Blast Freezing:

In blast freezers, fans blow and circulate cold air (normally minus 25 to minus 40 degrees F) over a product that has been placed in trays or on racks. Often the product is carried on conveyor belts through a horizontal tunnel or vertically in an ascending spiral. Tunnel belt speed varies with product size and form, Small rockfish fillets, for example, might pass through a blast freezer in 25 minutes, while a whole 20-lb. salmon might take four to six hours. Blast freezing can be used to freeze prepackaged items or individual and irregularly shaped products that would require further packaging prior to frozen storage. However, no boxes or other wrapping materials are necessary during blast freezing. A disadvantage to blast freezing is the potential for dehydration, which, in a poorly designed system, could equal 6 to 8 percent of the product's initial weight. A 1 percent weight loss is typical in a well-designed blast freezer. Surface dehydration can result in "freezer burn," evidenced by a whitish, cottony or spongy appearance of the flesh, especially along cut edges or on thin spots of the product.