DEAR DR. BLONZ: Could you explain freezer burn, and whether foods that have suffered from it are safe to eat? I am particularly interested in whether it is safe to use freezer-burned foods such as beef, chicken or shrimp for soups or stews. -- S.T., Las Vegas
DEAR S.T.: Freezer burn describes the physical effect of a food losing moisture content from being in the freezer. In nature, there is a physical drive for substances in adjacent pools to mix and equilibrate. This even happens, albeit slower, at frozen temperatures.
In an attempt to equilibrate with the dry air of the freezer, the water content of a frozen food gets drawn to the surface and then pulled out. This involves sublimation: the process of a solid going directly to a vapor state without first passing through a liquid phase. Sublimation is integral to the freeze-drying process used with certain foods, but in the case of freezer burn, it is an undesirable side effect of frozen storage. This also explains why the ice in your ice cube tray shrinks over time.
The surface of an affected food will take on an “off” color and a leathery texture. Affected portions are safe to eat, but they won’t taste right. The formation and departure of the sharp-edged water/ice crystals are responsible for the rough texture in the “burned” foods.
The best way to protect against freezer burn is to pack your frozen foods in heavyweight, moisture-resistant wrap, such polyethylene freezer bags, aluminum foil, freezer film wraps or well-sealed plastic containers. Although they can hold liquids, standard plastic wraps can “breathe” a tiny bit, and that’s all it takes for moisture to escape in a dry, frozen environment. Brief uses of such wraps may be OK, but don’t trust them for longer than a week of freezer storage. Consider using plastic bags specifically labeled for freezer storage, since they have an additional barrier to prevent moisture loss.
You may, however, notice that even when using appropriate freezer containers or bags, some ice crystals will form in the non-food space during longer periods of storage. Do your best to make sure the bag or container is well sealed, with a minimum of dead space around the food. If you know it’s going to be there for a while, consider double-bagging.
Back to your issue: Depending on the degree of damage, you should be able to salvage these foods if you trim away the freezer-burned portions before cooking. If, as you say, all you want to do is to cut it up and use it in stocks, soups and stews, you may be able to salvage more, but I would proceed carefully to be sure you don’t have some undesirable textures in the final dish.
Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.