Count Rumford (Benjamin Thompson)
“Of the Excellent Qualities of Coffee
and the Art of Making it in the Highest Perfection” [*]
The use of science is so to explain the operations which take place in the practice of the arts, and to discover the means of improving them; and there is no process, however simple it may appear to be, that does not afford an ample field for curious and interesting investigation.
As those domestic arts and elegant refinements which the progress of industry and the increase of wealth and knowledge introduce in society contribute to the comfort and happiness of great numbers of respectable individuals, their improvement must be interesting to all those who take pleasure in contemplating the prosperity of mankind and in contributing to their innocent enjoyments.
Among the numerous luxuries of the table unknown to our forefathers, which have been imported into Europe in modern times, coffee may be considered as one of the most valuable.
Its taste is very agreeable, and its flavour uncommonly so; but its principal excellence depends on its salubrity and on its exhilarating quality.
It excites cheerfulness without intoxication, and the pleasing flow of spirits which it occasions lasts many hours, and is never followed by sadness, languor, or debility.
It diffuses over the whole frame a glow of health, and a sense of ease and well-being which is exceedingly delightful. Existence is felt to be a positive enjoyment, and the mental powers are awakened and rendered uncommonly active.
It has been facetiously observed that there is more wit in Europe since the use of coffee has become general among us; and I do not hesitate to confess that I am seriously of that opinion.
Some of the ablest, most brilliant, and most indefatigable men I have been acquainted with have been remarkable for their fondness for coffee; and I am so persuaded of its powerful effects in clearing up the mind and invigorating its faculties that on very interesting occasions I have several times taken an additional dose of it for that very purpose.
That coffee has greatly contributed to our innocent enjoyments, cannot be doubted; and experience has abundantly proved that so far from being unwholesome it is really very salubrious.
This delicious beverage has so often been celebrated, both in prose and verse, that it does not stand in need of my praises to recommend it. I shall therefore confine myself to the humble office of showing how it can be prepared in the greatest perfection.
There is no culinary process that is liable to so much uncertainty in its results as the making of coffee; and there is certainly none in which any small variation in the mode of operation produces more sensible effects.
With the same materials, and even when used in the same proportions, this liquor is one day good and the next bad, and nobody perhaps can even guess at the cause of this difference; and what renders these variations of greater importance is this remarkable circumstance, that when coffee is bad, when it has lost its peculiar aromatic flavour which renders it so very agreeable to the organs of taste and of smell, it has lost its exhilarating qualities, and with them all that was valuable in it.
Different methods have been employed in making coffee, but the preparation of the grain is nearly the same in all of them. It is first roasted in an iron pan, or in a hollow cylinder made of sheet iron, over a brisk fire; and when from the colour of the grain and the peculiar fragrance which it acquires in this process it is judged to be sufficiently roasted, it is taken from the fire and suffered to cool. When cold, it is pounded in a mortar, or ground in a handmill to a coarse powder, and preserved for use.
[Excursus on roasting and storing coffee.]
Before I proceed to describe the apparatus I shall recommend for making coffee, it will be useful to inquire what the causes are which render the preparation of that liquor so precarious; and, in order to facilitate that investigation, we must see what the circumstances are on which the qualities depend which are most esteemed in coffee.
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 agreeable taste; but this aromatic substance, which is supposed to be an oil, is extremely volatile, and is so feebly united to the water that it escapes from it into the air with great facility.
If a cup of the very best coffee prepared in the highest perfection, and boiling hot, be placed on a table in the middle of a large 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 sure indication that the coffee has lost some of its most volatile parts; and as that liquor is found to have lost its peculiar flavour, and also its exhilarating quality, there can be no doubt but that both these depend on the preservation of those volatile particles which escape into the air with such facility.
[Excursus on preserving flavor.]
In order that coffee may retain all those aromatic particles which give to that beverage its excellent qualities, nothing more is necessary than to prevent all internal motions among the particles of that liquid, by preventing its being exposed to any change of temperature, either during the time employed in preparing it, or afterwards till it is served up.
This may be done by pouring boiling water on the coffee in powder, and surrounding the machine in which the coffee is made by boiling water or by the steam of boiling water; for the temperature of boiling water is invariable (while the pressure of the atmosphere remains the same), and the temperature of steam is the same as that of the boiling water from which it escapes.
But the temperature of boiling water is preferable to all others for making coffee, not only on account of its constancy, but also on account of its being most favourable to the extraction of all that is valuable in the roasted grain.
[Comments on water temperature.]
Nobody, I fancy, can be fonder of coffee than I am. I have regularly taken it twice a day for many years; and I certainly take care to have the very best that can be procured, and no expense is spared in making it good.
The reader will no doubt be surprised when I assure him that one pound avoirdupois of good Mocha coffee, which, when properly roasted and ground, weighs only fourteen ounces, serves for making fifty-six full cups of the very best coffee (in my opinion) that can be made.
The quantity of ground coffee which I use for one full cup is 108 grains Troy, which is rather less than a quarter of an ounce. This coffee when made would fill a coffee-cup of the common size quite full; but I use a larger cup, into which the coffee being poured boiling hot, on a sufficient quantity of sugar (half an ounce), I pour into it about one-third of its volume of good sweet cream, quite cold. On stirring these liquids together, the coffee is suddenly cooled, and in such a manner as not to be exposed to the loss of any considerable portion of its aromatic particles in that process.
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.
This secret has been but too well known to some servants abroad, where coffee is more generally used than in England, and where the preparation of it has not been controlled by the laws. When complaints are made that the coffee is too weak, they are never at a loss for a remedy for that evil; and when it has once been established, as a rule in the family, that one ounce of ground coffee is indispensably necessary to make a cup of good strong coffee, their point is gained.
But before we can determine with certainty how much ground coffee is necessary in order to make a cup of good coffee, we must ascertain the contents of a coffee-cup; and as the sizes of coffee-cups are very different in different countries, and even vary considerably in the same country, we must begin by adopting some certain size to serve as a standard.
[Excursus on cup size and brew strength.]
It is well known to chemists that any solid substance which is soluble in any liquid menstruum is dissolved with greater difficulty or more slowly as the liquid is more charged with that substance.
Now, when coffee is made in the most advantageous manner, the ground coffee is pressed down in a cylindrical vessel which has its bottom pierced with many small holes so as to form a strainer, and 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 pure 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, as has already been observed.
This method of making coffee, by percolation, has been practised many years, and its usefulness is now universally acknowledged. I do not know who was the first to propose it, but being thoroughly persuaded of the merit of the contrivance I have been desirous of recommending it; and I conceived that the most effectual way of recommending it would be to explain the mechanical and chemical principles on which its superiority depends.
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. 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.
Another circumstance, to which little attention has hitherto been paid, but which I have found to be of considerable importance, is the levelling of the surface of the ground coffee after it has been put into the strainer, before any attempt is made to press it together.
When the ground coffee is poured into the strainer, it always stands much higher in one part of this vessel than elsewhere; and, if in that situation it be pressed down on the perforated bottom of this vessel without being previously levelled, it will be much more pressed in some parts than in others; and, as the water will not fail to pass most rapidly where it meets with the least resistance, a considerable portion of the ground coffee will be so crowded together as to prevent the water from passing through it, and consequently will contribute little or nothing to the strength of the beverage.
To remedy this inconvenience, I use the following simple contrivance. The circular plate of tin, with a rod fastened to its centre which serves as a rammer for pressing down the ground coffee, has four small projecting square bars of about one tenth of an inch in width fastened to the under side of it, and extending from the circumference of the plate to within about one quarter of an inch of its centre.
On turning this plate round its axis, by means of the rod which serves as a handle to it (the rod being made to occupy the axis of the cylindrical vessel), the projecting bars are made to level the ground coffee; and after this has been done, and not before, the coffee is pressed together.
This circular plate is pierced by a great number of small holes which permit the water to pass through it, and it remains in the cylindrical vessel during the whole of the time that the coffee is making. It reposes on the surface of the ground coffee, and prevents its being thrown out of its place by the water which is poured on it.
The rod which serves as a handle to this circular plate is so short that it does not prevent the cover of the cylindrical vessel from being put down into its place.
After having made a great number of experiments in order to determine what thickness is best for the layer of ground coffee, I have found that two thirds of an inch answers best for the coffee in powder before it is pressed together, and that it ought to be so pressed as to be reduced to the thickness of something less than half an inch.
And as the quantity of ground coffee necessary for making a cup of good coffee (a quarter of an ounce avoirdupois) just fills a cylindrical measure which is 1.15 inches in diameter and in height, its volume amounts to 1.1945 cubic inches; consequently a cylindrical vessel (which I shall call the strainer) proper for making one cup of coffee must be of such diameter that 1.1945 cubic inches of ground coffee will fill it to the height of two thirds of an inch.
On making the computation, it will be found that one inch and a half is the most proper diameter for the strainer to be employed in making one single cup of good coffee. And as the thickness of the stratum of ground coffee must always be the same, whatever may be the number of cups that are made at the same lime, the diameter of strainers of different sizes will be as follows, viz.: —
[Table of number of cups to height in inches.]
For common use the following sizes will answer very well; and, in order that workmen may not have the trouble of computing the heights of the cylindrical vessels which I have called strainers, which contain the water that is poured on the ground coffee, I have given these heights in the following table. They have been determined on the supposition that the diameter of the vessel is always just equal to the diameter of the perforated bottom by which it is closed below, and that the quantity of water necessary for making one cup of coffee is 8 1/3 cubic inches.
A Table, showing the Diameters and Heights of the cylindrical Vessels (or Strainers) to be used in making the following Quantities of Coffee : —
[Table]
As there is so little difference in the heights of these strainers, and as a small additional height will be rather advantageous than otherwise, I would recommend them to be made all of the same height; viz., 5 1/2 inches in height.
As these strainers must be suspended in their reservoirs which are destined for receiving the coffee, and at such a height that after all the coffee has passed through the strainer the bottom of the strainer may still be above the surface of the coffee in the reservoir, it will be best to make the reservoir of a conical form, and just large enough above to receive the strainer in such a manner that it may be suspended in the reservoir by means of a narrow projecting brim.
The boiler in which the reservoir is suspended may likewise be made conical, and of such diameter above as to receive the reservoir in such a manner as to be firmly united to it.
The reservoir and its boiler must be soldered together above at their brims, and the reservoir must be suspended in its boiler in such a manner that its bottom may be about a quarter of an inch above the bottom of the boiler.
The small quantity of water which it will be necessary to put into the boiler, in order that the reservoir for the coffee may be surrounded by steam, may be introduced by means of a small opening on one side of the boiler, situated above and near the upper part of its handle.
The spout through which the coffee is poured out passes through the side of the boiler, and is fixed to it by soldering. The cover of the boiler serves at the same time as a cover for the reservoir and for the cylindrical strainer; and it is made double, in order more effectually to confine the heat.
The boiler is fixed below to a hoop, made of sheet brass, which is pierced with many holes. This hoop, which is one inch in width, and which is firmly fixed to the boiler, serves as a foot to it when it is set down on a table; and it supports it in such a manner that the bottom of the boiler is elevated to the height of half an inch above the table.
When the boiler is heated over a spirit lamp, or over a small portable furnace in which charcoal is burned, as the vapour from the fire will pass off through the holes made in the sides of the hoop, the bottom of the hoop will always remain quite clean, and the table-cloth will not be in danger of being soiled when this coffee-pot is set down on the table.
As the hoop is in contact with the boiler, in which there will always be some water, it will be so cooled by this water as never to become hot enough to burn the table-cloth.
The bottom of the boiler may be cleaned occasionally on the under side with a brush or a towel, but it should not be made bright; for when it is bright it will be more difficult to heat the water in it than when it is tarnished and of a dark brown color.
But the sides of the boiler should be kept as bright as possible; for, when its external surface is kept clean and bright, the boiler will be less cooled by the surrounding cold bodies than when its metallic splendour is impaired by neglecting to clean it.
As the small quantity of water which is put into the boiler serves merely for generating the steam which is necessary in order to keep the reservoir and its contents constantly boiling hot, if the reservoir be made of silver or even of common tin, the boiler may without the smallest danger be made of copper, or of copper plated with silver, which will give to the boiler an elegant appearance, and at the same time render it easy to keep it clean on the outside.
The boiler may likewise be made of tin, and neatly japanned on the outside, provided the hoop to which it is fixed below be made of copper; but this hoop must never be japanned nor painted, and it must always be made of sheet copper or silver, and the boiler must always be heated over a small portable fire-place or lamp, somewhat less in diameter above than the hoop on which the boiler is placed.
[Excursus on chafing-dish for heating.]
In order to convey distinct ideas of the different parts of the apparatus necessary in making coffee in the manner I have recommended, I have added the Fig. I, Plate IX., which represents a vertical section (drawn to half the full size) of a coffee-pot constructed on what I conceive to be the very best principles. Its size is such as is most proper for making four cups of coffee at once.
[Additional Rumford designs based on the same principles:]
a is the cylindrical strainer, into which the ground coffee is put, in order that boiling-hot water may be poured on it: when this strainer is filled with boiling water (after an ounce of ground coffee has been properly pressed down on its bottom), the quantity of the liquid is just sufficient for making four coups of coffee.
b is the ground coffee in its place.
c is the handle of the rammer which is represented in its place.
d is the reservoir for receiving the coffee which descends into it from the strainer; and
e is the spout through which the coffee is poured out.
f is the boiler, into which a small quantity of water is put, for the sole purpose of generating steam for keeping the reservoir hot.
g is the opening by which the water is poured into the boiler or out of it: this opening has a flat cover, which moves on a hinge that is represented in the figure. . . .
h is the hoop, made of sheet copper, and perforated with a row of holes, on which the boiler reposes: a part of the bottom of the boiler is seen through these holes.
The reservoir is represented by dotted lines, in order better to distinguish it.
The opening in the side of the boiler, by which the water enters it, is represented in the figure. This opening is covered by a part of the handle of the coffee-pot.
The diameter of the hoop h, on which the coffee-pot stands, should always be at least six inches in diameter, whatever may be the contents of the coffee-pot; and the spirit lamps or portable furnaces used with these coffee-pots should always be rather less than six inches in diameter above, or at their openings, in order that the bottom of the coffee-pot may, in all cases, be set down properly on the six knobs belonging to the lamp or the furnace, which are destined to support it. [1]
Notes
[*] Count Rumford (Benjamin Thompson), “Of the Excellent Qualities of Coffee and the Art of Making it in the Highest Perfection,” originally published in London in 1812, reprinted in The Complete Works of Count Rumford, vol. 4 (Boston 1875), 617–60.
Initial illustration from Der Freund des schönen Geschlechts: ein angenehm und nützlicher Taschenkalender für das Jahr 1808).
The keyed illustration is plate ix, figure 1, following 642. The non-keyed illustrations follow pp. 644, 656, 658.
These excerpts elucidate Rumford’s understanding of the science underlying the making of coffee and thus of using the coffee pots designed on his model, and his general philosophy of coffee drinking. Back.
[1] The Rumford coffee machine also plays a role in Hegel’s letters. Hegel writes to Friedrich Immanuel Niethammer from Bamberg on 13 October 1807 (Georg Wilhelm Friedrich Hegel’s Werke, ed. Marheineke et al., vol. 19, part 1: Briefe von und an Hegel, ed. Karl Hegel [Leipzig 1887], 1:134–36, here 135):
As far as my work is concerned, should you be tempted to ask, I can really only figuratively call it work. Although my journalistic duties [Hegel had begun editing the Bamberger Zeitung through Niethammer’s contacts] are indeed continuing in an uninterrupted, albeit joyless but also annoyance-free fashion, I find I need to introduce a bit more spirit into my activities, and in this connection I would like to request your help.
To wit, it seems to me that a Rumford coffee machine might be quite serviceable to that end, and since they are manufactured best or even exclusively in Munich, might I ask a favor of you or your most kind wife, namely, that you order one and have it sent to me and then forward the invoice to me as well. I will feel my existence has been significantly enhanced by such a meuble [Fr., here: “item furniture” in the sense of “household goods”] and will be greatly obliged to you for helping me secure one.
Hegel writes again to Niethammer from Bamberg on 22 January 1808 (Briefe von und an Hegel, 1:149–54, here 149):
My dear friend, I owe you not only a word of thanks, but also an apology for the delay in delivering that word of thanks, and, moreover, in sending you any answer at all; but I wanted to be in a position to relate to you how wonderful the coffee tasted from this machine, whose existence we owe to science — and how much my own scientific and scholarly activities already owe to this very coffee.
Unfortunately, in Bamberg science has, it seems, not yet exerted any influence on industry, hence neither can one really speak about the reflected influence of the latter on the former; perhaps a good question for a scholarly competition would be to determine just where one might get at this circle. In a word, neither my domestics nor the tin guild have been able to secure me a tin water kettle. The exact nature the thing that was delivered merits no further mention. Back.
Translation © 2017 Doug Stott