The mixture is now passed through a mill, which has been described as looking like a multiple mangle. The object of this is to break down the sugar and cacao to smaller particles. The rolls may be made either of granite (more strictly speaking, of quartz diorite) or of polished chilled cast iron. Chilled cast iron rolls have the advantage that they can be kept cool by having water flowing through them. A skilled operator is required to set the rolls in order that they may give a large and satisfactory output. The cylinders in contact run at different speeds, and, as will be seen in the diagram, the chocolate always clings to the roll which is revolving with the greater velocity, and is delivered from the rolls either as a curtain of chocolate or as a spray of chocolate powder. It is very striking to see the soft chocolate-coloured dough become, after merely passing between the rolls, a dry powder—the explanation is that the sugar having been more finely crushed now requires a greater quantity of cacao butter to lubricate it before the mixture can again become plastic. The chocolate in its various stages of manufacture, should be kept warm or it will solidify and much time and heat (and possibly temper) will be absorbed in remelting it; for this and other reasons most chocolate factories have a number of hot rooms, in which the chocolate is stored whilst waiting to pass on to the next operation. The dry powder coming from the rolls is either taken to a hot room, or at once mixed in a warm mélangeur, where curiously enough the whole becomes once again of the consistency of dough. The grinding between the rolls and the mixing in the mélangeur are repeated any number of times until the chocolate is of the desired fineness. Whilst there are a few people who like the clean, hard feel of sugar crystals between the teeth, the present-day taste is all for very smooth and highly refined chocolate; hence the grinding operation is one of the most important in the factory, and is checked at the works at Bournville by measuring with a microscope the size of the particles. The cost of fine grinding is considerable, for whilst the first breaking down of the cacao nibs and sugar crystals is comparatively easy, it is found that as the particles of chocolate get finer the cost of further reduction increases by leaps and bounds. The chocolate may now proceed direct to the moulding rooms or it may first be conched.
SECTION THROUGH CHOCOLATE GRINDING ROLLS.
(d) Conching.
We now come to an extraordinary process which is said to have been originally introduced to satisfy a fastidious taste that demanded a chocolate which readily melted in the mouth and yet had not the cloying effect which is produced by excess of cacao butter. In this process the chocolate is put in a vessel shaped something like a shell (hence called a conche), and a heavy roller is pushed to and fro in the chocolate. Although the conche is considered to have revolutionized the chocolate industry, it will remain to the uninitiated a curious sight to see a room full of machines engaged in pummelling chocolate day and night. There is no general agreement as to exactly how the conche produces its effects—from the scientific point of view the changes are complex and elusive, and too technical to explain here—but it is well known that if this process is continued for periods varying according to the result desired from a few hours to a week, characteristic changes occur which make the chocolate a more mellow and finished confection, having more or less the velvet feel of chocolat fondant.
"CONCHE" MACHINES.
Reproduced by permission of Messrs. J. Baker & Sons, Willesden.