Food Preservation

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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, yoghurt and pickled onions being common examples.

Food preservative technologies are accepted differently by consumers. In general, traditional technologies like pasteurisation are better accepted than nanotechnology for example. Contents

 1 Traditional techniques o 1.1 Drying o 1.2 Refrigeration o 1.3 Freezing o 1.4 Salt o 1.5 Sugar o 1.6 Smoking o 1.7 Pickling o 1.8 Lye o 1.9 Canning and bottling o 1.10 Jellying o 1.11 Jugging o 1.12 Subterrannean Burial o 1.13 Fermentation  2 Industrial/modern techniques o 2.1 Pasteurization o 2.2 Vacuum packing o 2.3 Artificial food additives o 2.4 Irradiation o 2.5 Pulsed electric field electroporation o 2.6 Modified atmosphere o 2.7 Nonthermal plasma o 2.8 High-pressure food preservation o 2.9 Biopreservation o 2.10 Hurdle technology  3 See also  4 Notes  5 References  6 External links Traditional techniques[edit]

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

Drying[edit]

Main article: Drying (food)

Drying is one of the most ancient food preservation techniques, which reduces water concentration sufficiently to prevent bacterial growth.

Refrigeration[edit]

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.

Freezing[edit]

Pictorial guide inside a freezer door Main article: 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 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.

Salt[edit]

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. Main article: Curing (food preservation)

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.

Sugar[edit]

Main article: Sugaring

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.

Smoking[edit]

Main article: Smoking (cooking) See also: List of smoked foods

Smoked Ham in a smokehouse in Schleswig-Holstein, Germany

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. 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.

Pickling[edit]

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 chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other micro-organisms. Typical pickling agents include brine (high in salt), vinegar, alcohol, and vegetable oil, especially olive oil 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 cucumbers, peppers, corned beef, herring, and eggs, as well as mixed vegetables such as piccalilli.

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.

Lye[edit]

Sodium hydroxide (lye) makes food too alkaline for bacterial growth. Lye will saponify fats in the food, which will change its flavor and texture. Lutefisk uses lye in its preparation, as do some olive recipes. Modern recipes for century eggs also call for lye.

Canning 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 Nicolas Appert.[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. 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 hygiene allowing contamination of canned food by the obligate anaerobe Clostridium botulinum, which produces an acute toxin within the food, leading to severe illness or death. This organism produces no gas or obvious taste and remains undetected by taste or smell. Its toxin is denatured by cooking, however. Cooked mushrooms, handled poorly and then canned, can support the growth of Staphylococcus aureus, which produces a toxin that is not destroyed by canning or subsequent reheating.

Jellying[edit]

Main article: Aspic

Food may be preserved by cooking in a material that solidifies to form a gel. Such materials include gelatine, agar, maize flour, and arrowroot flour. Some foods naturally form a protein gel when cooked such as eels and elvers, and sipunculid worms, which are a delicacy in Xiamen in Fujian province of the People's Republic of China. Jellied eels are a delicacy in the East End of London, where they are eaten with mashed potatoes. Potted meats in aspic, (a gel made from 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.

See also: Confit

Jugging[edit]

Main article: Jugging

Meat can be preserved by jugging, the process of stewing the meat (commonly 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.

Subterrannean Burial[edit]

Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool temperatures, pH level, or desiccants in the soil. Burial may be combined with other methods such as salting or fermentation. Most foods can be preserved in soil that is very dry and salty (thus a desiccant), or soil that is frozen.

Many root vegetables are very resistant to spoilage and require no other preservation than storage in cool dark conditions, for example by burial in the ground, such as in a storage clamp. Century eggs are 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.

Fermentation[edit]

See also: Fermentation (food) Some foods such as many cheeses, wines, and beers 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. Industrial/modern techniques[edit]

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

Pasteurization[edit]

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.

Irradiation[edit] Main article: Food irradiation

Irradiation of food[3] 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.[4][5] However, the wholesomeness of consuming such food is disputed by opponents[6] and consumer organizations.[7] 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.[8] 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.[9][10]

Pulsed electric field electroporation[edit]

Main article: 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.

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.

Carbon dioxide prevents insects and, depending on concentration, mold and oxidation from damaging the grain. Grain stored in this way can remain edible for five years.[citation needed]

Nitrogen gas (N2) at concentrations of 98% or higher is also used effectively to kill insects in grain through hypoxia.[11] 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%,[12] or so. This makes carbon dioxide preferable for fumigation in situations where a hermetic seal 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 32 to 36 degrees Fahrenheit. 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." [13]

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,[14] as well as having modern equivalents. The success of the method relies on have the correct mix of sealing, grain moisture, and temperature.[15]

A patented process uses fuel cells to exhaust and automatically maintain the exhaustion of oxygen in a shipping container, containing, for example, fresh fish.[16]

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.[17]

High-pressure food preservation[edit] Main article: Pascalization

High-pressure food preservation or pascalization refers to the use of a food preservation technique that makes use of high pressure. "Pressed inside a vessel exerting 70,000 pounds per square inch (480 MPa) 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 2005, the process was being used for products ranging from orange juice to guacamole to deli meats and widely sold.[18]

Biopreservation[edit]

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.[19] Beneficial bacteria or the fermentation products produced by these bacteria are used in biopreservation to control spoilage and render pathogens inactive in food.[20] It is a benign ecological approach which is gaining increasing attention.[19]

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.[21][22]

These days, LAB bacteriocins are used 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.[19]

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.[23] 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.[24] 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 preservatives or biopreservatives. 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.[23]

Principal hurdles used for food preservation (after Leistner, 1995)[25][26] 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]

Food portal

 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  Refrigerate after opening  Shelf-life

How to Choose a Method of Food Preservation

There are numerous ways to preserve food, many of which have been used for centuries and some, like refrigeration generated by electricity, that are very recent. This article provides you with some information on the different ways of preserving food, to help you decide which ways might work best for your glut of home-grown, caught or home-made produce.

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1. 1

Familiarise yourself with the reasons behind selecting any particular method of food preservation. Your choice of food preservation will depend on weighing up the advantages and disadvantages of each method. You should consider the following factors when deciding on which method to use:

o Space: The amount of space you have will definitely impact on your choice of preservation. Someone living in a farmhouse can probably store dozens of preserved fruits in jars, whereas someone living in an apartment is unlikely to have the space to spare for rows of preserved plums. o Climate: The climate can aid or hinder different storage methods. What might store beautifully through a Canadian winter may well rot during an Australian one. o Available equipment: Some preserving methods require specialised equipment that you may not have access to, or that you may be unwilling to use. For example, not everybody enjoys the sterilization process required to preserve fruit in jars and not everyone can build a smokehouse. o Cost: Naturally, the costs involved in preserving your food should be weighed against the cost of purchasing the food from a local market, supermarket or other source. In addition, there may be costs in using up storage space, costs in purchasing equipment etc. Care should be given, however, to include the benefits of enjoyment from preserving one's own food, as well as the health, environmental and nutrient benefits that might arise from preserving homegrown produce, costs that are very hard to quantify and should weigh heavily in your decision-making. o Nature of the food: Be realistic about the ability of the food to be preserved. Some food will not tolerate any form of preserving and needs to be eaten fresh. This means that you need to do your research. Also, some foods change during the preserving process and become less palatable or even take on characteristics that are less health-giving. For example, use of nitrites to preserve meat can turn healthy meat into a potentially carcinogenic product. o Hygiene and safety: Your ability to maintain a high level of hygiene and safety during the preservation process is important. If you cannot meet basic standards, it is best to not attempt a particular preservation method and to either substitute for a safer method or choose to not preserve the food. o Other issues: Perhaps there are health issues involved in preserving. For example, some people are unable to tolerate preservatives used to create dry fruit. Whilst it is possible to dry them organically, they will discolour and this may not be to the liking of some consumers.

Be aware of the different ways of preserving food. There are many possible ways to preserve food and each one has different considerations. As discussed in the previous step, it is important to assess each of the possible preservation methods that you might be considering using against the factors that are outlined above.

o Drying. Drying is an ancient technique of food preservation and works well for many food types. It is an inexpensive method of food preservation, as you rely on the sun or an oven. Dried foods are compact and easily stored or carried. The greatest disadvantages of drying food include loss of colour, loss of flavour and loss of vitamins. Some of these losses can be mitigated by not drying the food too long. o Salting: Salt is another ancient method of preservation. Salt can be used as part of the drying process. Salt increases the storage time of some foods such as fish and it enhances the flavour of dried foodstuffs. The use of a salt water brine is another common method of preservation and it has the benefit of stopping the growth of harmful organisms. Whilst it is possible to wash off excess brine or salt from salted food, this food will taste salty and the over- consumption of salt does carry a risk of disease. o Canning or bottling. This process requires canning equipment and the ability to use a heat source. Foods preserved by this method are sealed in a closed container, such as a can, glass jar or bottle. Such foods can be stored for up to a year. The cost of canning or bottling can be expensive after purchasing the equipment and use of heating fuel and it is a fiddly process requiring sterilization and knowledge of the temperatures involved. Canning cannot be done in an oven but must be done using a water or steam bath. There is a risk of severe food poisoning if this process is not followed properly, especially in the case of low-acid foods such as vegetables and meat. o Dehydration. There are many dehydration products on the market for a low price. Dehydration is a good means for making food small for storage or carrying on trips and it is easily restored to its original plumpness or juiciness through the addition of water. o Sugaring. Preserving through the use of tree saps or sugar is commonplace in some parts of the world. Trees such as the maple produce a syrup which is high in sugar and maple syrup can be stored for a long time. Sugar that is added to jams, jellies, relishes and preserves helps to lengthen the period of time that these condiments last. o Oil and fat. Some items can be stored in oil or fat. For example, herbs can be steeped in oil. o Live animals and plants. If there is room to grow plants and keep animals, this can be another method of preserving food. Naturally, there must be space and a knowledge of animal care is required. In some parts of the world, the possibility of an all-year round vegetable and fruit garden means that it is possible to be self- sufficient throughout the year without having to resort to other forms of preserving unless wished. o Curing and smoking. Drying using smoke can be used for meats, fish, cheese and nuts. Curing requires the addition of curing agents followed by smoking to preserve the food. Although smoked and cured meat can taste better, be aware that nitrates and nitrites can be carcinogenic. o Bin storage. If you have access to a cool, dark place, such as a cellar, it is possible to store foods for shorter periods of time just relying on the coolness of the room. Additional storage potential can be provided by storing items in bins filled with sand. o Pot-in-pot refrigeration. This method relies on the use of terracotta or clay pots that are lined with sand and kept cool through the addition of water. This method relies on evaporation and therefore only works in dry climates and it needs constant tending. This method of storage is best suited to places where electricity generation is not possible, such as selling locally grown produce at the market or in villages without refrigeration. The stored items should be consumed within a few days but the use of the pot-in-pot fridge helps to ensure that the goods remain in good, fresh condition during the time that they are stored and prevents decomposition during very hot weather. o Fermenting and pickling. Vegetables can be kept for several months using fermentation or pickling. Eggs can also be pickled to increase their shelf life. Pickles, sauerkraut and fermented soy bean curd are examples of such foods. On the downside, there is evidence that the acidic nature of pickled foods can lead to health problems if consumed too much. o Refrigeration and freezing. Naturally this requires access to electricity-generated refrigeration systems but if you have this, it is one of the easiest methods to store food. There are many guidelines available on how long food can be stored in refrigeration or in a freezer and you will even find some of these guidelines in individual wikiHows on particular food items. Downsides to this method include loss of food due to not knowing what is in your freezer or lack of dating items when you freeze them (thus necessitating throwing out items when you are not sure) and a tendency to over-stock refrigerators with food that goes off because nobody could consume it in time, or find it behind all the other food. Be vigilant in cleaning out the fridge weekly and the freezer monthly, so that you know what precious food you have stocked away. o Chiller bags. Chiller bags or thermal lunch bags are great for short- term preservation of food. Use them to transport food such as ice cream or other frozen products from the store to your home. Use thermal lunch bags to keep lunch cool during the morning until lunchtime. Neither of these options has a long duration of preservation; at tops usually about 3 - 4 hours. o Thermos flask. A thermos flask is good keeping food such as tea, coffee, soup or even sausages hot or cold for a few hours. As with the chiller bag, this is a very short-term option but useful for school, work and day hikes. 3. 3

Select your method. The method that suits you most may even be a combination of methods listed above, varying according to season and dependent on convenience. You might even choose to harvest a crop and use short and long term storage methods to enable you to use the crop now and into the future. Whatever drives your ultimate choice, be sure to observe all safety requirements and to label and date your preserved food if it is to be kept for a long period of time.

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 It is important to be aware of local laws and regulations regarding the preservation of food. For example, some countries regulate home usage of nitrites and nitrates in food production. Ask at your local government department if you are not sure.

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Recipes etc. with preservation explanations Related wikiHows

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Food preservation

Food can be preserved by removing one or more of the factors that bacteria and fungi need to survive. Methods of food preservation

Method Examples How it works Canning Vegetables The sealed can is heated to kill bacteria. When it cools, no more bacteria can enter. Method Examples How it works

Cooling or chilling

Ready made meals The food is kept at a low temperature (4°C) so bacteria cannot reproduce (they're not killed).

Freezing

Vegetables and meat products Bacteria cannot reproduce at low temperatures and the water in the food is frozen.

Drying

Fruit, flour, soups, pasta Removing water prevents the microorganisms from growing, or digesting the food.

Adding salt or adding sugar

Jam, crisps, meat Removes water by osmosis

Adding vinegar Pickles Changes the pH to prevent the enzymes in the microorganisms from working.

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Food Preservation: Methods of Preserving Food

The various actions of microorganisms result in the loss of edibility, texture, flavor, and nutritional value of food. By canning, pickling, or drying, the life span of some foods can be increased. To know about the different methods of food preservation and the principles they work on, read the following article. Advertisement

The nutrients that give us energy and help us maintain good health also cause our food to spoil. There are innumerable microorganisms in the atmosphere that derive their nutrition from these nutrients by breaking them into simpler forms. As these minute life forms start disintegrating the nutrients, they set off the process of food spoilage. With the knowledge of the role that microorganisms play in spoiling food, a number of methods of food preservation have been developed by man. All these methods work by altering conditions like temperature, availability of water or oxygen in the food, or in the environment in which the food is stored. Changing or altering these factors hinders the growth of these minute organisms, and hence prevents food spoilage.

Methods of Preserving Food

Food preservation is not just helpful in keeping the nutrients of food intact, but is also a smart way to cut down on costs. Here are a few technique that may come in handy. Drying

Red Chili Peppers

Squid

This is one of the oldest methods of food preservation. This process acts by reducing the moisture content in the food which in turn arrests bacterial growth. Drying is largely used for preserving meat. However, fruits and vegetables can also be preserved by this method. The additional advantage of drying is that it reduces the size and weight of the food product, therefore making it more portable. Sun drying, oven drying, and drying with the help of a dehydrator are the various ways used to reduce the water content of food.

Freezing and Refrigeration

Frozen Vegetables

Refrigerated Produce

Microorganisms require a certain level of temperature for their survival. Freezing foods lowers the temperature to levels that make the environment unsuitable for microbial growth. This is the principle on which home refrigerators work. Cold stores are used to preserve large amounts of food stuff for a longer period of time, so that they can be used during a natural calamity or national emergency. The only drawback of this food preserving technique is its dependence on electricity.

Canning and Bottling

Bottled Vegetables

Canned Vegetables

In this process, the food is first processed and then sealed in airtight containers. While the microorganisms are killed by processing the food, their entry and proliferation is restricted by canning it in an airtight environment. The various methods used to process the food before it is canned are pasteurization, boiling, freezing or vacuum treatment.

Vacuum Treatment

Green Olives

In this method food is stored in airtight containers that strips bacteria of the oxygen that helps it carry on with its metabolism. Hence, the growth of these microorganisms is arrested and food is preserved. Nuts are usually preserved by this method.

Curing (Salt)

Meat

Salt is a natural food preservative that draws out moisture from the food as well as from the cells of the microorganisms that may be present in it. Lack of moisture kills these organisms and hence prevents food spoilage. Salt is commonly used as a preservative in meat products.

Pickling

Mixed Pickles

Cucumber, beef, peppers, and some vegetables may be preserved by pickling. This technique involves dipping the food in some liquid chemical that prevents the growth of microorganisms but still maintains edibility of the food. The preserving liquids used are vinegar, brine, alcohol, and some other oils. This process is known as chemical pickling. The other way of pickling is by fermentation. In fermentation pickling, the preservation agent is produced by the food itself during the process of fermentation.

Pasteurizing

Milk

This is a process where liquid food is preserved. Before, pasteurization was done to combat the souring of local wines, however, it is mostly done to milk now. The milk is heated for 15 to 30 seconds at around 158°F as the bacteria present in the milk will get killed. Then, it is quickly cooled at 50°F in order to prevent the rest of the bacteria from growing. The next step is to store the milk in sterilized bottles and stored in a cool place.

Oil and Vinegar Preserving

Vegetables

Oil and vinegar are common in Italian cooking. However, this isn't the only place where the duo is utilized. The mixture of oil and vinegar is used to prevent the growth of microorganisms that spoil the food. So vegetables and fruits are preserved in them so they can last for a longer time.

Smoking

Fish

This is a very simple method where perishable food items are smoked in order to increase their shelf life. The food, mostly fish and meats, is cured (salting) and then exposed to smoke created via wood. Certain fruits and vegetables can also be smoked and preserved.

Fermenting

Sauerkraut

Indian Pickles

The process of fermentation was not invented, but discovered. Certain foods such as cheeses, wines, and beers can be preserved for a long time as their production is done by specific microorganisms. They fight against less benign organisms that spoil the food. In this process, beginner microorganisms, salt, hops, temperature control, and specific oxygen levels are used to create conditions that will help the organisms produce food which is fit for our consumption.

Jam

Jam and Marmalade

Preserving fruits is an age-old process that is still continued worldwide. The fruits are boiled so that the moisture content is reduced and the unwanted bacteria are killed. Then, the process of sugaring is done in order to prevent any regrowth of bacteria, followed by sealing the final product in an airtight, sterilized jar. The final step is vital as it prevents the jam from getting contaminated.

Sugar

Apples

Sugaring is used to preserve fruits like apples, apricots, and plums in sugary syrup that dehydrates the foods. The skin of certain fruits are cooked in sugar till they crystallize and then they are stored in a dry environment. One drawback of this method is that sugar itself draws moisture. Once the amount of moisture in sugared foods rise, it might reach the level congenial for microbial growth.

These are a few of the healthy ways to preserve food. Most of these can be domestically used to delay food spoilage. In other methods, ionizing radiation, high pressure, and even controlled growth of certain bacteria are used to fight the decaying action of microorganisms. By Debopriya Bose Last Updated: July 12, 2013

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