Flash freezing is a process in which food is very quickly frozen at extremely cold temperatures. In commercial processing, foods are flash frozen so that as many nutrients are retained as possible, and to make sure that the food is as fresh and flavorful as it can be. Some home cooks also practice a form of freezing to preserve foods like fruits and vegetables. This concept is also used in scientific and medical research to rapidly preserve specimens.
The concept of flash freezing was developed by Clarence Birdseye, who wanted to find a way to eat fresh vegetables in the winter and to move produce around without the risk of damage. He realized that freezing food at extremely cold temperatures well below the freezing point could be an excellent preservation method, and he turned the concept into a massive frozen foods company, inspiring other pioneers to do likewise.
On the industrial scale, this process is done in large freezers that get well below the freezing point. Foods are ideally frozen as soon as they are prepared or picked, and they freeze within only a few hours because the temperatures are so cold. Once flash frozen, the foods can be moved to a conventional freezer with a temperature closer to the freezing point, and they should stay frozen solid.
Fishing boats often use flash freezing to keep their catch as fresh as possible, especially if they are working in remote areas and will not be reaching port for days or weeks. In these cases, the fish are cleaned and then frozen as they are caught, and when the hold is full, the fish are offloaded for sale. This method is also used to preserve fruit and vegetable crops, and to preserve frozen meals that consumers can re-heat as needed.
Home cooks generally lack the equipment needed for real flash freezing, but they can fake it by freezing foods on a tray. By laying the food out to maximize exposure to the freezing temperatures in a home freezer, the cooks can encourage the food to freeze solid overnight. Keeping the freezer relatively empty to ensure that the air flows evenly over the food, and packing the food with ice, can help to ensure that it freezes properly. Once flash frozen, the individual pieces of food will also not be prone to sticking to each other, because they have been frozen independently, which can be extremely useful.