Sometimes a small amount of a frozen food is needed, like a few strawberries for a smoothie, one chicken breast, or a few pepper slices for a soup. By “flash freezing” or using the “tray pack” method, one can easily remove just the right amount of fruit, vegetable, meat, and even baked items needed, rather than thawing larger amounts of food all at once.
In the food industry, flash freezing quickly chills food items at extremely low temperatures with circulating air. This quick-chill method keeps ice crystals small, preserving the cell structure and preventing moisture loss in the food when it thaws. In the home, flash freezing refers to the tray pack method or practice of freezing individual pieces of food separately spread out on a baking sheet or tray until firm (1-2 hours). When frozen firm, the frozen food is promptly packaged (use containers or bags specific for freezing to prevent freezer burn), leaving no head space, sealed, labeled, and returned to the freezer. This prevents individual pieces of food from fusing together during freezing.
Small ice crystals are desirable in frozen food to preserve texture. Large ice crystals rupture food cells and cause a soft, mushy texture. Small crystals are formed when food is frozen quickly and kept at a constant storage temperature of 0ºF (-18ºC) or lower, making the at-home tray pack method desirable for any foods that come in or can be cut or broken into individual pieces. Raw, cooked, or blanched foods may be frozen using the tray pack method.
Foods that can be Flash Frozen with the Tray Pack Method
Bacteria, molds, and yeast are present on all fresh foods and multiply rapidly between temperatures of 40°F and 140°F (4°C and 60°C). Therefore, fresh fruits and vegetables should be washed with cool water to remove dirt and residues and prepared appropriately, including blanching when necessary, prior to freezing. Other foods should be handled appropriately for their type. Freezing does not kill most microorganisms in food but prevents their growth. When thawed, the surviving organisms on any frozen food can grow again.
- Fresh fruits: strawberries, blueberries, blackberries, raspberries, cherries, mango chunks, cranberries, grapes, bananas slices, pineapple chunks, peach slices, kiwi slices, gooseberries, currants, rhubarb. Fruits that darken, such as peaches, can be pre-treated with ascorbic acid and drained prior to freezing.
- Fresh vegetables that do not need blanching prior to freezing: peppers and chilies (seeded, whole, halved, or chopped), onions and garlic (chopped), tomatoes (peeled). [See Freezing Onions, Peppers, and Tomatoes]
- Fresh vegetables that have been blanched, cooled, and drained prior: green/yellow beans, shelled peas, zucchini/summer squash, whole-kernel corn, carrots, okra, sugar/snap peas and small mixed vegetables. [See How to Blanch and Freeze Vegetables]
- Individual portions of meat or chunks of meat.
- Individual scoops of cookie dough.
- Unbaked, shaped yeast dough. [See Freezing Yeast Dough]
- Individual portions of baked items.
Trays or baking sheets may be lined with a silicone baking mat (Silpat) or parchment paper if sticking or freezing to the metal is of concern. To ensure that there is sufficient cold air to circulate around the trays to freeze quickly and not raise the temperature of already frozen food, add no more than 2 pounds of food per square foot of freezer space.
Food stored at temperatures of 0°F or below will always be safe to eat. Freezing prevents the growth of the microorganisms that cause food-borne illness. However, frozen foods might lose flavor, texture, or overall quality over time. The FDA Refrigerator and Freezer Storage Chart lists optimum freezing times for the best quality of most foods. Other recommendations from StillTasty.com for items not on the list include:
- Baked items – 3-6 months
- Unbaked yeast dough – 1 month
- Cheesecake slices – 2 weeks
- Fruit – 1 year
- Cookie dough – 3-4 months
With the exception of most yeast dough products, it’s best to plan ahead and thaw frozen food in the refrigerator, where it will remain at a safe, constant temperature — at 40°F (4°C) or below. Other options include thawing in cold water or in the microwave. It’s also safe to cook foods from the frozen state; frozen vegetables are commonly prepared this way. Frozen fruit can be served frozen as snacks or used in salads or desserts.
The Mayo Clinic favors flash-freezing of produce, indicating that studies have shown that fruits and vegetables that are appropriately prepared and frozen as quickly as possible retain nutrients better.
For more information on freezing foods, check out The Science of Freezing Foods by the University of Minnesota Extension.