Roasting is a delicate operation requiring experience and discretion. Even in these days of scientific management it remains as much an art as a science. It is conducted in revolving drums to ensure constant agitation, the drums being heated either over coke fires or by gas. Less frequently the heating is effected by a hot blast of air or by having inside the drum a number of pipes containing super-heated steam. [Illustration: ROASTING CACAO BEANS. (Messrs. Cadbury Bros'. Works, Bournville).] 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 deg. C. (275 deg. 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 aesthetic 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. [Illustration: CACAO BEAN, SHELL AND GERM.]