Friday, June 10, 2011


It is wrongly assumed that frozen foods are convenience products because those who buy these products will vouch safe for the "ordeal" involved in cooking them. It is true that most frozen foods come pre-prepared requiring no efforts except for cooking but the recommended practice of thawing in a refrigerator can be time consuming negating the convenience factor very significantly. Fearing cross contamination and growth of undesirable microorganisms, room temperature thawing is generally frowned upon but recent studies have brought out the fact that thawing after immersing in water can cut down the thawing time considerably and this provides the consumer more opportunities to use frozen foods in day to day food preparations. Microwave oven is supposed to be handy in thawing but uneven heating make the product inferior for consumption. Water medium transfers heat much better than air and therefore it is logical to expect better results.

"Air-thawing in the refrigerator took 18 to 20 hours, while the room-temperature water bath thawed the steaks in about 20 minutes, and the hot-summer-day bath in 11 minutes. These water-bath times are so short that any bacterial growth would remain within safe limits. The water-thawed steaks actually leaked less juice than the air-thawed steaks. The researchers grilled the steaks, too, and found that all the thawed steaks lost about 26 percent of their original weight once cooked, while never-frozen steaks lost 21 percent. The study found no significant differences in tenderness between slow- and quick-thawed steaks. Eleven minutes is pretty quick, but Brian A. Nummer and colleagues at Utah State University in Logan shaved away another couple of minutes by heating the water bath to 140 degrees, the standard temperature of steam tables in food service kitchens. The Utah State group found that chicken breasts about a half-inch thick thawed in a little more than 3 minutes, and inch-thick breasts in less than 9 minutes. Although 140-degree water would eventually cook the chicken to medium-rare, they saw no signs of cooking. The quick-thawed breasts did lose slightly more juice than the refrigerator-thawed breasts, but when the chicken was grilled and served, a panel of 18 tasters was unable to tell them apart. And based on their mathematical modeling, the researchers concluded that any bacterial growth would remain well within safe limits. So there's no downside to quick-thawing steaks, chops, fillets and other relatively thin cuts in warm water right before cooking. Large roasts are a different story. They take long enough to thaw that there may be time for significant bacterial growth on their surfaces. Prompt cooking might well eliminate that problem, but until this has been studied, it's safest to continue thawing roasts in the refrigerator or in water under 40 degrees. Quick-thawing is easy to adopt in the home kitchen. But don't expect your thaw times to match the lab times I've quoted unless you have an immersion circulator or another method to keep the water in motion and at a constant temperature. If the water is still, a cold zone develops around the food and insulates it from the remaining warm water. And without infusions of hot water or heat from a burner, the icy food cools the water bath".

One of the problems of using water bath is the rapid cooling of layers of water in contact with the frozen pack hindering heat transfer and unless there is circulation of water around the frozen pack, thawing is bound to be slower. A common practice adopted in many kitchens is to change the water 2-3 times to accelerate the thawing rate. While the above findings may be true with thin slabs of meat, how far it is applicable to thawing of frozen vegetables or fruits may be uncertain. Of course common sense tells that being not so compact as meat, thawing these materials may be much less problematic.


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