The Aromatic Principles of Coffee

To ascertain just what substance or substances give the pleasing and characteristic aroma to coffee has long been the great desire of both practical and scientific men interested in the coffee business. This elusive material has been variously called caffeol, caffeone, "the essential oil of coffee," etc., the terms having acquired an ambiguous and incorrect significance.

"This fragrance of coffee is certainly owing to the escape of a volatile aromatic substance which did not originally exist as such in the grain, but which is formed in the process of roasting it." Comparison of the aroma given off by coffee during the roasting process with that of fresh-ground roasted coffee shows that the two aromas, although somewhat different, may be attributed to the same substances present in different proportions in the two cases.

Bernheimer reported water, caffein, caffeol, acetic acid, quinol, methylamin, acetone, fatty acids and pyrrol in the distillate coming from roasting coffee. Jaeckle examined a similar product and found considerable quantities of caffein, furfurol, and acetic acid, together with small amounts of acetone, ammonia, trimethylamin, and formic acid. By distilling roasted coffee with superheated steam, Erdmann obtained an oil consisting of an indifferent portion of 58 percent and an acid portion of 42 percent, consisting mainly of a valeric acid, probably alphamethylbutyric acid.

The fraction containing the characteristic odorous constituent of coffee boiled at 93° C. under 13 mm. pressure. The yield of this latter principle was extremely small, only about 0.89 gram being procured from 65 kilos of coffee. Pyridin was also shown to be present in coffee by Betrand and Weisweiller and by Sayre. As high as 200 to 500 milligrams of this toxic compound have been obtained from 1 kilogram of freshly roasted coffee. As stated above, the empyreumatic volatile aromatic constituents of the coffee are without question formed during and by the roasting process.

According to Thorpe, the most favorable temperature for development of coffee odor and flavor is about 200° C. Erdmann claimed to have produced caffeol by gently heating together caffetannic acid, caffein, and cane sugar. By means of careful work, Grafe came closer to ascertaining the origin of the fugacious aromatic materials. His work with normal, caffein-free coffee and with Thum's purified coffee led him to state that a part of these substances was derived from the crude fiber, probably from the hemi-cellulose of the thick endosperm cells.

The products of roasting inter-react to produce many compounds of varying degrees of complexity and toxicity. The great difficulty 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.

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