What is Freeze burn ?
freezer burn describes only the loss of moisture (also termed as dehydration or desiccation) from the surface of frozen foods over time during frozen storage, yielding an opaque dehydrated surface.
These undesirable quality changes are exemplified by the toughening and discoloration of the surface of meat and poultry products, such as color changes in beef from red to brown and in skinless chicken breasts from pink to tan.
Freezer-burned food is safe to consume from a microbial perspective, but is of poor eating quality. If the freezer-burned area is not too extensive, you can simply cut the affected portion(s) off before or after cooking.
Science behind freeze burn
Moisture is lost from the surface of frozen food via sublimation, that is, the phase transition of ice directly to the vapor phase, without going through the liquid phase.
Sublimation is similar to evaporation; however, in the case of evaporation, water molecules transition from the liquid to the vapor state. Sublimation and evaporation take place at the surface, where molecules can escape (gain energy) or condense (lose energy).
If the solid or liquid is contained in a closed system at constant temperature, equilibrium between the vapor pressure of the solid or liquid surface and the container headspace is reached, where an equal number of water molecules leaves and returns to the surface. The vapor pressure of this equilibrium condition is called the saturated vapor pressure and is a function of temperature.
If the solid or liquid is contained in an open system at constant temperature, equilibrium is still attempted, but this time between the vapor pressure of the solid or liquid surface and the headspace of the entire room. In the case of an open system, “equilibrium” is often achieved by evaporation or sublimation of all the water or ice from the container.
The demarcation between sublimation (ice to vapor) and evaporation (liquid water to vapor) phase transitions is the triple point of water.
In summary, moisture transfer proceeds from ice at the surface of the food, via sublimation, to water vapor in the air of the freezer compartment, back to ice, via deposition, on the refrigerator coils.
Prevention from freeze burn
The best thing a consumer can do to keep the freezer from burning their food is to seal (or reseal) frozen food products properly and to consume the food within the recommended amount of storage time (for recommended storage times for quality).
Comments