Freezer burn
Encyclopedia
Freezer burn is a condition that occurs when frozen food
has been damaged by dehydration and oxidation, due to air reaching the food. It is generally induced by substandard (non-airtight) packaging.
The condition is primarily caused by sublimation. Water evaporates at all temperatures, even from what appears to be solid ice. When the constantly vibrating water molecules in the meats and vegetables stored in the freezer migrate to the surface, crystals of ice outside of the solid food are formed. The parts now deprived of moisture become dry and shriveled and look burned. In meats, air can cause fats to oxidize.
This process occurs even if the package has never been opened, due to the tendency for all molecules, especially
water, to escape solids via vapor pressure
. Fluctuations in temperature within a freezer also contribute to the onset of freezer burn because such fluctuations set up temperature gradient
s within the solid food and air in the freezer, which create additional impetus for water molecules to move from their original positions.
It is possible to slow down freezer burn by filling plastic containers with water (leaving room for expansion) and leaving them open in the freezer to help maintain humidity. Proper packaging can also help delay freezer burn because small, air-tight packaging allows local homeostasis
of humidity, and, to a lesser degree, temperature, although current available packaging cannot do this perfectly.
Meats and vegetables stored in a manual defrost freezer will last longer than those stored in automatic defrost freezers. That is because the temperature of a manual defrost freezer remains closer to 0 °F/-18 °C while the temperature of automatic defrost freezers fluctuates. Food with freezer burn, though dried and wrinkled, is safe to eat. However, food afflicted with freezer burn may have an unpleasant flavor. In most cases, it is sufficient to remove the parts affected by freezer burn.
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
has been damaged by dehydration and oxidation, due to air reaching the food. It is generally induced by substandard (non-airtight) packaging.
Cause and effects
Freezer burn is not a food safety risk. It appears as grayish-brown leathery spots on frozen food, and occurs when air reaches the food's surface and dries out the product. This can happen any time food is not securely wrapped in air-tight packaging. Color changes result from chemical changes in the food's pigment. Although undesirable, freezer burn does not make the food unsafe. It merely causes dry spots in foods.The condition is primarily caused by sublimation. Water evaporates at all temperatures, even from what appears to be solid ice. When the constantly vibrating water molecules in the meats and vegetables stored in the freezer migrate to the surface, crystals of ice outside of the solid food are formed. The parts now deprived of moisture become dry and shriveled and look burned. In meats, air can cause fats to oxidize.
This process occurs even if the package has never been opened, due to the tendency for all molecules, especially
water, to escape solids via vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
. Fluctuations in temperature within a freezer also contribute to the onset of freezer burn because such fluctuations set up temperature gradient
Temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degrees per unit length...
s within the solid food and air in the freezer, which create additional impetus for water molecules to move from their original positions.
It is possible to slow down freezer burn by filling plastic containers with water (leaving room for expansion) and leaving them open in the freezer to help maintain humidity. Proper packaging can also help delay freezer burn because small, air-tight packaging allows local homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
of humidity, and, to a lesser degree, temperature, although current available packaging cannot do this perfectly.
Meats and vegetables stored in a manual defrost freezer will last longer than those stored in automatic defrost freezers. That is because the temperature of a manual defrost freezer remains closer to 0 °F/-18 °C while the temperature of automatic defrost freezers fluctuates. Food with freezer burn, though dried and wrinkled, is safe to eat. However, food afflicted with freezer burn may have an unpleasant flavor. In most cases, it is sufficient to remove the parts affected by freezer burn.
See also
- "Whole body freezer burn", a related term used in cryonicsCryonicsCryonics is the low-temperature preservation of humans and animals who can no longer be sustained by contemporary medicine, with the hope that healing and resuscitation may be possible in the future. Cryopreservation of people or large animals is not reversible with current technology...
- Ice crystalsIce crystalsIce crystals are a small crystalline form of ice including hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. The highly symmetric shapes are due to depositional growth, namely, direct deposition of water vapour onto the ice crystal...
- Vacuum packingVacuum packingVacuum packing or vacuum packaging is a method of packaging that removes air from the package prior to sealing. It can involve both rigid and flexible types of packaging...
- Freeze dryingFreeze dryingFreeze-drying is a dehydration process typically used to preserve a perishable material or make the material more convenient for transport...
External links
- Ice crystals created in freezer burn and their relation to crystals in snow