Frozen food

Freezing food preserves food from the time it is prepared to the time it is eaten. Since early times, farmers, fishermen, and trappers have preserved their game in unheated buildings during the winter season. Freezing food slows down decomposition by turning water to ice, making it unavailable for most bacterial growth. In the food commodity industry, the process is called IQF or Individually Quick Frozen.

A frozen processed foods aisle at a supermarket

Process

History

Clarence Birdseye, an American inventor, developed the quick-freezing system. He discovered that the combination of ice, wind, and low temperatures in the Arctic froze anything that was exposed to it almost instantly. Birdseye soon realized that the quick freezing effectively prevented large ice crystals from forming. Other attempts had resulted in the formation of large crystals, which destroyed the delicate cellular structure of the food. With only an electric fan, a few buckets of brine, and cakes of ice, Clarence Birdseye perfected his system of packing fresh food into waxed cardboard boxes and flash-freezing it under high pressure. He sold the patent to the Goldman-Sachs Trading Corporation (a subsidiary of Goldman Sachs & Company) and the Postum Company. In 1929 the first quick-frozen vegetables were sold to the public.

Preservatives

Frozen foods don’t require many preservatives because the process of preparing the food for freezing kills much of the bacteria living on the food. Carboxymethylcellulose (CMC) is used as a stabilizer in frozen foods because of its tasteless and odorless properties.

Packaging

Frozen food packaging must maintain its integrity throughout machine filling, sealing, freezing, storage, transportation, thawing, and often cooking. Most frozen foods are cooked in a microwave oven. To make it easier for the consumer, manufacturers have developed packaging that can go straight from freezer to microwave.

In 1974, the first differential heating container (DHC) was sold to the public. A DHC is a sleeve of metal designed to allow frozen foods to receive the correct amount of heat. Various sized apertures were positioned around the sleeve. The consumer would put the frozen dinner into the sleeve according to what needed the most heat. This ensured proper cooking.

Today there are multiple options for packaging frozen foods. Boxes, cartons, bags, pouches, heat-in-bag pouches, lidded trays and pans, crystallized PET trays, and composite and plastic cans.

Scientists are continually researching new aspects of frozen food packaging. Active packaging offers a host of new technologies that can actively sense and then neutralize the presence of bacteria or other harmful species. Active packaging can extend shelf-life, maintain product safety, and help preserve the food over a longer period of time. Several functions of active packaging are being researched:

• Oxygen scavengers
• Time Temperature Indicators and digital temperature dataloggers
• Antimicrobials
• Carbon Dioxide controllers
• Microwave susceptors
• Moisture control: Water activity, Moisture vapor transmission rate, etc.
• Flavor enhancers
• Oder generators
• Oxygen-permeable films
• Oxygen generators
• Validation of cold chain

With these new technologies, food may last longer and our knowledge about its safety will increase.

Effects on Nutrients

Vitamin Content of Frozen Foods

-Vitamin C: Usually lost in a higher concentration than any other vitamin. A study was performed on peas to determine the cause of Vitamin C loss. A vitamin loss of ten percent occurred during the blanching phase with the rest of the loss occurring during the cooling and washing stages. The vitamin loss was not actually accredited to the freezing process. Another experiment was performed involving peas and lima beans. Frozen and canned vegetables were both used in the experiment. The frozen vegetable were stored at -10 °F and the canned vegetables were stored at room temperature (75 °F). After 0, 3, 6, and 12 months of storage, the vegetables were analyzed with and without cooking. O'Hara, the scientist performing the experiment said, "From the view point of the vitamin content of the two vegetables when they were ready for the plate of the consumer, there did not appear to be any marked advantages attributable to method of preservation, frozen storage, processed in a tin, or processed in glass."

-Vitamin B₁ (Thiamin): A vitamin loss of 25 percent is normal. Thiamin is easily soluble in water and is destroyed by heat.

-Vitamin B₂ (Riboflavin): Not much research has been done to see how much freezing affects Riboflavin levels. One study found an 18 percent vitamin loss in green vegetables while another found a 4 percent loss. It is commonly accepted that the loss of Riboflavin has to do with the preparation for freezing rather than the actual freezing process itself.

-Vitamin A (Carotene): There is little loss of Carotene during preparation for freezing and freezing of most vegetables. However, there is a danger of losing the vitamin during a long-continued storage period.

Efficiency

Freezing is an effective form of food preservation because the pathogens that cause food spoilage are killed or do not grow very rapidly at reduced temperatures. The process is less effective in food preservation than are thermal techniques, such as boiling, because pathogens are more likely to be able to survive cold temperatures rather than hot temperatures. One of the problems surrounding the use of freezing as a method of food preservation is the danger that pathogens deactivated (but not killed) by the process will once again become active when the frozen food thaws.

Foods may be preserved for several months by freezing. Long-term frozen storage requires a constant temperature of -18 °C (0 °F) or less. Some freezers cannot achieve such a low temperature. The time food can be kept in the freezer is reduced considerably if the temperature in a freezer fluctuates; small ice crystals thaw as the temperature moves up, and refreeze onto larger crystals as the temperature declines. Fluctuations can occur by a small gap in the freezer door or adding a large amount of unfrozen food.

See also

• Refrigerator

References

• Arsdel, Wallace, B. Van, Michael, J Copley, and Robert, L. Olson. Quality and Stability of Frozen Foods: TIme-Temperature Tolerance and its Significance. New York, NY: John Wiley & Sons,INC, 1968.
• "Clarence Birdseye." Encyclopedia of World Biography. Vol. 19. 2nd ed. Detroit: Gale, 2004. 25-27. Gale Virtual Reference Library. Gale. Brigham Young University - Utah. Nov. 3 2009 <http://go.galegroup.com/ps/start.do?p=GVRL&u=byu_main>
• Copson, David. Microwave Heating. 2nd ed.. Westport, CT: The AVI Publishing Company, INC., 1975.
• Decareau, Robert. Microwave Foods: New Product Development. Trumbull, CT: Food & Nutrition Press, INC., 1992.
• Gould, Grahame. New Methods of Food Preservation. New York, NY: Chapman & Hall, 2000.
• Mathlouthi, Mohamed. Food Packaging and Preservation. New York, NY: Chapman & Hall, 1994.*^Robinson, Richard. Microbiology of Frozen Foods. New York, NY: Elsevier Applied Science Publishers LTD, 1985.
• Russell, Nicholas J., and Grahame W. Gould. Food Preservatives. 2nd ed. New York, NY: Kluwer Academic/Plenum Publishers, New York, 2003.
• Sun, Da-Wen. Handbook of Frozen Food Processing and Packaging. Boca Raton, Fl: Taylor & Francis Group, LLC, 2006.
• Tressler, Donald K., Clifford F. Evers, and Barbara, Hutchings Evers. Into the Freezer - and Out. 2nd ed. New York, NY: The AVI Publishing Company, INC., 1953.
• Tressler, Donald K., and Clifford F. Evers. The Freezing Preservation of Foods. 3rd ed. 1st volume. Westport, CT: The AVI Publishing Company, INC., 1957.
• Whelan, Elizabeth M., and Fredrick J. Stare. Panic in the Pantry: Facts and Fallacies About the Food You Buy. Buffalo, NY: Prometheus Books, 1998.