Canning and Freezing

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Canning is a method of preserving food by first heating it to a temperature that destroys contaminating microorganisms, and then sealing it in air-tight jars, cans or pouches. Because of the danger of botulism and other pathogens, the only safe method of canning most foods is under conditions of both high heat and pressure, normally at temperatures of 240-250°F (116-121°C). Foods that must be pressure canned include all vegetables, meats, seafood, poultry, and dairy products. The only foods that may be safely canned in a boiling water bath (without high pressure) are highly acidic foods like fruits, pickled vegetables, or other foods to which acid has been added.

Contents 1 History 2 Canning companies 3 Canning organizations 4 External links

History

During the early Revolutionary Wars, the notable French newspaper Monde, prompted by the government, offered a hefty cash award of 12,000 Francs to any inventor who could come up with a cheap and effective method of preserving large amounts of food. The massive armies of the period required regular supplies of quality food, and so preservation became a necessity. In 1809, the French confectioner Nicolas François Appert developed a method of vacuum-sealing food inside glass jars. However, glass containers were unsuitable for transportation, and soon they had been replaced with cylindrical tin or steel cans. (Tin-openers were not to be invented for another thirty years - at first, soldiers either had to cut the cans open with bayonets or smash them open with rocks to get the food out.) The French Army began experimenting with issuing tinned foods to its soldiers, but the slow process of tinning foods and the even slower development stage, along with the difficulties of loading wooden wagons with tons of metal canisters, prevented the army from shipping large amounts around the Empire, and the war ended before the process could be perfected. Unfortunately for Appert, the factory which he had built with his prize money was burned down in 1814 by Allied soldiers invading France. Following the end of the Napoleonic Wars, the process was gradually put into practice in other European countries and in the United States. Based on Appert's methods of food preservation the packaging of food in sealed airtight tin-plated wrought-iron cans was first patented by an Englishman, Peter Durand, in 1810. Initially, the canning process was slow and labour-intensive, making the tinned food too expensive for ordinary people to buy. However, increasing mechanisation of the process, coupled with a huge increase in urban populations across Europe, resulted in a rising demand for tinned food.

A number of inventions and improvements followed, and by the 1860s, the time to process food in a can reduced from six hours to 30 minutes. Thomas Kensett established the first U.S. canning facility for oysters, meats, fruits and vegetables in New York in 1812 and also patented an improved tin canister method. Urban populations in Victorian era Britain demanded ever-increasing quantities of cheap, varied, good-quality food that they could keep on the shelves at home without having to go to the shops every day for fresh produce. In response, companies such as Nestle, Heinz, and others appeared to provide shops with good-quality tinned food for sale to ordinary working class city-dwellers. Demand for tinned food skyrocketed during the First World War, as military commanders searched for cheap, high-calorie food which could be transported safely, would survive trench conditions, and which would not spoil in between the factory and the front lines. Complete meals in a tin appeared in 1916, but throughout the war soldiers generally subsisted on very low-quality tinned foodstuffs, such as the British "Bully Beef" (cheap corned beef) and the notoriously disgusting "Pork and Beans" produced by the MacConnaughy Corporation. The tinned food issued to French soldiers was by far the worst in any army, whilst shortages of tinned food in the British Army in 1917 led to the government issuing soldiers with cigarettes and even amphetamines to suppress their appetites. After the war, companies that had supplied tinned food to national militaries improved the quality of their goods for sale on the civilian market. Canned foods were soon commonplace, and today tin-coated steel is the material most commonly used. Some food firms are currently dabbling with self-heating cans. Laminate vacuum pouches are also now used for canning, such as those found in an MRE.

Canning companies

• Hirzel Canning Company & Farms
• Contadina Foods, Inc
• BOBOLI Pty. Ltd
• Ball Corporation
• Crown Holdings Inc
• Silgan Containers Corporation
• Vanee Foods Company, Inc.

Canning organizations

• Can Manufacturers Institute
• Packaging Machinery Manufacturers Institute

External links

• National Center for Home Food Preservation - How do I...Can
• How to can fresh produce.
• The history of the Norwegian Canning Industry

This article is based on the article "Canning" from Wikipedia - the free encyclopedia created and edited by online user community. This article is distributed under the terms of GNU Free Documentation License. Here you find the list of authors of this article. The article can only edited within Wikipedia. Edit this article in Wikipedia.

In physics and chemistry, freezing is the process of cooling a liquid to the temperature (called freezing point) where it turns solid. Melting, the process of turning a solid to a liquid, is the opposite of freezing. Consequently the freezing point is the same temperature as the melting point. A pure substance has a fixed freezing point.

Freezing food for preservation

Freezing is a common method of food preservation which slows both food decay and the growth of micro-organisms and, by turning water to ice, makes it unavailable for bacterial growth and chemical reactions.

However, freezing only slows the deterioration of food: it does not stop it, and while it may stop the growth of micro-organisms, it does not necessarily kill them. Many enzyme reactions are only slowed by freezing, so it is often important to stop enzyme activity before freezing, either by blanching or by adding chemicals.

Foods may be preserved for several months by freezing, but not indefinitely. Long-term freezing requires a constant temperature of -18 °C or less. Some freezers cannot achieve, or are not kept at, that temperature. If the temperature in a freezer fluctuates, the length of time foods can be kept is reduced considerably less. Freezer doors should be kept closed as much as possible, and only a small amount of unfrozen food should be added at one time.

Freezing adversely affects the texture of many foods, and the texture of nearly all foods is damaged by thawing and re-freezing. Since water expands when it freezes, cell walls in food are often ruptured, resulting in food that is limp or pulpy when thawed. This is especially true of fruits and vegetables that have a high water content. Less damage is done to vegetables that are high in starch. Less damage is also done if the food is frozen quickly, so unfrozen food should be placed in the coldest areas, which are near the bottom of the freezer. Some additives, such as sugar or sorbitol, can hinder water's crystallization and preserve the food's cellular structure. Defects in the texture of thawed food can sometimes be obscured by cooking.

Ice cream is an example of a food which is intended for consumption while frozen.

American inventor Clarence Birdseye (1886-1956), who developed the quick-freezing process of food preservation in the early 20th century, is considered the father of the frozen-food industry.

See also: Food preservation, Flash freezing, Brain freeze, Supercooling

External links

• National Center for Home Food Preservation - How do I...Freeze

This article is based on the article "Freezing" from Wikipedia - the free encyclopedia created and edited by online user community. This article is distributed under the terms of GNU Free Documentation License. Here you find the list of authors of this article. The article can only edited within Wikipedia. Edit this article in Wikipedia.