Food Preservation is the process of treating and handling food to stop or to slow down spoilage and maintain nutritional value, density, texture and flavor. Preservation usually involves preventing the growth of bacteria,
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 preservation include drying, spray drying, freeze drying, freezing, vacuum-packing, canning and preserving in syrup, sugar crystallization, food irradiation, adding preservatives or inert gases such as carbon dioxide, other method that not only help to preserve food, but also add flavor, include pickling, salting, smoking, and curing.
Preservation processes include:
- Heating to kill or denature organisms (e.g. boiling).
- Oxidation (e.g. use of sulfur dioxide).
- Toxic inhibition (e.g. smoking, use of carbon dioxide, vinegar, alcohol etc.).
- Dehydration (drying).
- Osmotic inhibition (e.g. smoking, use of carbon dioxide, vinegar, alcohol etc.).
- 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.
One of the oldest methods of food preservation is drying, which reduces water activity to delay or prevent bacterial growth. Most types of meat can be dried. Many fruits can also be dried; The process is often applied to apples, pears, bananas, mango's, papaya, apricot, coconut, Zante currants, sultanas, raisins and 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.
Meat, fish and some other foods may be both preserved and flavored through the use of smoke-house. The combination of heat to dry the food without cooking it, and the addition of the aromatic hydrocarbons from the smoking preserves the food.
Freezing is also one of the most commonly used processes. It is used commercially and domestically for preserving a wide range of food stuffs including prepared food stuffs. For example, potato waffles are stored in freezer, but potatoes 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 stores food in a vacuum environment, usually in an airtight 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 and Sugar:
Salting or curing draws the 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.
Pickling is a method of preserving food by placing it or cooking it in a substance that inhibits or kills bacteria and other microorganisms. 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 and other oils.
Most pickling processes 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.
Sodium hydroxide (lye) makes food too alkaline for bacterial growth. Lye saponifies fats in the food, which change its flavor and texture.
Canning And Bottling:
Canning 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 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 through canning or bottling is at immediate risk of spoilage once the can or bottle is opened.
Lack of quality control in the canning process may allow ingress of water or microorganisms as a result the can swells or bursts. There have been examples of poor manufacture and poor hygiene allowing contamination of canned food by the obligate, Clostridium botulinum, which produces toxin within the food leading to severe illness or death. This organism produces no gas or obvious taste and therefore can not be detected by taste or smell. Food contaminated in this way includes corned beef and tuna.
Food may be preserved by cooking in a material that solidifies it and form a gel. Such materials include gelatin, agar, maize flour and arrowroot flour.
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 animals own blood is sometimes added to the cooking liquid. Jugging was a popular method of preserving meat until the middle of the 20th century.
Irradiation of food 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 Cesium-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. Like 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 does not relate to nuclear energy, but it may use the radiation emitted from radioactive nuclides produced in nuclear reactors. Ionizing radiation is hazardous to life, therefore, 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.
Irradiation as 'wholesome' UN-organization as WHO and FAO are endorsing to utilize food irradiation. International legislature on whether food may be irradiated or not varies worldwide from no-regulation to full banning. It is estimated that about 500000 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.
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 ba°s with an atmosphere modified to reduce the oxygen (O2) 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 "buiped" of excess gas. The carbon dioxide from the sublimation of the dry ice prevents insects, mold, and oxidation to damage the grain. Grain stored in this way can remain edible for five years.
Nitrogen gas (N2) 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 at concentration of only 80% or so. This makes carbon dioxide preferable for fumigation in situations where a hermetic seal cannot be maintained.
Many root vegetables are very resistant to spoilage and require no other preservation except storage in cool dark conditions, usually in field clamps.
Some foods, such as cheeses, will keep for a long time without use of any special procedures. The preservation occurs because of the presence of very high numbers of beneficial bacteria or fungi, which use their own biological defenses to prevent other organisms attack.