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Heating zones

Cooling zones

Figure 2. Representation of flow of water and temperatures in a Cabinplant integrated blancher-cooler with heat exchanger.

Figure 2. Representation of flow of water and temperatures in a Cabinplant integrated blancher-cooler with heat exchanger.

A study of water heating by heat exchange (68% efficient) and by steam injection (17% efficient) confirmed the energy savings potential of heating by using a heat exchanger to minimize the escape of steam rather than by steam injection (4). Energy consumption can be reduced by minimizing the flow rate of water to the blancher (5), and a comparison of energy consumptions and effluent volumes of various water blanchers is shown in Table 2.

Loss of solubles may be reduced by maximizing product to water ratio, by recycling the blanch water, and by minimizing fresh water addition. This allows the solute concentration in the blanch water to rise toward that of the vegetable cell sap, the isotonic condition thus minimizing net solute loss (6). Tissue damage may promote more rapid loss of solutes and oxidative changes, for example, in peas (7), and hence mechanically induced product movement may be significant both to nutrient quality and product break-up of the more delicate vegetables such as broccoli. The Cabinplant integrated blancher-cooker (Denmark) utilizes minimal water volumes, heat exchangers, and a design to optimize many of the above points, and is the most sophisticated water blancher available (Fig. 2) (8).

One advantage of water blanching is that processing aids such as sodium chloride and sodium bicarbonate may be added to the blanch water to obtain the preferred quality of, for example, cabbage (9). However, blanch waters can also provide a good microbial growth medium. Total microbial loads may be reduced on heating by 104-105 per gram of product, but numbers of thermoduric organisms may not be reduced. It is therefore important that blanch-ers be easily accessible for cleaning, be constructed of stainless steel, and that dead spaces where food splashes may collect be designed out wherever possible.

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