Blanching Methods Water Blanching

Water blanching is the most widely used method. There are four basic designs of water blancher.

1. The tubular blancher in which particulate vegetable matter is transported by pumped water through a system of tubes for the required residence time. Direct steam injection is used to heat the water to blanch temperature, while tube length and product flow rate govern the blanch time.

2. The rotary screw blancher in which a central screw rotates, at a speed that moves the product forward to give the required blanch time, within a static drum containing the blanch water.

3. The rotary blancher, which comprises a drum with a scroll attached to the inner wall, rotating on trunnions.

4. The thermascrew blancher in which the rotating central screw is hollow and contains the heating medium.

Other designs have been developed for various products, such as the countercurrent blanching tower in which product and hot water are moved in opposite directions to promote rapid heat transfer. Product characteristics vary considerably and types (b) and (c) have been used widely. For rotary water blanchers, by a relatively simple scale-up of the basic design, ie, increasing blancher length, blancher capacity is increased for a range of blanch times. Estimates of product outputs can be predicted from data based on trials, as shown by the example in Figure 1 and Table 1.

Capital and running costs are relatively low for water blanchers, and thermal efficiency has been reported to be as high as 60% (2). Improvements in design have been directed at reducing energy and water consumption to minimize leaching and effluent. Mean heat utilization for a blancher with an average spinach capacity of 58,000 kg/h has been estimated at 39%, assuming a value of 758 kJ/kg for raw spinach leaves free from adhering water (3). Energy consumptions of a tubular water blancher and a water blancher with a screw conveyor have been measured as a basis for suggesting energy conserving modifications. The former required 0.54 MJ/kg and the latter 0.91 MJ/kg, indicating the importance of complete steam condensation.

Figure 1. Typical example of relation between product output and blanch time for various products blanched in various sizes of rotary water blancher. For a blancher diameter = 2 m, blancher length is approximately a = 3.1 m, b = 4.5 m, c = 5.9 m, d = 7.4 m, and e = 8.8 m.

Table 1. Multiply Graph Outputs by Appropriate Factor for These Products

Product Factor

Potatoes

Table 1. Multiply Graph Outputs by Appropriate Factor for These Products

Product Factor

Potatoes

whole

Homemade Pet Food Secrets

Homemade Pet Food Secrets

It is a well known fact that homemade food is always a healthier option for pets when compared to the market packed food. The increasing hazards to the health of the pets have made pet owners stick to containment of commercial pet food. The basic fundamentals of health for human beings are applicable for pets also.

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