Why do packages of frozen food have printed on them the warning not refreeze?

When food is frozen, the water content within its cells turns into ice crystals. As these ice crystals thaw and then refreeze, they can change the composition and texture of the food, making it mushy or grainy. This is particularly noticeable with foods like fruits, vegetables, and fish, which have higher moisture content. Repeated cycles of freezing and thawing also accelerate the breakdown of cells, leading to a loss of nutrients and flavor.

Safety Concerns:

Refreezing partially thawed or previously frozen food can pose safety risks. During the thawing process, bacteria and other microorganisms that might have been present on the food can start to multiply. When the food is refrozen, these microorganisms can become trapped within the ice crystals and may not be completely killed during subsequent cooking. This can increase the risk of foodborne illnesses.