Boiling hot water extracts from coffee, which has been properly roasted and ground, an aromatic substance of an exquisite flavour, together with a considerable quantity of astringent matter, of a bitter, but very agree able taste ; but this aromatic substance, which is sup posed to be an oil, is extremely volatile ; and is so feebly united to the water, that it escapes into the air with great facility.
If a cup of the very best coffee, prepared in the high est perfection, and boiling hot, be placed on a table in the middle of a room, and suffered to cool, it will, in cooling, fill the room with its fragrance ; but the coffee, after having become cold, will be found to have lost a great deal of its flavour. If it be again heated, its taste and flavour will be still farther impaired ; and after it has been heated and cooled two or three times, it will be found to be quite vapid and disgusting.
The fragrance diffused through the air is a proof, that the coffee has been deprived of its most volatile parts; and as that liquor is found to have lost its peculiar flavour, and also its exhilarating quality, it is inferred, that both these qualities must undoubtedly depend on the preser vation of those volatile parts which so readily escape.
If the liquid were perfectly at rest, the particles which could escape from its surface would be incomparably less in quantity than would escape by agitation, which would continually present new portions of the fluid to the air. But since all fluids, while heating or cooling, by partial communication, arc known to be agitated, the Count endeavours to chew by what means the heat of the liquor may be uniformly kept up in all its parts : for the consequence being, that the parts will, in those cir cumstances, be at rest, the motions by which the aro matic parts might have been dissipated, will not take place.
By pouring boiling water on the coffee, and surround ing the containing vessel with boiling water, or with the steam of boiling water, the coffee itself will be kept permanently at the same heat, and will not circulate, or be agitated.
The common method of boiling coffee in a coffee pot, is neither economical nor judicious. A large quantity of the material is wasted in this method, and more than half of the aromatic parts, so essential to its good quali ties, are lost.
One pound of good Mocha coffee, which, when pro perly roasted and ground, weighs only fourteen ounces.. will make, by proper management, fifty-six full cups of the very best coffee that can be made.
If it be not ground finely, the surfaces of the particles only will be acted upon by the hot water, and the waste will be very great, from the large proportion of coffee left in the grounds.
The size of a coffee cup in England usually answers to 83 cubic inches, but the Count considers the gill measure as a proper standard for a cup of coffee, which he therefore adopts. This will fill the former cup to seven eighths of its capacity, and a quarter of an ounce of ground coffee will be fully sufficient to make a gill of the most excellent coffee.
It is well known to chemists, that any solvent already in part charged with a substance intended to be taken up, will be less disposed than before to take up any ad ditional quantity ; and upon this is founded the process of percolation or straining, as is practised in brewing and other arts, and has been for some time recommended and used in making coffee. To this the Count gives his ap
probation. He finds, by experience, that the stratum of ground coffee to be laid upon a perforated metallic bot tom of a vessel or strainer, ought to be about two-thirds of an inch thick, and to be reduced by pressure by a pis ton or flat plate of metal (after levelling it) to less than half an inch. From the data he infers, by a chain of ob servations, that if the height of a cylindrical vessel or strainer be taken constantly at 5 inches, the diameter of its bottom must be—To make 1 cup of coffee = inch ; 2 cups =24 ; 3 or 4 cups= 24 ; 5 or 6 = ; 7 or = 4 ; 9 or 10 = 44 ; 11 or 12 = 5.
These strainers are to be suspended in their reservoirs or vessels for containing the coffee, and the whole in cluded in another vessel called the boiler, which is to contain boiling water kept hot by a lamp, or otherwise. One of the coffee pots recommended by the Count is a porcelain or earthen jug, with a tubular spout, not unlike those which we call milk jugs, except that these com monly have a lipspout (which would answer nearly as well.) Into the mouth of this is fitted a tin vessel, which fits and descends a little way down. It has a flat bottom perforated with many holes, and a good close cover ; and It would be well to have a round plate or rammer, to compress the coffee on itF bottom, and defend it from the stream of hot water, when poured in. These several parts are to be dipped in boiling water before using, and the difference between coffee made by this simple and cheap apparatus, of which the mug may also be applied to other uses, and that made by the most perfect machines, will scarcely be distinguishable." We shall now conclude this article with the following Table, shcwing the quantity of coffee exported at dif ferent times from Arabia, and the English, French, and Spanish colonies.
Humboldt computes, that the quantity of coffee an nually consumed in Europe is 53 millions of kilogram mes, or 116,971,000 pounds avoirdupois ;—that the con sumption of France is 230,000 quintals ; and that the consumption of Mexico, where the population is one fifth of that of France, is only 400 or 500 quintals.
For farther information on this subject, see Ellis's History of Coffee. Cadet de Vaux on the history and Properties of Coffee in the Journal de Physique,vol.lxiii. p. 216. Sept. 1806, or in Nicholson's Journal, vol. xvii. p. 118. Chenevix on a peculiar vegetable principle in Coffee, in Nicholson's Journal, vol. ii. p. 114. Raynal's History of European Settlements. Bruce's Travels. Edward's History of the West India Islands. Cordiner's Description of Ceylon, vol. i. p. 379. Valentia's Travels, vol. ii. p. 363. Stavorinus's Voyages, vol. iii. p. 328. Humboldt's Political essay on New Spain, vol. iii. p. 22. Count Rumford's 18th Essay; the article ARABIA, Vol. II. ; and the article COLONY. (w)