History of Research at the U.S. Department of Agriculture and Agricultural Research Service
Frozen Food That's Freezer Friendly
In the early years of frozen food, a whole host of complaints poured in about things like cardboard texture, funny color, and no taste. Some people also worried about lost nutrients and bacterial contamination during processing and storage.
Then ARS scientists began the Time-Temperature Tolerance Project. Building their own freezing facilities inside their lab, scientists experimented with every step in the process, from selection of the variety grown to harvesting, handling, blanching, freezing, packaging, storing, and transporting products to market.
What these scientists learned helped immeasurably to ensure the survival and growth of the U.S. frozen food industry.
In time, they devised nine principles for freezing vegetables. Producers still follow these cardinal rules today.
The Nine Principles for Freezing Vegetables
1. The product must be freezable. Peas freeze; cucumbers do not.
2. The variety must be suitable. Garden peas, for example, freeze better than peas grown for canning.
3. The raw product must be first-class. Freezing preserves defects as well as superior quality.
4. Handling between field and plant must be as prompt as possible.
5. Natural enzymes must be inactivated by blanching.
6. Freezing must be fast enough to ensure quality, yet economical enough to be competitive.
7. The plant must be kept sanitary and the line clean to prevent contamination by molds, yeasts, and bacteria.
8. Packaging must ensure that no moisture is lost during a year's storage.
9. Storage temperatures must be uniform, and never, never exceed 0 degrees F.
The Convenience Of Frozen Dinners
Not every fruit or vegetable responds to freezing well-strawberries and green beans, for example, do not. Juices leak from thawed strawberry cells and green beans lose texture. ARS researchers found that rapid freezing of berries and beans with liquid nitrogen resulted in much more satisfactory products.
Many processed foods also resist freezing. Back in the '50's, the first TV dinners were praised for their quick preparation time but often went uneaten because of their curdled gravies and sauces. ARS to the rescue! We substituted a flour made from waxy, or glutinous, rice for wheat flour to thicken the gravies. Sure enough, gravies stayed smooth after freezing. The same trick worked on frozen puddings, replacing the traditional cornstarch thickener.
You probably haven't heard of dehydrofreezing, a process in which fruits and vegetables are partially dehydrated before freezing to cut their weight in half. Its chief commercial use today is in freezing pieces of potatoes and apples for institutional use. But researchers are willing to bet its use will soon be expanded; keep an eye out in your supermarket's frozen food case!
"Frozen Food That's Freezer Friendly" was published in Science in Your Shopping Cart.