Freezing food is the process in which the vegetables temperature is reduced by freezing water in the cellular juices and interfacial distances of the tissue and converting it into ice crystals, which results in the concentration of dissolved substances in the non-freezing water and this reduces the water activity in the vegetables and the materials resulting from the freezing with deep temperatures of - 20 to -40 degrees Celsius.
It remains without physical or chemical changes for a long time, the preservative factor in this technique is by combining both low temperature and low water activity (Arising from the concentration of dissolved substances in a small amount of non-freezing water) and the steps that occur before freezing, such as boiling.
To preserve vegetables for a long time by preventing the growth of microorganisms at (-10C) or stop the chemical reactions and enzymatic activity at (-18C) and this may be available in household freezers, but when freezing on a commercial scale, the temperature is reduced to (-29C), so that the frozen food can be obtained in high quality.
The freezing industry has spread for a number of reasons:-
1) Preserve extra products from vegetables.
2) Availability in the off-season.
3) Easy operation, save time and cheap.
4) Improving the properties of the product during its preparation in terms of cleaning, peeling and sorting. Vegetables especially those eaten cooked represent a large sector of frozen vegetables. Egyptian standards specify some general conditions that must be met in the final frozen product.