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ABOUT CRYOGENICS
ADVANTAGES
THE PROCESS


 

 
THE PROCESS
 
Cryogenic freezing is an upcoming food processing technology that is gaining popularity because of the lower setup costs and improved food quality when compared to mechanical freezing.

Cryogenic food freezing differs widely from mechanical ammonia of Freon freezing systems. Thus, it requires a different procedure in determining the final exit temperature of a certain food product. Cryogenic freezing involves freezing the outer layers of the food beyond its actual freezing point, while the inner part of the product remains warm. The product's final temperature is not its temperature as it exits the cryogenic tunnel. . Only after full equilibration or equalization is its final temperature known. This usually occurs after up to 15 minutes later, Innovative cryogenic freezing technologies can be used to produce high quality frozen foods.

To obtain the maximum refrigeration benefit, a typical CO2 system will inject CO2 throughout the length of the freezer. In N2 systems, the N2 is sprayed into the freezer and separates as liquid and vapor. As droplets touch the product surface, the liquid changes to vapor, and in the process, extracts latent heat from the food surface. The vapor distribution through the freezer creates convective currents that increase the freezing rate. In this case, about 50% of the refrigeration effect is supplied by the N2 phase change from liquid to vapor. The remaining heat is removed by the N2 vapor flowing through the freezer. It should be noted that heat removal would not induce phase change by itself: additional factors such as the rate of formation of ice crystals and the propagation of these in the food structure are involved.

The freezing of food materials is more complex than the freezing of pure water. All food materials contain solutes such as carbohydrates, salts, colorants and other compounds which affect their freezing behavior. Most food products contain animal and/or vegetable cells forming biological tissues. The water content of these tissues is either inside the cells (intracellular fluid) or surrounding these (extra cellular fluid). Since the lowest concentration of solutes is found in the extra cellular fluids, the first ice crystals are formed there. During a slow freezing, there will be time for the cell to lose water by diffusion and the water will freeze on the surface of the crystals already formed. As the cells keep losing water, the cell shrinks more and more until it collapses. The large ice crystals will exert pressure on the cellular walls, causing drip loss during thawing. A rapid freezing promotes a large number of small ice crystals distributed uniformly throughout the tissue, both inside and outside the cells .Hence, products frozen with cryogenic technologies show a matrix of small ice crystals and a better texture than products frozen using slower heat transfer processes.
 
 
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