How freezing preserves food

Growth of almost all microorganisms slows dramatically at temperatures below freezing, or 32°F, and stops at temperatures below that—0°F or lower is optimal for freezing food. That said, microorganisms are not actually killed by freezing, and any microorganisms that are present in frozen food can reactivate upon thawing. In addition, enzymes that are naturally present in foods can continue to break them down, if very slowly, at freezing temperatures. Blanching or cooking foods before freezing them will inactivate most of the enzymes and kill other spoilers.