Because freezing does not kill harmful bacteria. As food thaws, harmful bacteria grow and multiply again.
The refrigerator is the recommended method for thawing. Four to five pounds of meat requires 24 hours to thaw. While food can be thawed outside the refrigerator by immersion in cold water, the water must remain cold to prevent bacterial growth. Consequently, the water either should remian running or should be replaced every half hour.
Foods can also be thawed in the microwave, though, cooking should follow immediately to prevent bacteria from growing on the surface.
