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Blanching operations are designed to expose the entire product to high temperatures for a short period of time. The primary function of this operation is to inactivate or retard bacterial and enzyme action, which could otherwise cause rapid degeneration of quality. Two other desirable effects of blanching include the expelling of air and gases in the product, and a reduction in the product volume.
Field of application
Blanching is an important step in the processing of green vegetables and fruits.
Techniques, methods and equipment
Depending on the product and/or availability of equipment, blanching may be accomplished by direct or indirect heating systems. Direct heating is normally made by immersion in hot water (80 to 100°C) or exposure to live steam. The operation is normally carried out in horizontal chambers. The residence time in the blancher can vary from approximately 1 minute to 5 minutes depending on the vegetable or fruit being blanched. For some products direct contact with water is to be avoided thus heat exchangers working with hot water or vapour are applied.