A blast freezer is a freezer which is extremely cold. It may also be known as a shock freezer. Such freezers are intended to rapidly bring the temperature of foods down, freezing them extremely quickly. These specialized freezers are used in the frozen food industry for everything from ice cream to television dinners, and they are also utilized in some commercial kitchens for specialty tasks.
When food is frozen, the water inside it crystallizes. If freezing takes place at relatively warm temperatures, the ice crystals which form will be large. In a blast freezer, the extremely cold temperature promotes very rapid freezing, which creates small ice crystals. The smaller the crystals, the less damage to the food, as large crystals can rupture cells. Once the food has been frozen, it can be moved to a more conventional freezer for storage, as long as the freezer stays cold enough to keep the food frozen.
Many blast freezers operate with blowers which force chilled air over the food in the freezer to cool it down rapidly. Others may operate differently, depending on the design. These freezers can be equipped with movable trays for positioning foods, and they may also include an assortment of compartments for freezing. The freezer can usually handle foods which are chilled, at room temperature, or hot, as long as it is not overloaded; too high a volume of hot food, for example, can cause the temperature in the blast freezer to rise.
There's another advantage to blast or shock freezing, beyond the preservation of the integrity of the food. Extreme cold inhibits bacterial growth, which means that if food is handled safely and then placed immediately in the freezer, the likelihood of contamination is very low. This increases food safety, making such freezers popular in commercial food preparation to reduce the risk to consumers.
Blast freezers tend to eat up a lot of energy, which is why they are most commonly seen in industrial and commercial applications. Household cooks can use a blast freezer as well, if they have a need for it. For example, some hunters like to use a blast freezer to freeze meat once it has been butchered, and cooks who prepare a lot of dishes for future use, such as lasagnas, may also prefer the quality of shock frozen food.