ifficulty which arises in the attempt to identify the
aromatic constituents of coffee is that the caffeols of no two coffees
may be said to be the same. The reason for this is apparent; for the
green coffees themselves vary in composition, and those of the same
constitution are not roasted under identical conditions. Therefore, it
is not to be expected that the decomposition products formed by the
action of the different greens would be the same. Also, these volatile
products occur in the roasted coffee in such a small amount that the
ascertaining of their percentage relationship and the recognition of all
that are present are not possible with the methods of analysis at
present at our disposal. Until better analytical procedures have been
developed we can not hope to establish a chemical basis for the grading
of coffees from this standpoint.

_Coffee Oil and Fat_

It is well to distinguish between the "coffee oils," as they are termed
by the trade, and true coffee oil. In speaking of the qualities of
coffee, connoisseurs frequently use erroneous terms, particularly when
they designate certain of the flavoring and aromatic constituents of
coffee as "oils" or "essential oils." Coffee does not contain any
essential oils, the aromatic constituent corresponding to essential oil
in coffee being caffeol, a complex which is water-soluble, a property
not possessed by any true oil. True, the oil when isolated from roasted
coffee does possess, before purification, considerable of the aromatic
and flavoring constituents of coffee. They are, however, no part of the
coffee fat, but are held in it no doubt by an enfleurage action in much
the same way that perfumes of roses, etc., are absorbed and retained by
fats and oils in the commercial preparation of pomades and perfumes.
This affinity of the coffee oil for caffeol assists in the retention of
aromatic substances by the whole roasted bean. However, upon extraction
of ground roasted coffee with water, the caffeol shows a preferential
solubility in water, and is dissolved out from the oil, going into the
brew.

The true oil of coffee has been investigated to a fair degree and has
been found to be inodorous when purified. Analysis of green and roasted
coffees shows them to possess between 12 percent and 20 percent fat.
Warnier[155] extracted ground unroasted coffee with petroleum ether,
washed the extract with water, and distilled off the solvent, obtaining
a yellow-brownish oil