[ TECHNOLOGY ] Technologies for industrial thawing
Thaw frozen fish faster and retain quality Thawing is an essential part of many industrial production processes. It affects both material yield and the quality of the final products and thus ultimately the efficiency of the entire process. As freezing is used more and more in the fish industry, the significance of the technical procedures required for industrial thawing (the reverse process) increases to the same extent.
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uring freezing, heat is removed from a product. To thaw the product again, the flow of energy has to be reversed, i.e. heat has to be put back into the product. The two are opposing processes and they differ in some details. Whereas during freezing the prime aim is to reach the target core temperature in the product as quickly as possible (“shock freezing”), a lot more factors have to be considered during thawing. This makes thawing the more sophisticated and more complex process, particularly with regard to the possible influence on, and the predictability of, the final results. Many of the problems that can occur during thawing are directly connected to heat transfer in frozen products. Heat transfer is a relatively slow process and the larger and thicker the product is, the more time it takes. It can be accelerated by increasing the thawing temperature, but that would also damage the product itself. The longer the thawing process lasts, the higher the risk that bacteria and microbes will develop and spread in the product. Longer thawing times also lead to more drip loss which changes the texture of the fish tissue. The media that are used to transfer heat to the product, such as air, water or steam, also play a role here. And under industrial conditions there www.eurofishmagazine.com
Thawing in still air is the simplest and cheapest way of defrosting products, but it is also among the slowest.
is often the additional problem of insufficient space for thawing and the fact that the process should not be too labour intensive. A number of other factors influence the thawing process, too: the composition of the frozen products, their water content, and the proportion of fat, protein and minerals they contain. It also makes a big difference whether the fish will be cooked and eaten immediately after thawing, or whether it is to undergo
processing to a convenience product with a correspondingly long shelf-life that will be eaten later. Already the time required to thaw frozen products often proves to be a bottleneck which can slow down the production processes of manufacturing companies or even bring them to a halt. If, for example, raw material was not thawed in time or not in the quantities needed for subsequent processing stages it is hardly possible to supply the missing quan-
tities in a short time. To shorten the defrosting time, it is common in many companies to temper some of the ingredients to have them “on hold” for production. During tempering, the core temperature of -18°C, which is normal for frozen products is raised to about -10°C. The product is still frozen, but it can be stored for about a day in the refrigerator and then be thawed as required in a much shorter time. With every degree that the temperature rises, however, the risk of premature
Eurofish Magazine 4 / 2013
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