Coffee is the seed contained in a berry, the produce of a moderate sized tree called the Coffea Arabicum, and which has also been named Jasminum Ara-bicum. This tree grows erect, with a single stem, to the height of from eight to twelve feet, and has long, undivided, slender branches, bending downwards, these are furnished with evergreen leaves, not unlike those of the bay tree. The blossoms are white, sitting on short footstalks, and resembling a cherry, and having a pale, insipid, and somewhat glutinous pulp, inclosing two hard oval seeds, each about the size of an ordinary pea. One side of the seed is convex, while the other is fiat, and has a little straight furrow inscribed through its longest dimensions; while growing, the flat sides of the seed are towards each other. These seeds are immediately covered by a cartilaginous membrane, which has received the name of the parchment. The trees begin bearing when they are two years old; in their third year they are in full bearing. The aspect of a coffee plantation during the period of flowering, which does not last longer than one or two days, is very interesting.
In one night the blossoms expand themselves so profusely as to present the same appearance which has sometimes been witnessed in England when a casual snow-storm at the close of autumn has loaded the trees while still furnished with their full complement of foliage. The seeds are known to be ripe when the berries assume a dark red colour, and if then not gathered will drop from the trees. The planters in Arabia do not pluck the fruit, but place cloths for its reception beneath the trees, which they shake, and the ripened berries drop readily. These are afterwards spread upon mats, and exposed to the sun's rays until perfectly dry, when the husk is broken with large heavy rollers, made either of wood or stone. The coffee thus cleared of its husk is again dried thoroughly in the sun, that it may not be liable to heat when packed for shipment. The method employed in the West Indies differs from this. Negroes are set to gather such of the berries as are sufficiently ripe, and for this purpose are provided each with a canvass bag, having an iron ring or hoop at its mouth to keep it always distended, and this bag is slung round the neck so as to leave both hands at liberty. As often as this bag is filled, the contents are transferred to a large basket placed conveniently for the purpose.
It is the usual calculation, that each bushel of ripe berries will yield ten pounds' weight merchantable coffee. In curing coffee it is sometimes usual to expose the berries to the sun's rays, in layers five or six inches deep, on a platform. By this means the pulp ferments in a few days; and having thus thrown off a strong acidulous moisture, dries gradually during about three weeks: the husks are afterwards separated from the seeds in a mill. Other planters remove the pulp from the seeds as soon as the berries are gathered. The pulping-mill used for this purpose consists of a horizontal fluted roller, turned by a crank, and acting against a movable breast-board, so placed as to prevent the passage of whole berries between itself and the roller. The pulp is then separated from the seeds by washing them, and the latter are spread out in the sun to dry. It is then necessary to remove the membranous skin or parchment, which is effected by means of heavy rollers running in a trough wherein the seeds are put. This mill is worked by cattle. The seeds are afterwards winnowed to separate the chaff; and if any among them appear to have escaped the action of the roller, they are again passed through the mill.
The roasting of coffee for use is a process that requires some nicety; if burned, much of the fine aromatic flavour will be destroyed, and a disagreeable bitter taste substituted. The roasting is now usually performed in a cylindrical vessel, which is continually turned upon its axis over the fire-place, in order to prevent the too great heating of any one part, and to accomplish the continual shifting of the contents. Coffee should never be kept for any length of time after it has been roasted, and should never be ground until it is required for infusion, or some portion of its fine flavour will be dissipated. Count Rumford, who paid great attention to the management and preparation of coffee, used to preserve the aromatic fragrance of that which had been ground, by placing it into a cylindrical metallic box, which was covered by an accurately fitting piston in the inside, being well closed by a nicely adjusted cover on the outside. An improved apparatus for roasting coffee was patented by Mr. Evans in 1824, the operation of which, it is said, confers a flavour similar to that from Mocha to West India coffee; and, owing to the retention of the essential oil, a greater weight of roasted coffee is obtained from a given weight of the raw material. The art, according to Mr. Evans's practice, seems to consist in the abstraction of the aqueous and acidulous matter, without volatilizing the essential oil, upon which mainly depend the flavour and agreeable qualities of coffee. The apparatus consists of an elliptical iron retort, set in brick-work, over a furnace; the retort is made to revolve upon hollow axes, one of them serving as an exit passage for the vapour, which is delivered therefrom into a convoluted pipe, immersed in cold water, and is thereby condensed; the other hollow axis is for the convenience of introducing the " examiner," which is a perforated tube, used to draw out a sample of coffee under operation, while it serves also as a safety valve in case of the vapour accumulating in too great force. A series of the retorts are placed over their respective furnaces, and they are caused to revolve by geering connected to their axes, to which motion is given by a steam engine, or any other convenient power. When the roasting has been found complete, the retorts are lifted out of their apertures over the furnace, and turned over upon one of their axes, which is provided with an ingenious swivel bearing for that purpose; the coffee is then discharged, and the operation renewed upon a fresh quantity.
In the ordinary method of roasting coffee an acetic acid is generated, which is diffused in the liquor if the infusion remains long. To obviate this inconvenience, an apparatus was contrived called a biggin, in which the coffee is put into a bag suspended to the rim of the vessel, and boiling water having been poured through, it is separated and removed from the water, which remains pretty free from acid, and combined with much aromatic fragrance. In coffee roasted by Evans's distillatory process, before mentioned, the acetic acid is mainly got rid of, and therefore the same precautions that are used in the biggin are not necessary, and a richer infusion may be made by allowing the coffee to soak longer in the water; but as the fragrant principle is of a very volatile nature, Mr. Evans contrived the following apparatus, which is found to answer the objects intended extremely well, and will serve for the foundation of a machine of a more elegant exterior. The body a of the vessel is of a cylindrical form; it has a cover b at top, and at c a bottom, under which is a stand or furnace d containing a lamp e; at f is a floating piston with a hook underneath for suspending the ground coffee in a bag g.
The floating piston is made of two thin metal plates soldered together, with a hollow space between them capable of holding a sufficient quantity of air to render itself and the bag of coffee buoyant. The piston is accurately fitted to the cylinder, but so as to allow it to rise and fall freely with the surface of the liquid in which it floats, and thus preserve the infusion from the contact of air, and there is only an extremely fine circular line of liquor at the edges exposed; the heat and the aroma of the infusion is thus preserved until the last cup is drawn off. When coffee is ground to a fine powder, and placed loosely among the water, the particles are a long time subsiding, and are easily disturbed after having settled. To clear the liquid it has been usual to add a few shreds of isinglass or other animal gelatine. The inconvenience of this process probably caused the introduction of the bag, which is however not without some disadvantages; among which may be mentioned the trouble of cleansing, and the imperfect solution of a portion of the extractive matter when the coffee lies in so dense a mass.
It has accordingly been suggested to place the coffee between two flat perforated plates, at nearly the bottom of the vessel; the water should be supplied by a tube extending from the top of the vessel to the bottom, from whence it will ascend through the strainers, and the coffee contained between them, which being unconfined, every particle will be kept in agitation by the boiling water, and be thoroughly operated upon: to this arrangement the floating piston, before described, may be advantageously added.
Since the foregoing suggestions were made, Mr. Jones, of the Strand, has introduced a coffee-pot on the principle which is represented in the annexed cut. a is a vessel placed over a lamp furnace, into which the requisite quantity of water is put; b is a double vessel, the internal one consisting of a perforated metal cup to hold the ground coffee; c is another recipient fitting over b, and having a valve at d. When the water in a boils, the steam ascends amongst the coffee in b; and when the steam accumulates in sufficient force, its pressure upon the surface of the water in a causes the boiling fluid to ascend the pipe e e, and to be discharged into the vessel c; the lamp may then be blown out, and the liquid will percolate through the coffee in a, and the perforated strainer in its descent to the vessel a, which will thus become filled with a filtered and aromatic infusion.