When you take things out of the freezer, they can smell different for several reasons:
Temperature: The most immediate and noticeable reason is the change in temperature. When you take an item out of the freezer, it rapidly warms up to room temperature. Higher temperatures can increase the rate of evaporation of volatile compounds present in the item, leading to a more intense and noticeable aroma.
Volatile compounds: Many foods and substances contain volatile compounds that contribute to their distinct smell. These compounds can be sensitive to temperature changes and might evaporate or become more volatile when exposed to higher temperatures. This increased volatility makes the smell more perceptible.
Degradation and oxidation: Freezing can alter the structure of some molecules in food or other items. When you thaw them, these molecules might undergo chemical changes due to degradation or oxidation, leading to the release of new compounds with distinct odors.
Food packaging: The materials used for packaging can sometimes absorb or trap odors during freezing. When the item is taken out of the freezer, these trapped odors might be released, contributing to the perceived change in smell.
Microbial activity: Freezing can slow down or inhibit microbial growth in food. When you remove the item from the freezer and it starts to thaw, any remaining microbial activity can resume, potentially leading to the production of new odorous compounds.
Perception: Cold temperatures can numb our olfactory senses, reducing our ability to perceive certain odors fully. When the item warms up, our sense of smell becomes more sensitive, making the odor seem stronger or different than when it was frozen.
It's essential to note that not all items will exhibit a significant change in smell when taken out of the freezer. The extent of the difference will depend on the specific item, its composition, and the freezing and thawing conditions.