The quantity of ground coffee for one full cup, should not be less than 108 grains troy, which is rather less than a quarter of an ounce. This coffee, when made, fills a coffee-cup of the common size quite full.
In making coffee, several circumstances must be carefully attended to: in the first place, the coffee must be ground fine, otherwise the hot water will not have time to penetrate to the centres of the particles; it will merely soften them at their surfaces, and passing rapidly between them, will carry away but a small part of those aromatic and astringent substances on which the goodness of the liquor entirely depends. In this case the grounds of the coffee are more valuable than the insipid wash which has been hurried through them, and afterwards served up under the name of coffee.
Formerly, the ground coffee being put into a coffee-pot, with a sufficient quantity of water, the coffee-pot was put over the fire, and after the water had been made to boil a certain time, the pot was removed from the fire, and the grounds having had time to settle, or having been fined down with isinglass, the clear liquor was poured off, and immediately served up in cups. This was a bad practice of making coffee.
From the results of several experiments made by Count Rumford, to ascertain what proportion of the aromatic and volatile particles in the coffee escape, and are left in this process, he found that it amounted to considerably more than half.
When coffee is made in the most advantageous manner, the ground coffee is pressed down in a cylindrical vessel a, ([fig. 4], plate facing the title page), which has its bottom pierced with many small holes, so as to form a metal strainer; a proper quantity of boiling hot water being poured cautiously on this layer of coffee in powder, the water penetrates it by degrees, and after a certain time begins to filter through it. This gradual percolation brings continually a succession of fresh particles of hot water into contact with the ground coffee; and when the last portion of the water has passed through it, every thing capable of being dissolved by the water will be found to be so completely washed out of it, that what remains will be of no kind of value.
It is, however, necessary to the complete success of this operation, that the coffee should be ground to a powder sufficiently fine. In order that the coffee may be perfectly good, the stratum of ground coffee, on which the boiling water is poured, must be of a certain thickness, and it must be pressed together with a certain degree of force, by means of the presses b, ([fig. 4].) If it be too thin, or not sufficiently pressed together, the water will pass through it too rapidly; and if the layer of ground coffee be too thick, or if it be too much pressed together, the water will be too long in passing through it, and the taste of the coffee will be injured.
Count Rumford recommends, as of importance, that the surface of the coffee be rendered quite level after it is put into the strainer before any attempt is made to press it together, that the water, in percolating, may act equally on every part.
When the coffee is made, the strainer, or cylindrical vessel a is removed, and the lid of it is made to serve as the lid for the coffee pot.
The following table shews the diameters and heights of the cylindrical vessels, or strainers, to be used in making the following quantities of coffee:—
| Quantity of Coffee to be made at once. | Diameter of the Strainer. | Height of the Strainer. | ||
|---|---|---|---|---|
| In Inches. | In Inches. | |||
| 1 cup | 1 | 1⁄2 | 5 | 1⁄4 |
| 2 cups | 2 | 1⁄8 | 5 | 1⁄4 |
| 3 or 4 cups | 2 | 3⁄4 | 5 | |
| 5 or 6 cups | 3 | 1⁄2 | 5 | 1⁄8 |
| 7 or 8 cups | 4 | 5 | 1⁄4 | |
| 9 or 10 cups | 4 | 5⁄8 | 5 | 1⁄3 |
| 11 or 12 cups | 5 | 5 | 1⁄2 | |