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.]

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 v