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Figure 6.4 Nibs, alkalizing, roasting and sterilizing process.
become detached from the beans. The nibs receive much less heating, although there is slight expansion which assists the detachment of the shell. The moisture content is reduced to 5-6%. Transfer of fat from nib to shell is less than in many conventional processes and the tendency of the nib to break up is also con- siderably reduced. This reduces the quantity of nib dust and mini- mizes loss during winnowing.
Following micronization the cocoa beans pass to winnowing machines ( see pages 272-3) where removal of the shell is com- pleted. The nibs are then roasted in a two-stage process designed to optimize product quality. A Tornado-type roaster is most com- monly used in the NARS process. This consists of an externally heated rotating drum in which nibs are heated by a combination of conduction and convection. In operation, the drum is charged with beans. Where alkalization is used (see pages 275-6) a pre-heated solution of alkali is sprayed onto the nibs before heating com- mences
The first stage of heating involves temperatures slightly below is 100°C and lasts for ca. 10 min. During this period the moisture content is reduced to 2-3%. The temperature is then raised for the second stage which lasts 15-20 min. The temperature used in the second stage can be as high as 130°C depending on the nature of the end product. The indirect heating used in Tornado-type dryers avoids case hardening of the nib surface, a problem with circulat- ing air dryers, and permits even drying and diffusion of moisture and and volatile compounds from the nib interior