Wrote Letter 54 of 1687-05-09 (AB 99) to Members of the Royal Society

May 9, 1687
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Leeuwenhoek's summary

From all editions of Vervolg der Brieven and translated into Latin for all of the editions of Continuatio Epistolarum.


In wat ordre de Meelachtig stoffe in de Zaaden werd ingestort. Van de Coffee-boonen: in wat deel van de Coffee-boon de jonge plant leyd. De jonge plant uyt de Coffee-boon genomen. Bloemkens die op de jonge plant van de Coffee-boon zyn uytgewassen. Zout ende veel oly in de Coffee-boonen; Geen meelachtige stoffe in de Coffee-boonen; ende daarom moeten de selve geroostert zyn, eer die tot een poeyer konnen gebracht werden. Dat men de Coffee-boonen weynig behoort te branden, en syn te stooten. Het maaksel van de Coffee-boonen. De Coffee-boonen in een weynig water geleyt, krijgen een gras-groene couleur.


In what order the flour-like substance is poured into the seeds. Of the coffee bean, in what part of the coffee bean the young plant lies. The young plant taken from the coffee bean. Little flowers that are growing out of the coffee bean. Salt and a lot of oil in the coffee beans; no flour-like substance in the coffee beans; and thus the same must be roasted, before it can be made a powder. That one properly roasts the coffee beans, and pounds them. The structure of the coffee bean. The coffee beans lying in a little water get a grass-green color.

Text of the letter in the original Dutch and in English translation from Alle de Brieven / The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren.

The original manuscript, written and signed by Leeuwenhoek, is preserved at the Royal Society (MS. 1917. L 2. 8).

Reception in London

Five days after it was written, this first part of this letter was read at the meeting of the Royal Society on May 4/14, 1687 (O.S./N.S. Birch's History, vol. IV p. 534, 540):

Part of a letter of Mr. Leeuwenhoeck of May 9, 1687. N. S. was read, containing some microscopical observations on the structure or constituent parts of the mealy pabulum of plants, included together with the embryo plants in the hulk of the seed. This he had found in the kernel of a medlar-stone to consist of nothing else but conglomerated globules. The rest of this letter was ordered to be translated.

Three weeks later, they got to the rest of the letter.

A letter of Mr. Leeuwenhoeck's was read concerning coffee, first as to the growth and texture ofthe coffee-berry, wherein he found very much oil to be contained; in which oil he conceived the principal virtue of the coffee to lie; and prosecuting that notion he gave direction for roasting the berry, and making coffee drink after the best manner. In the conclusion he said, that the coffee-berries grow on a tree as big as our lime trees, as he had been credibly informed.

How Leeuwenhoek made his morning coffee

In the text, Leeuwenhoek shared one of his personal preferences.

But as far as I am concerned, I have the coffee, which I have been drinking now and then for about a year, only slightly roasted, and this coffee is then ground so fine, and sifted through a silken sieve, that one cannot with the finger feel the slightest hardness in it, exactly as if one had flour between the fingers.

Of this coffee a certain quantity is put into a coffee pot, and then water is poured on it that has boiled for some time and is still boiling, after which this coffee is again put over the fire, but not so long that it boils; and then, after it has stood away from the fire for a little, I drink that coffee beverage.

Specimens and methods: sectioning coffee beans

Plate from
Continuatio Epistolarum

Figures 1 - 7

The problem with examining a dense specimen like a coffee bean was lighting it. Leeuwenhoek made sections thin enough that light could pass through them.

I have cut off a tiny flake from a coffee bean (after first cutting a piece off), and held it before a microscope, only to indicate to Your Honours the open or spongy Parts of which a Coffee bean consists.


The original drawings are lost. The Dutch and Latin editions that Leeuwenhoek published used the same plate with all seven figures. The one on the left (click to enlarge) came from the 1730 fourth edition of Continuatio Epistolarum, as did the images on the sidebar. In the text, Leeuwenhoek noted that someone else drew the figures.

Now in order to visualize this and get a better understanding of it, I have thought fit to have some of this flour-like substance (which would have constituted the kernel) to be drawn, as it appears before a microscope.

Other publications

While the Royal Society did not publish this letter in Philosophical Transactions, it was extracted twice in foreign journals, as were all the letters in Vervolg der Brieven, Letters 53 through 60. In the year after it was written, Jean Le Clerk published an excerpt, without any figures, in Bibliothèque universelle et historique, vol. 9, pp. 294-297.

In 1689, Otto Mencke pubished a very short extract, again without figures, in Acta eruditorum, vol. 8, p. 172.