The diagram and photo show one of the types of roasting machines used at Bournville. It resembles an ordinary coffee roaster, the beans being fed in through a hopper and heated by gas in the slowly revolving cylinder. The beans can be heard lightly tumbling one over the other, and the aroma round the roaster increases in fullness as they get hotter and hotter. The temperature which the beans reach in ordinary roasting is not very high, varying round 135° C. (275° F), and the average period of roasting is about one hour. The amount of loss of weight on roasting is considerable (some seven or eight per cent.), and varies with the amount of moisture present in the raw beans.
There have been attempts to replace the æsthetic judgment of man, as to the point at which to stop roasting, by scientific machinery. One rather interesting machine was so devised that the cacao roasting drum was fitted with a sort of steelyard, and this, when the loss of weight due to roasting had reached a certain amount, swung over and rang a bell, indicating dramatically that the roasting was finished. As beans vary amongst other things in the percentage of moisture which they contain, the machine has not replaced the experienced operator. He takes samples from the drum from time to time, and when the aroma has the character desired, the beans are rapidly discharged into a trolley with a perforated bottom, which is brought over a cold current of air. The object of this refinement is to stop the roasting instantly and prevent even a suspicion of burning.
After roasting, the shell is brittle and quite free from the cotyledons or kernel. The kernel has become glossy and friable and chocolate brown in colour, and it crushes readily between the fingers into small angular fragments (the "nibs" of commerce), giving off during the breaking down a rich warm odour of chocolate.
(d) Removing the Shells.
It has been stated (see Fatty Foods, by Revis and Bolton) that it was formerly the practice not to remove the shell. This is incorrect, the more usual practice from the earliest times has been to remove the shells, though not so completely as they are removed by the efficient machinery of to-day.
CACAO BEAN, SHELL AND GERM.
In A Curious Treatise on the Nature and Quality of Chocolate, by Antonio Colmenero de Ledesma (1685), we read: "And if you peel the cacao, and take it out of its little shell, the drink thereof will be more dainty and delicious." Willoughby, in his Travels in Spain, (1664), writes: "They first toast the berries to get off the husk," and R. Brookes, in the Natural History of Chocolate (1730), says: "The Indians ... roast the kernels in earthen pots, then free them from their skins, and afterwards crush and grind them between two stones."
He further definitely recommends that the beans "be roasted enough to have their skins come off easily, which should be done one by one, laying them apart ... for these skins being left among the chocolate, will not dissolve in any liquor, nor even in the stomach, and fall to the bottom of the chocolate-cups as if the kernels had not been cleaned."