advantages and disadvantages of slow and quick freezing

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Freezing is a longer-term method of preserving food. Freezing uses two controls to prevent the growth of bacteria The liquid is converted to a solid (ice) and is therefore unavailable to bacteria The low temperatures reduce the rate of bacterial growth Together these controls allow food to be stored for long periods. It is important to remember that the bacteria have not been destroyed. On thawing they will become active again Freezing

During freezing, the time factor is critical. If freezing is slow, large ice crystals will form, damaging the cell walls of the food :

During freezing, the time factor is critical. If freezing is slow, large ice crystals will form, damaging the cell walls of the food Quick freezing = small crystals Slow freezing = large crystals

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The rate of freezing depends upon number of factors , such as The method employed The temperature Circulation of air or refrigerant Size and shape of packages and kind of food

Slow Freezing or Sharp Freezing:

Slow Freezing or Sharp Freezing Usually refers to freezing in air with only natural air circulation or at best with electric fans. The temperature is usually -23.3 C or lower but may vary from -15 to -29 C, and freezing may take from 3 to 72 hr. Slow cooling permits the flow of water from the cells to the outside , thereby promoting extracellular ice formation instead of lethal intracellular freezing. This method has been successfully employed for cryopreservation of meristems of peas , potato , cassava , strawberry etc.

Quick Freezing or Rapid Freezing:

Quick Freezing or Rapid Freezing Quick freezing is a method of increasing the shelf life of perishable foods by subjecting them to conditions of temperature low enough to inhibit the oxidative enzymatic and microbial changes. which are responsible for the changes in flavor and color of foods.

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Food is frozen in a relatively short time Freezing time takes 30 min or less and usually the freezing of small packages or units of food. Food quickly frozen from 0 > -18°C in approximately 12 minutes. Creates smaller ice crystals & less damage to the food. The food retains its shape & texture with this method.

Quick freezing is accomplished by one of three general methods::

Quick freezing is accomplished by one of three general methods: Direct immersion of the food or the packaged food in a refrigerant, as in the freezing of fish in brine or of berries in special syrups. Indirect contact with the refrigerant, where the food or packaged is in contact with the passage through the refrigerant at – 17.8 to -45.6C flows, Air –blast freezing , where frigid air at -17.8 to -34.4C is blow across the materials being frozen .

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Ice Crystal Size Quick freezing Slow freezing

The advantages claimed for quick freezing over slow freezing are that:

The advantages claimed for quick freezing over slow freezing are that Smaller ice crystals are formed, hence there is less mechanical destruction of intact cells of the food, There is a shorter period of solidification and therefore less time for diffusion of soluble materials and separation of ice, there is more prompt prevention of microbial growth, and There is more rapid slowing of enzyme action.

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Heat is removing so quickly that there is little time for dehydration of the cells and ice will be formed inside the cells numerously as small ice crystals Product quit similar to original unfrozen specimen as there is minimum dislocation of water Quick frozen products have better taste, flavor, aroma, color appearance and freshness than slow frozen products. High nutritive value and less time in cooking 100% edible portion of food available in each packages More highgenic and more convenient to handle Little scope for adulteration, when packaged and sealed.

Disadvantages of quick freezing:

Disadvantages of quick freezing Higher investment in deep freezer or freezing equipment or frozen stores. Thawing problems in some cases Need for refrigerated display cabinets for retail marketing Freezing technology at present suitable for upper and middle class Products are more prone to dehydration because of large exposed surface. Small fluctuation in storage temperature can result in thawing into a large lump.

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Slow freezing( lowering temp by 1 c/ min) kills only some pathogens and forms large ice crystals causing mechanical destruction to the intent cells of food and also water will not able to its original position during thawing and will lose some amount of water… but in the case of quick freezing ,it kills all fewer pathogens and maintain uniformity in extra or intra cellular water and form small ice crystals which helps in less damages to food products . “ so quick freezing is better than slow freezing ” Conclusion


Reference Crystallization-process in freezing storage Quick freezing preservation of foods principles practices R & D needs- J.S. Pruthi Food microbiology- William c. Frazier Wikipedia

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