Freezing :
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A slow temperature drop occurs as ice crystals form within the food. The temperature then drops more quickly as the crystals cool inside the food. Each food will freeze differently based on things like the amount of water, sugar, muscle tissue or air in the food. Rapid freezing improves the quality of the food.
The science of freezing foods Freezing is a quick and convenient way to preserve fruits and vegetables at home. Home frozen fruits and vegetables of high quality and maximum nutritional value can be produced done correctly.
Freezing. Freezing, in food processing, method of preserving food by lowering the temperature to inhibit microorganism growth. The method has been used for centuries in cold regions, and a patent was issued in Britain as early as 1842 for freezing food by immersion in an ice and salt brine.
Absolutely not! As long as it’s done properly, freezing food will lock in nutrients and freshness so your items are just as good as the day they went in the freezer. Does freezing food kill bacteria? Not exactly.
How to keep food from freezing?
Wrap and seal food tightly: Foil, plastic wrap and plastic freezer bags help protect food from freezer burn. Try to remove as much air when wrapping to prevent freezer burn.
According to the USDA, freezing food renders bacteria and other microbes inactive, thus preserving your food. Once the food is removed from the freezer and starts to thaw, bacteria and other microbes will become active again and you run the risk of foodborne illness if the items are left out between 40 and 140ºF before being washed and/or cooked.
If you’re freezing food for the first time, feel free to leave an inch and a half or two to see how much it expands.
Wrap and seal food tightly: Foil, plastic wrap and plastic freezer bags help protect food from freezer burn. Try to remove as much air when wrapping to prevent freezer burn. Or if you’re using food storage containers, make sure you’ve left enough space in the container for liquid to expand as it freezes.
Keep things cold: Make sure your freezer is 0°F. Use a refrigerator/freezer thermometer, like this one from LinkDm ($8) for accuracy.
While you can technically freeze almost anything, some foods freeze better than others. The top food groups for freezing are: Fruit. Blanched vegetables. Raw and cooked meat. Butter. Cookies—we always keep a batch of freezer-friendly cookies on hand to satisfy a sweet craving!
Fridge first: Don’t place glass jars directly in the freezer. Glass can shatter if the temperature changes too much too quickly, Place food in the fridge overnight before transferring to the freezer.
When did meat freeze?
In 1880 a cargo of meat shipped from Australia to Britain under refrigeration accidentally froze, with such good results that the process was at once adopted for long-distance shipments and other storage. In the 20th century quick, or flash, freezing was found to be especially effective with certain types of food.
Most commercial freezing is done either in cold air kept in motion by fans (blast freezing) or by placing the foodstuffs in packages or metal trays on refrigerated surfaces (contact freezing). For freeze-drying, see dehydration. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now.
Ordinary bread and rolls are rarely distributed and sold in frozen form because of the excessive cost in relation to product value, but a substantial percentage of all specialty products is sold in frozen form. Most bakery…. food preservation: Freezing.
Learn More in these related Britannica articles: Dehydration, in food processing, means by which many types of food can be preserved for indefinite periods by extracting the moisture, thereby inhibiting the growth of microorganisms.
Except for beef and venison, which benefit from an aging process, meat is frozen as promptly as possible after slaughter, with best results at temperatures of 0 °F (−18 °C) or lower. Fruits are frozen in a syrup or dry sugar pack to exclude air and prevent both oxidation and desiccation. Read More on This Topic.
The method has been used for centuries in cold regions, and a patent was issued in Britain as early as 1842 for freezing food by immersion in an ice and salt brine. It was not, however, until the advent of mechanical refrigeration that the process became widely applicable commercially.
What is the main source of food freezing?
Various refrigerants have been used for the compression–expansion system, which forms the major source of food freezing, probably 90% of all installations. Ammonia and sulfur dioxide are excellent media for the refrigeration process, but they carry the hazard of being inflammable and the risk of explosion.
In fast freezing, small intracellular crystals are formed inside the cell and are less damaging to the cells. In slow freezing, large extracellular ice crystals are formed between cells, which disrupt cell membranes and cause injury or death of the cells and thus are more damaging to the population of microorganisms. (2) There is an increase in viscosity of materials inside the cells as water is concentrated as ice crystals. (3) There is a loss of cytoplasmic gasses such as oxygen and carbon dioxide. (4) The pH value changes as a result of change of gasses in the cytoplasm. (5) The concentrations of cellular electrolytes increase, and alteration of cellular materials such as colloidal state of protein, denaturation of protein, temperature shock, and metabolic injury effects occur.
As temperature decreases, microbial metabolisms will be reduced. At freezing temperature, the activities of microorganisms are slowed and eventually stop. Chemical reactions are slowed but some food enzymes such as lipases can still be active. At lower temperature, metabolic activities are slowed.
In almost all food freezing applications, the freezing rate is determined by the rate at which latent and sensible heat can be transferred away from the food. Sensible heat is released throughout the food as it cools, while latent heat is released at the freezing front.
Drying or dehydration is one of the oldest methods in food processing. Originally, human beings used the sun to dry food and later used the process of dehydration by fire, hot air, and so on. Sun drying is an uncontrolled removal of water as the procedure depends on the availability of sun energy. It requires a large amount of space to spread out the food in thin layers horizontally or vertically and is inexpensive but subject to contamination by insects, rodents, birds, large and small animals, and human beings. Dehydration is removal of water from food under controlled conditions of temperature, humidity, air flow, and so on. It has economy of space and good sanitation, but it is far more expensive than sun drying. Foods involved include raisins, figs, nuts/grains, meats, fruits, and fish. The purposes for drying food are to prevent microbial growth and chemical deterioration, ease of storage, packing, and transportation. Some of the types of dryers are (1) heated air as the drying medium; (a) cabinet dryer in which hot air rises through the food and carries the moisture from the food in a cabinet; (b) tunnel dryer in which foods are placed on a conveyer belt and travel through a hot cannister (tunnel) where hot air removes moisture from the food as they pass through the tunnel; and (c) kiln dryer is similar to cabinet dryer but in a much larger scale. (2) Heat transfer through solid surface: (a) drum dryer. Products flow over the surface of heated stainless-steel drums. The products are dried and are scraped off with stationary blades, for example milk, fruits, vegetable juice, purees, and cereal; (b) vacuum shelf drying – uses lower temperature. As food is placed on heat shelves, a vacuum is applied which will allow moisture to leave the food at a lower temperature thus protecting the flavor and color of the food.
In slow freezing, large extracellular ice crystals are formed between cells, which disrupt cell membranes and cause injury or death of the cells and thus are more damaging to the population of microorganisms. (2) There is an increase in viscosity of materials inside the cells as water is concentrated as ice crystals.
The provision of low temperature for freezing is obtained from closed-circuit compression–expansion refrigeration systems, or by a cryogenic process of exposing the product to a cold atmosphere of liquid nitrogen or liquid carbon dioxide.
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