Page:Popular Science Monthly Volume 20.djvu/378

364 of common qualities is to be gained from the external aspect of the plants so brought into use. Between the leaf of the tea-plant and the long pod of the cacao-tree there is no visual resemblance to indicate a common constituent, or to suggest a parallel use. As unlike as their general appearance, even more diverse are the botanical characteristics of the caffeine-containing plants, representing, as they do, diverse families in the vegetable kingdom.

In the modes of preparation for use, the sources of caffeine present some coincidences, with many diversities. The coffee-berry, except in some Eastern countries, is roasted, an operation to which its valued fragrance is almost wholly due. The roasting develops from inodorous constituents a very diffusible empyreumatic oil of very appetizing odor. In the more elaborate preparation of the tea-leaf a degree of roasting appears to be always necessary for development of agreeable flavor, while a certain extent of fermentation precedes the roasting in the manufacture of black teas. For black tea the leaves are withered a little, rolled to liberate the juice, then left in balls for just enough fermentation, then sun-dried, and subjected to a careful firing in a furnace. For green teas the fresh leaves are first withered in hot pans, then rolled to liberate the juices, and slightly roasted in the pans, now sweated in bags, and returned to the pans for a final slow roasting, with stirring for eight or nine hours, beginning at the temperature of 160° Fahr. and falling to 120° at the close. These operations are here given as now conducted by the planters in India, and as proposed for tea-culture in the Southern United States, and are considerably abridged from the time-established routine of minute detail in China. The teas of commerce contain a distinct essential oil, a constituent which does more than all others to obtain the esteem and fix the value of each grade of tea in the market. The question of the effect of the curing process upon the essential oil—to liberate or generate or modify or dissipate it—is an inquiry of no little interest and consequence, and deserves more chemical investigation than it has received. In the manufacture of all the forms of chocolate, the cacao seeds, cleared of the shell-coat, are roasted to begin with. Without further treatment they constitute the "cacao-nibs." When ground, pressed to remove a part of the oil, made with sugar into a paste, flavored with vanilla, spices, etc., and cast in molds, we have "chocolate" proper. When left in the pulverulent form, or molded in porous and friable cakes, the article is presented as cacao or "cocoa," or "soluble cocoa"—the proportion of oil being diminished either by its removal under pressure, or by adding some form of starch or farina. "Flake cocoa" is made by crushing the roasted seed, shell and all. In the preparation of the South American maté, the leaves and twigs are subjected to a "curing" process, and roasted under a covering of earth to develop an aromatic principle which gives flavor to the beverage. The guarana, also, is dried or lightly roasted, though