How does blast freezing differ from contact freezing?

In the context of food preservation, blast freezing and contact freezing are two primary methods used to lower the temperature of food to inhibit microorganism growth.1

Blast Freezing
This method utilizes cold air kept in motion by fans to remove heat from the surface of the food as rapidly as possible. In industrial settings, such as air-blast tunnels or belt freezers, precooled air at approximately −40 °C is blown over the products. This technique is commonly used for a wide variety of items, including packaged meals, poultry, and bakery goods.213

Contact Freezing
In contrast, contact freezing involves placing foodstuffs—often in packages or on trays—directly onto refrigerated surfaces. Plate freezers are the standard equipment for this process, where products are firmly pressed between metal plates cooled by internally circulating refrigerants. This method is particularly effective for flat or brick-shaped products, such as fish fillets, beef patties, and various vegetables, as it facilitates high rates of heat transfer through direct contact.123