Flash freezing

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System for fish conservation on the Kiel sea ​​fish market (1970)

The blast freezing or quick-freezing is used for gentle preservation of food in the production of frozen food . The temperature of the food to be frozen is lowered to the desired storage temperature (−18  ° C or lower) within a very short time (usually only minutes) . The process was developed by Clarence Birdseye in the early 20th century .

But only subsequent compliance with the frozen food chain in accordance with the frozen food ordinance, the avoidance of temperature fluctuations and protection against dehydration ensure the continued quality of the frozen food.

advantages

In contrast to the much slower freezing in the domestic freezer, the cell fluid only forms very small ice crystals when it cools down quickly . As a result, cell walls and membranes of organelles are not destroyed. Even when thawing, the cell structure is largely retained, the cells do not leak and certain ingredients (e.g. enzymes ) remain separated from the rest of the cell fluid in the organelles; Cell water and nutrients remain locked in, the internal pressure of the cell is retained. Therefore, the food does not lose its consistency. B. not muddy. Also other properties, e.g. B. the aroma development are also little affected.

When freezing slowly in the domestic freezer, problems that can be traced back to large ice crystals occur, especially with foods with a high water content or thin cell walls (e.g. berry fruits).

Procedure

For shock freezing depending on the type of food plate freezers , cold air freezers or cryogenic freezers used. All processes have in common that the product is either in direct contact with cold metal plates or that cold air or other gases flow around it at high speed.

Contact freezing process (plate freezer)

In this method, the packaged food is placed between metal plates in which a refrigerant flows that cools them down to -40 ° C. This removes heat from the products very quickly. This process is used for. B. with fish fillets and spinach .

Cold air freezing process

The products that are deep-frozen using this method are removed from heat in a tunnel by moving air at temperatures as low as −50 ° C. Lighter products are whirled up as a result (“flow-freezing process”). This method is used e.g. B. used in pasta .

Cryogenic process

This method uses the liquid refrigerants carbon dioxide and nitrogen . The carbon dioxide (-78 ° C) or nitrogen (-196 ° C) is sprayed into a tunnel system, in which the usually unpackaged food is transported on a belt. Solid ( dry ice ) and gaseous carbon dioxide is formed from liquid carbon dioxide at the moment it is sprayed in , which absorbs the heat from the refrigerated goods and is continuously extracted. The cryogenic processes are particularly suitable for meat and fish products as well as fruit and baked goods.

Individual evidence

1. ^ Ordinance on frozen foods ( TLMV ) of October 29, 1991, revised by the notice of February 22, 2007, last amended on December 13, 2011.
2. ↑ Quick-Frozen Food Exactly Like Fresh. Popular Science Monthly, September 1930, pp. 26-27.