The change in smell when food is frozen, refrigerated, or at room temperature is primarily due to the effects of temperature on the volatility of aroma compounds in the food.
Freezing: When food is frozen, the extremely low temperatures cause a significant reduction in the mobility of molecules, including aroma compounds. As a result, the release of volatile compounds that contribute to the food's aroma is greatly diminished. This leads to a dampened or muted smell when the food is frozen. Additionally, freezing can cause some chemical reactions that alter the composition of aroma compounds, further affecting the overall smell.
Refrigeration: Refrigeration, at a temperature above freezing but still relatively low, slows down the rate of evaporation of aroma compounds compared to room temperature. Some volatile compounds may still escape, but at a much slower pace. This slower release of aromas can give the impression of a less intense smell compared to when the food is left at room temperature.
Room Temperature: At room temperature, the mobility of molecules, including aroma compounds, is higher. As a result, volatile compounds are more readily released into the air, leading to a more pronounced and noticeable smell of the food.
It's essential to note that different food items can react differently to temperature changes. Some foods, when frozen, may retain their aroma relatively well, while others might lose their characteristic smell more significantly. Similarly, certain foods can develop new aromas or off-flavors as a result of temperature changes and storage conditions.
Moreover, factors like packaging and exposure to air can also influence how the aroma of food changes during storage. Some containers might trap the aroma, while others could allow it to dissipate more easily.
Overall, the impact of temperature on food aroma is a complex interplay of chemical reactions, volatility, and the physical state of the food. Understanding these factors can help you make better storage decisions to preserve the desired qualities of different food items.