Freezing food

Fuchigami, M., Miyazaki, K., and Hyacumoto, N. (1995). Frozen carrots texture and pectic components as affected by low-temperature-blanching and quick freezing. ]. Food Sci. 60, 132-136. 

Freshly cut oranges or their juices may be exposed in an open glass for several hours without appreciable loss of I he vitamin because of the protective effect of the acids present and the practical absence of enzymes that catalyze its destruction. In potatoes, when baked or boiled, there is a slight loss of the vitamin, blit if they are whipped lip with air while hot, as in the production of mashed potatoes, a large fraction of the initial vitamin content usually will be lost. In freezing foods, it is common practice to dip them in boiling water or to treat them briefly with steam to inactivate enzymes, after which they arc frozen and stored at very low temperatures. In this state, the vitamin is reasonably stable. Vuamin C degradation in dehydrated food systems is described shortly. 

Liquid nitrogen is used to freeze foods such as TV dinners. Many frozen foods commonly found in grocery stores are produced this way. IMAGE COPYRIGHT 2009, ANTHONY BERENYI. USED UNDER LICENSE FROM SHUTTERSTOCK.COM. 

Reid, D.S. Fundamental physicochemical aspects of freezing, Food Technol., 37, 110, 1983. 

Freezing Foods should be stored and conserved in the proper temperature, usually below 5°C. Bacteriae, which are the main etiology of food borne infection, grow in temperatures ranging between -tlO and h-65°C. 

Adding heat to reactants helps break bonds and increases the speed at which molecules and atoms are moving. The faster they move, the more likely it is that they will collide and react. Removing heat slows down reactions. That s why freezing food might help keep it from spoiling as quickly. 

Analyzing Why is it necessary to liquefy air to 2. Inferring Why do you think liquid nitrogen is separate its components used to freeze food ... 

Two famous American companies made major contributions to food preservation in the early 20th century. Clarence Birdseye, known as the "father of frozen food," adapted a method of freezing food that he learned from Eskimos meat frozen in the extreme cold of midwinter actually keeps better than any other preserved meat, frozen or otherwise. In 1923, he perfected the process of flash-freezing foods under high pressure, and the modern frozen food industry was born. 

Several methods can be used to rapidly freeze foods. The most efficient is to immerse the product in a veiy cold liquid. This permits a liquid-solid interface for rapid heat transfer. Liquid nitrogen (LNj) and liquid Freon freezant (LFF) are the most commonly used, the latter being the most popular because... 

Therefore, HPSF can be especially usefnl to freeze foods with large dimensions where the effects of freeze cracking caused by thermal gradients can become prononnced (Martino et al., 1998). 

Two simple principles govern the process of freezing the food must be as fresh as possible and it should be frozen rapidly. Fast-freezing limits the disruption of a food s cell structure—although no matter how fast and efficiendy you freeze food its structure will inevitably break down a frozen raspberry will never look the same as a fresh one. A freezer should operate at - 0.5° F (-18° C) or below. At this temperature, the bacteria that spoil food cannot grow. 

Zhong W., Chang G.-S., Zhang H. 2008. Review on applications of the quick-freezing food stabilizers. Grain Distribution TechnoL 2008-01. 

Because of its low reactivity, large quantities of N2 are used as an inert gaseous blanket to exclude O2 in food processing, manufacture of chemicals, metal fabrication, and production of electronic devices. Liquid N2 is employed as a coolant to freeze foods rapidly. 

What effect does freezing food have on reaction rates Why is freezing used for preservation of food, tissue samples, and biological samples ... 

Ice also sublimes out of frozen foods. You can clearly see this in food that is frozen in an airtight plastic bag for a long time. The ice crystals that form in the bag are water that has sublimed out of the food and redeposited on the smface of the bag. For this reason, food that remains frozen for too long becomes dried out. This can be avoided to some degree by freezing foods to colder temperatures (further below 0 0, a process called deep-freezing. The colder temperature lowers the rate of sublimation and preserves the food longer. 

Shock-freeze food, e.g. meat or fish, in tunnel, spiral or rotary freezers Cool food during mixing, chopping and transport (e.g. by mixing dry-ice pellets or CO2 snow into the product)... 

Nitrogen is essential for life, but it is also useful in many other ways. That is why about 2500 tonnes of it are produced in Britain every day, by fractional distillation of liquid air. The gas is used for filling spaces in food packages and oil tanks. Liquid nitrogen is very cold, so is used for freezing food. Other uses are given on page 101. 

Frozen foods that are allowed to thaw and then are refrozen usually lose considerable in quality, and possibly some in nutritive value. In addition, it means that the food cannot be held as long in the freezer. When freezing fresh, unfrozen foods, divide into portions that will be needed, so that it is not necessary to thaw the whole piece in order to use a portion of it. The common rule of thumb is to freeze foods only twice. This means that the food can be thawed, prepared and refrozen until it is needed. Or it can be thawed, prepared and served, and any large amount left over can be refrozen to be used at a later date. Foods cannot be held as long if frozen twice as they can if frozen only once. 

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