Various preserved foods
'Food preservation' is the process of treating and handling
food in such a way as to stop or greatly slow down spoilage to prevent
foodborne illness while maintaining
nutritional value, density, texture and
flavor.
Preservation usually involves preventing the growth of
bacteria,
fungi and other
micro-organisms, as well as retarding the
oxidation of
fats which cause
rancidity. It also includes processes to inhibit natural aging and discolouration that can occur during food preparation such as the
enzymatic browning reaction in apples which causes browning when apples are cut. Some preservation methods require the food to be sealed after treatment to prevent re-contamination with microbes; others, such as drying, allow food to be stored without any special containment for long periods.
Common methods of applying these processes include
drying,
spray drying,
freeze drying,
freezing,
vacuum-packing,
canning, preserving in syrup, sugar crystallisation,
food irradiation, adding
preservatives or inert
gases such as carbon dioxide. Other methods that not only help to preserve food, but also add flavor, include
pickling,
salting,
smoking, preserving in
syrup or
alcohol,
sugar crystallisation and curing.
Preservation Processes
Preservation processes include:
★ Heating to kill or denature organisms (e.g. boiling)
★ Oxidation (e.g use of sulphur dioxide)
★ Toxic inhibition (e.g. smoking, use of carbon dioxide, vinegar, alcohol etc)
★ Dehydration (drying)
★ Osmotic inhibition ( e.g use of syrups)
★ Low temperature inactivation (e.g. freezing)
★ Ultra high water pressure (e.g. fresherized, a kind of “cold” pasteurization, the pressure kills naturally occurring pathogens, which cause food deterioration and affect food safety.)
★ Many combinations of these methods
★
Chelation
Drying
One of the oldest methods of food preservation is by drying, which reduces water activity sufficiently to delay or prevent
bacterial growth. Most types of meat can be dried. This is especially valuable in the case of pig meat, since it is difficult to keep without preservation. Many fruits can also be dried; for example, the process is often applied to apples, pears, bananas, mangos, papaya, apricot, and coconut.
Zante currants,
sultanas and
raisins are all forms of dried grapes. Drying is also the normal means of preservation for cereal grains such as wheat, maize, oats, barley, rice, millet and rye.
Smoking
Meat, fish and some other foods may be both preserved and flavoured through the use of smoke, typically in a smoke-house. The combination of heat to dry the food without cooking it, and the addition of the aromatic hydrocarbons from the smoke preserves the food.
Freezing
Freezing is also one of the most commonly used processes commercially and domestically for preserving a very wide range of food stuffs including prepared food stuffs which would not have required freezing in their unprepared state. For example, potato waffles are stored in the freezer, but potatoes themselves require only a cool dark place to ensure many months' storage. Cold stores provide large volume, long-term storage for strategic food stocks held in case of national emergency in many countries.
Vacuum packing
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, hence preventing the food from spoiling. Vacuum-packing is commonly used for storing
nuts.
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.
Sugar
Sugar is used to preserve fruits, either in syrup with fruit such as
apples,
pears,
peaches,
apricots,
plums or in crystallised form where the preserved material is cooked in sugar to the point of crystralisation and the resultant product is then stored dry. This method is used for the skins of
citrus fruit (candied peel),
angelica and
ginger. A modification of this process produces
glacé fruit such as glacé
cherries where the fruit is preserved in sugar but is then extracted from the syrup and sold, the preservation being maintained by the sugar content of the fruit and the superficial coating of syrup. The use of sugar is often combined with alcohol for preservation of luxury products such as fruit in
brandy or other spirits. These should not be confused with fruit flavoured spirits such as
Cherry Brandy or
Sloe gin
Pickling
Pickling is a method of preserving food by placing it or cooking it in a substance that inhibits or kills bacteria and other micro-organisms. This material must also be fit for human consumption. Typical pickling agents include
brine (high in
salt),
vinegar, ethanol, and
vegetable oil, especially
olive oil but also many other oils. Most pickling processes also involve heating or boiling so that the food being preserved becomes saturated with the pickling agent. Frequently pickled items include
vegetables such as
cabbage (to make
sauerkraut and
curtido),
peppers, and some animal products such as
corned beef and
eggs.
EDTA may also be added to
chelate calcium. Calcium is essential for bacterial growth.
Lye
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 and
hominy use lye in their preparation, as do some olive recipes.
Canning and bottling
Preserved food
involves cooking
fruits or
vegetables, sealing them in sterile cans or jars, and
boiling the containers to kill or weaken any remaining bacteria as a form of
pasteurization. Various 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. Many vegetables 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 and poor
hygiene allowing contamination of canned food by the obligate , ''
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. Food contaminated in this way has included
Corned beef and
Tuna.
Jellying
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 the town of
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
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.
Irradiation
Irradiation of food
[1] is the processing of food with
ionizing radiation; either high-energy
electrons or
X-rays from accelerators, or by
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. Irradiation is not effective against viruses or
prions, and is only useful for food of high initial quality.
As any other technology it is not a panacea and cannot resolve food problems in general. Only food of high initial quality is suitable for radiation processing; a spoiled food cannot be reverted to un-spoiled. Irradiation is not effective against viruses and prions; it cannot eliminate toxins already formed by microorganisms.
The radiation 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; for this reason irradiation facilities have a heavily shielded irradiation room where the process takes place. Radiation safety procedures ensure that neither the workers in such facility nor the environment receive any radiation dose from the facility. Irradiated food does not become radioactive, and national and international expert bodies have declared food irradiation as wholesome. However, the wholesomeness of consuming such food is disputed by opponents and consumer organizations.
[2] National and international expert bodies have declared food irradiation as 'wholesome'; UN-organizations as WHO and FAO are endorsing to utilize food irradadiation. International legislature on whether food may be irradiated or not varies worldwide from no regulation to full banning.
[3]
It is estimated that about 500,000 tons of food items are irradiated per year world-wide in over 40 countries. These are mainly
spices and
condiments with an increasing segment of fresh fruit irradiated for fruit fly quarantine
[4][5].
Modified atmosphere
Modified atmosphere is a way to preserve food operating on the atmosphere around it. Salad crops which are notoriously difficult to preserve are now being packaged in sealed bags with an atmosphere modified to reduce the oxygen (O
2) concentration and increase the
carbon dioxide (CO
2) 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. A block of
dry ice is placed in the bottom and the can is filled with grain. The can is then "burped" of excess gas. The
carbon dioxide from the sublimation of the dry ice prevents insects,
mold, and
oxidation from damaging the grain. Grain stored in this way can remain edible for five years.
Nitrogen gas (N
2) at concentrations of 98% or higher is also used effectively to kill insects in grain through
hypoxia. However, carbon dioxide has an advantage in this respect as it kills organisms through both hypoxia and hypercarbia, requiring concentrations of only 80%, or so. This makes carbon dioxide preferable for fumigation in situations where an
hermetic seal cannot be maintained.
Clamps
Many root vegetables are very resistant to spoilage and require no other preservation other than storage in cool dark conditions, usually in field
clamps.
Biological processes
Some foods, such as many traditional
cheeses, will keep for a long time without use of any special procedures. The preservation occurs because of the presence in very high numbers of beneficial bacteria or fungi which use their own biological defences to prevent other organisms gaining a foot-hold.
Fresherized process
An ultra-high pressure food preservation technique using water pressure of approximately 50-100,000 pounds per square inch, equivalent to 3-6 times the pressure found at the bottom of the ocean. A kind of “cold” pasteurization, the pressure kills naturally occurring pathogens, which cause food deterioration and affect food safety.
Fresherized food is different than other methods of food preservation which use heat pasteurization and chemical additives. The taste, texture and naturally occurring vitamins are equal to “freshly made” food. In addition, the amount of energy used for fresherized foods is relatively low, compared to food preservation methods that require heat.
See also
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Food manufacturing
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Food engineering
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Chutney
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Food processing
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Jam
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Marmalade
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Pickling
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Shelf life
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Fresherized
Notes
1. anon., Food Irradation - A technique for preserving and improving the safety of food, WHO, Geneva, 1991
2. http://www.consumersinternational.org/homepage.asp
3. http://nucleus.iaea.org/NUCLEUS/nucleus/Content/Applications/FICdb/FoodIrradiationClearances.jsp?module=cif
4. http://www.mindfully.org/Food/Irradiation-Position-ADA.htm
5. C.M. Deeley, M. Gao, R. Hunter, D.A.E. Ehlermann, The development of food irradiation in the Asia Pacific, the americas and Europe, Rad.Phys.Chem. (in press); tutorial presented to the International Meeting on Radiation Processing, Kuala Lumpur, 2006
References
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★
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External links
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National Center for Home Food Preservation
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BBC News Online -
US army food... just add urine
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Food Preservation at
How Stuff Works
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