Freezing, cooling and

In air freezing, freezing takes place in a cold current of air in differently arranged, usually continuously operated systems (tunnel, spiral band etc.). In the contact freezing processes used, the fish are pressed and frosted between two contact plates that are cooled by a flow of coolant. The blocks obtained by this process can be portioned into slabs or sticks using band saws. They can be sold to the consumer as such or breaded and prefried (170 °C, 20 s). Waste pieces (8-12%) are 

Product Moisture Protein Fat NaCP Edible portion  

Thawing is carried out in a stream of air saturated with water vapor at 20-25 °C or by spraying with water. Fish must be processed immediately after thawing because it loses juices rapidly and decays. Fish muscle enzymes have noticeable activity even at —10 °C. Excessively long storage or insufficient cooling, especially of fatty fish, results in a rancid off-flavor and an unattractive. 

Fish can be preserved by drying naturally in the sun or in drying installations. 

Stock fish, primarily nonfatty fish (cod, saithe, haddock, ling or tuck, which is often called cusk in North America) with head removed, split and gutted, is spread outdoors to dry in sea air (water content 12-18%). It is an unsalted fish product that is primarily produced in Norway and Iceland. Alternatively, machine-cut, headless and tailless fish which has been belly-clipped ( clipped fish) is salted, either directly or in brine, and then put through a drying process (salt content 18-20%, water content 40%). This is most often done with cod or other non-fatty fish species in Canada and Norway. 

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Cooling and freezing cannot improve a product, and the hest that can he achieved is to keep it near to the condition in which it entered the cooling process. This means that only the hest produce should he used, and this should he as fresh as possible. (This general principle must, of course, be interpreted in the light of local conditions and needs. In some countries of the world, preservation in cold stores is essential to prevent wastage, regardless of the quality of the crop.)... 

A different way obtaining short cooling and freezing times is to evaporate a part of the water in the product under vacuum. The evaporation energy of water at 0 °C is approximately 2.5 103 kJ/kg. To cool 1 kg of beef from 0 °C to -20 °C, 240 kJ have to be re-... 

Alvarez, M. D., Canet, W. (1997). Effect of pre-cooling and freezing rate on mechanical strength of potato tissues (cv Monalisa) at freezing temperatures. Z. Lebensm. Unters. Forsch. A., 205,282-289. 

The cooling and freezing of milk also cause shifts in the salts equilibria in milk, including changes in pH, as discussed in Chapters 2, 5 and 11. 

Hung. Yen-Con "Prediction of Cooling and Freezing Times/ Fond Technology. 137 tMay 1990). 

Willart, S., Sjostrom, G. 1966. The effect of cooling and freezing on the lipolysis in raw milk. Proc. 17th Int. Dairy Cong. (Munich) A, 287-295. 

Iron-chromium alloys, free from carbon, may be prepared from chromite by the alumino-thermic method. From a study of the cooling-and freezing-point curves it has been suggested that a compound, Cr Fe, exists, but this is questioned by Janecke, who studied the iron-chromium system by means of fusion curves and by the microscopic study of polished sections of various alloys between the limits 10 Fe 90 Cr and 90 Fe 10 Cr, and came to the conclusion that the system consists of a single eutectic which can form mixed crystals with either component. The eutectic contains 75 per cent, of chromium and melts at 1320° C. The addition of chromium to iron increases the readiness of attack by hydrochloric and sulphuric acids, but towards concentrated nitric acid the alloys are rendered passive. They remain bright in air and in water. The presence of carbon increases the resistance to acids and renders them very hard if carbon-free, they are softer than cast iron. All the alloys up to 80 per cent, chromium are magnetic. Molybdenum, titanium, vanadium, and tungsten improve the mechanical properties and increase the resistance to acids. 

The scheduling of the annealing protocol, including the notion of cooling and freezing cycles, was as before. The previous ratio of Ii to l2 of 2 and the optimal values of g 0.98-0.99 were found to be adequate. The value of Tq was a little lower at 20j.. 

The operations of mold and melt removal from the oven and melt transfer should be conducted as rapidly as possible to prevent premature cooling of the melt. Fluoroplastics have fairly high viscosity and require relatively long transfer time. To avoid premature cooling and freezing prior to the completion of transfer, mold temperature should be maintained at above the melting temperature of the polymer. 

Figure 5 pH changes during the cooling (and freezing) and rewarming of an ice-seeded citric acid-sodium phosphate buffer mixture, illustrating the effects of delayed crystallisation of sodium phosphate reproduced from Pikal (unpublished)... 

Traditionally the condenser cooling and freezing is achieved by direct expansion of frigorific fluids (HFCs allowed by the Montreal protocol), or nowadays liquid nitrogen (LN2), in the coils or the plates of the ice condenser. 

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