As all cacao is liable to contain a little free shell, dried pulp (often taken for twigs), threads of sacking and other foreign matter, it is very carefully sieved and sorted before passing on to the roasting shop. In this process curios are occasionally separated, such as palm kernels, cowrie shells, shea butter nuts, good luck seeds and "crab's eyes." The essential part of one type of machine (_see illustration_) which accomplishes this sorting is an inclined revolving cylinder of wire gauze along which the beans pass. The cylinder forms a continuous set of sieves of different sized mesh, one sieve allowing only sand to pass, another only very small beans or fragments of beans, and finally one holding back anything larger than single beans (_e.g._, "cobs," that is, a collection of two or more beans stuck together). [Illustration: CACAO BEAN SORTING AND CLEANING MACHINE. Reproduced by permission of Messrs. J. Baker & Sons, Ltd., Willesden.] Another type of cleaning machine is illustrated by the diagram on the opposite page. This machine with its shaking sieves and blast of air makes a great clatter and fuss. It produces, however, what the manufacturers desire--a clean bean sorted to size. [Illustration: DIAGRAM OF CACAO BEAN CLEANING MACHINE. This is a box fitted with shaking sieves down which the cacao beans pass in a current of air. Having come over some large and very powerful magnets, which take out any nails or fragments of iron, they fall on to a sieve (1/4-inch holes) which the engineer describes as "rapidly reciprocating and arranged on a slight incline and mounted on spring bars." This allows grit to pass through. The beans then roll down a plane on to a sieve (3/8-inch holes) which separates the broken beans, and finally on to a sieve with oblong holes which allows the beans to fall through whilst retaining the clusters. The beans encounter a strong blast of air which brushes from them any shell or dust clinging to them.] (_c_) _Roasting the Beans._ As with coffee so with cacao, the characteristic flavour and aroma are only developed on roasting. Messrs. Bainbridge and Davies (chemists to Messrs. Rowntree) have shown that the aroma of cacao is chiefly due to an amazingly minute quantity (0.0006 per cent.) of linalool, a colourless liquid with a powerful fragrant odour, a modification of which occurs in bergamot, coriander and lavender. Everyone notices the aromatic odour which permeates the atmosphere round a chocolate factory. This odour is a bye-product of the roasting shop; possibly some day an enterprising chemist will prevent its escape or capture it, and sell it in bottles for flavouring confectionery, but for the present it serves only to announce in an appetising way the presence of a cocoa or chocolate works. [Illustration: SECTION THROUGH GAS HEATED CACAO ROASTER.]