Freezing does not halt evaporation of the meat's fluids, it only retards it. Therefore, if the entire surface of the meat is not carefully covered with a moisture-proof (or at least moisture-resistant) wrap, some of the food's water, which is temporarily in a solid state, will evaporate. This direct transformation from ice to vapor is termed sublimation and produces what cooks call freezer burn.
The meat's covering should be sealed securely to prevent oxidation and to help ward off rancidity. Although the fat in any meat will eventually become rancid if stored long enough, the grace period is certainly long enough for normal requirements if the food is kept solidly frozen and not exposed to excess oxygen. A tight wrapping also helps prevent the meat from absorbing freezer odors.
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