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Food Preservation.

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Food Preservation a) Canning The idea of canning is that it destroys any micro-organisms and their spores by applying heat. This is achieved by sterilising food within airtight containers to prevent re-contamination. The basic stages of canning are: * Filling the cans with product * Sealing the cans * Washing the cans * Sterilising the cans * Cooling the cans Food products that have been canned have very long shelf life and are stored at room temperature. b) Freezing Freezing is based on two ideas. Firstly, very low temperatures which inhibit growth of micro-organisms and reduce enzyme and chemical activity, and secondly the formation of ice crystals which draw available water away from food, therefore preventing the growth of micro-organisms. ...read more.


The product is scraped against a cooled surface and then immediately scraped away. iii. Cryogenic freezing: Liquid nitrogen (or CO2) is sprayed directly onto small food items such as soft fruits or prawns. It is due to the liquids' extremely low temperatures, -196oC and -78oC, which make freezing as a result almost instant. c) Drying Micro-organisms need water in order to grow and multiply. When moisture is reduced in food, micro-organism growth is reduced. Dehydration reduces the water activity level, weight and bulk of the food and helps to preserve the product. Dehydration is the reduction of water to prevent micro-organism activity. Many products, such as vegetables, are diced before drying - to increase their surface area - making water loss more rapid. ...read more.


This process is most commonly used to inhibit sprouting of vegetables, delay ripening of fruits or reduce numbers of micro-organisms which cause food poisoning. e) Chemical Preservatives This includes; Pickling Pickling vegetables and fruits with vinegar prevents the growth of micro-organisms. This is due to the food being placed in a low pH solution in which micro-organisms cannot grow. Sugar and Salt The addition of large quantities of sugar inhibits the growth of micro-organisms by making water unavailable. Jams, marmalades and jellies use this principle in their manufacture. Coating food in salt or placing it in a salt solution (brine) reduces the moisture content of the food, i.e. it reduces the availability of water to micro-organisms. With little moisture, micro-organism growth is reduced. However, the taste of the food may well be changed as a consequence. ...read more.

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