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Chocolate Liquor Pressing

Typically, the separation or pressing process begins by pumping hot chocolate liquor (200°C) into a horizontal hydraulic press with operating pressures of up to 550 bars. Screw presses or expellers are in limited use and are not discussed here in any detail. They are usually used to remove cocoa butter from whole beans and other cacao-containing materials. Both natural and alkalized chocolate liquors can be pressed to separate the cocoa butter from the solid cocoa cake. Pressing times are determined by the final fat content of cocoa cake, with 8.0% being the lowest practical value obtainable with the hydraulic press. Typically, a cycle time of 15 min is required to produce cocoa powder with fat content of 2224%. On the low end, 2530 min are required to reach a fat content of 1012%.

In the USA, cocoa powder is usually available in several fat content ranges including 2224%, 1618% and 1012%. Fat-free powders, which are now available, are possible by additional fat removal through application of critical fluid extraction or solvent extraction. The 1012% fat content powder is the most widely used for numerous reasons with economics probably being most important. Product developers should consider the higher fat content powders for the improved flavor they can contribute. If alkalized liquors are pressed the colors and flavors available increase and can best be described by evaluating various manufacturers' offerings. The cocoa cake formed from the pressing operation described above is then broken and milled to specified particle sizes as determined by end use.

Cocoa Grinding

Before grinding of this pressed cocoa cake can begin, it must go through a series of cooling steps. The hammer mill and disc mill are the more common mills being used by industry and a classifier is usually included as part of the system to improve grinding efficiency. In reality, the term grinding is misleading. The particle size of the finished powder is dependent upon particle size of the chocolate liquor pressed. Commonly used mills do not reduce the particle size of the cake; instead they tend to break up agglomerates. Figure 3.8 shows an example of a pulverizer used for this duty.

It must also be mentioned that cocoa powder must be tempered. This is a sort of controlled cooling operation during which the powder is held at specified temperatures for predetermined times to allow for the cocoa butter to form into a stable crystal configuration. The powder should then be stored properly if it is to maintain its color and remain soft and in a flowable state. Cocoa powder is susceptible to fat bloom as is found in chocolate. The powder will turn gray in color and will became rock hard if not tempered during the grinding process.

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