Flash freezing

One of the most fascinating topics discussed in "NOVA: Absolute Zero" was the history of quick freezing. It was invented by Clarence Birdseye in 1924 while he was ice fishing. The temperature was so cold that when he caught a fish, it immediately froze upon exiting the water. Afterwards, when he went to cook the fish it still tasted as if it were fresh and had never been frozen. Before this discovery, if food had been frozen, it was frozen through a slow process which resulted in a not very appealing texture and flavor. The best food was fresh. Birdseye discovered that this was due to the crystals formed during the slow freezing process. The water crystals formed were large and ended up breaking the cell membranes within the food. In turn, when the food thawed, all of the water would leak out of the food and it would become mushy and loose its flavor. A quick freeze, on the other hand, kept the crystals that formed small, therefore, when the food thawed, the cell membranes were not ruptured and the texture and flavor were not compromised. He patent two ways of quick freezing food: the first involved taking packaged food and holding it between two metal plates and cooled to between -40 and-45 degrees Fahrenheit using a calcium chloride solution. The second patent utilized pressure and ammonia to cool food. The packaged food was placed between two metal plates under pressure and cooled to -25 degrees Fahrenheit by evaporating ammonia. Quick freezing is still used in refrigeration units. However, some companies use liquid nitrogen to quickly and efficiently cool their products. This cryogenic cooling of products has been termed flash freezing.

https://www.loc.gov/rr/scitech/mysteries/frozenfood.html

https://en.wikipedia.org/wiki/Frozen_food