Freezer burn

Freezer burn is a condition that occurs when frozen food has been damaged by dehydration and oxidation due to air reaching the food.

[1] It is generally caused by food not being securely wrapped in air-tight packaging.

Freezer burn appears as grayish-brown leathery spots on frozen food and occurs when air reaches the food's surface and dries the product.

[2] The food remains usable and edible, but removing the freezer burns will improve the flavor.

The lost water may then be deposited elsewhere in the food and packaging as snow-like crystals.