How did Clarence Birdseye's early plate-freezing method work?

Clarence Birdseye’s innovative method for freezing food relied on the principle of rapid heat removal to maintain product quality. His process involved placing packaged food between two refrigerated metal plates that were cooled to subfreezing temperatures by internally circulating refrigerants.12

By firmly pressing the packaged products between these plates, Birdseye achieved a highly efficient rate of heat transfer between the food and the cooling surface. This rapid freezing technique was particularly effective for preserving the original taste and texture of various items, including fish, fruits, and vegetables. Today, plate freezers continue to be used for flat or brick-shaped packaged products, such as fillets and various vegetables, by utilizing this same fundamental mechanism of direct contact with chilled metal surfaces.132