All of the different varieties or kinds of coffee found upon the market are from two species of _Coffea_; namely, _C. Arabica_ and _C. Liberica_; the latter yielding the Liberian coffee, which is of excellent quality.
There are a number of so-called coffees which are used as substitutes for true coffee, of which the following are the more important. California coffee is the somewhat coffee-like fruit of _Rhamnus Californica_. Crust coffee is a drink resembling coffee in color, made from roasted bread crusts steeped in water. Mogdad or Negro coffee is the roasted seeds of _Cassia occidentalis_, which are used as a substitute for coffee, though they contain no caffeine. Swedish coffee is the seeds of _Astragalus Boeticus_ used as coffee, for which purpose it is cultivated in parts of Germany and Hungary. Wild coffee is a name given to several plants native in India, as _Faramea odoratissima_, _Eugenia disticha_, and _Casearia laetioides_. Kentucky coffee is a large leguminous tree (_Gymnocladus Canadensis_) of which the seeds (coffee nut) are used as a substitute for coffee.
The coffee beans are roasted before they are in suitable condition for use. At first the green beans were used. According to one story, a shepherd noticed that some of his sheep ate the fruit of the coffee tree, and, as a result, became very frisky. Presuming that the coffee beans were the cause, he also ate of the beans and noted an exhilarating effect. The use of the roasted beans was said to have originated in Holland. Roasting should be done carefully in a closed vessel in order to retain as much of the aroma as possible. This process modifies the beans very much; they change from green or greenish to brown and dark brown and become brittle; they lose about 15 to 30 per cent. of their weight, at the same time increasing in size from 30 to 50 per cent. The aroma is almost wholly produced by the roasting process, but if continued too long or done at too high a temperature the aroma is again lost. The temperature should be uniform and the beans should be stirred continually. It should also be remembered that not all kinds or grades of coffee should be roasted alike. In order to develop the highest aroma, Mocha coffee should be roasted until it becomes a reddish yellow, and has lost 15 per cent of its weight. Martinique coffee should be roasted to a chestnut brown, with a loss of 20 percent in weight; Bourbon to a light bronze and a loss in weight of 18 percent.