in biopreservation to control spoilage and render pathogens inactive in food.[22] It is a benign ecological approach which is gaining increasing attention.[21]

Of special interest are lactic acid bacteria (LAB). Lactic acid bacteria have antagonistic properties that make them particularly useful as biopreservatives. When LABs compete for nutrients, their metabolites often include active antimicrobials such as lactic and acetic acid, hydrogen peroxide, and peptide bacteriocins. Some LABs produce the antimicrobial nisin, which is a particularly effective preservative.[23][24]


Hurdle technology[edit]

Main article: Hurdle technology

Hurdle technology is a method of ensuring that pathogens in food products 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.[25]

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 products.[26] The organoleptic quality of the food refers to its sensory properties, that is its look, taste, smell, and texture.


Principal hurdles used for food preservation (after Leistner, 1995)[27][28]
Parameter Symbol Application
High temperature F Heating
Low temperature T Chilling, freezing
Reduced water activity aw Drying, curing, conserving
Increased acidity pH Acid addition or formation
Reduced redox potential Eh Removal of oxygen or addition of ascorbate
Biopreservatives Competitive flora such as microbial fermentation
Other preservatives Sorbates, sulfites, nitrites

See also[edit]


  2. ^ a b c d e Nummer, B. (2002). “Historical Origins of Food Preservation” (Accessed on May 5, 2014)
  3. ^ a b c Msagati, T. (2012). “The Chemistry of Food Additives and Preservatives”
  5. ^ anon., Food Irradation - A technique for preserving and improving the safety of food, WHO, Geneva, 1991
  9. ^ Consumers International - Home[dead link]
  10. ^ NUCLEUS - Food Irradiation Clearances
  11. ^ Food irradiation - Position of ADA J Am Diet Assoc. 2000;100:246-253
  15. ^ Controlled Atmospheric Storage (CA) :: Washington State Apple Commission
  17. ^ Annis P.C. and Banks H.J. 1993. Is hermetic storage of grains feasible in modern agricultural systems? In “Pest control and sustainable agriculture” Eds S.A. Corey, D.J. Dall and W.M. Milne. CSIRO, Australia. 479-482
  18. ^ Laine Welch (May 18, 2013). "Laine Welch: Fuel cell technology boosts long-distance fish shipping". Anchorage Daily News. Retrieved May 19, 2013. 
  19. ^ NWT magazine, December 2012
  20. ^ "High-Pressure Processing Keeps Food Safe". Archived from the original on 2008-02-02. Retrieved 2008-12-16. "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." 


External links[edit]