What is an alcoholic fermentation?

 

We have come a long way to understand alcoholic fermentation.

As early as the second millennium BC, the Paleo-Babylonians and perhaps others people (Egyptians, Indians) before them had identified and named a beige and greasy material collected in two ways. Either by recovering the beer dregs from the bottom of the jars, or by collecting the beige supernatant from the scum at the time of the tumultuous fermentation of beer. Once dried in the sun on a porous surface (wall, pottery shard, plant fibres, skins, etc.), the precious substance was used to revive the next brew or to make the bread leavening.

For thousands of years, man has been observing fermentation and making leaven. But before the year 1680, nobody had ever seen a yeast!

 

 

1st act

The first act of this adventure is the observation of living beings. In 1680, a Dutchman saw animalcules in beer with his own eyes and drew them. Antoni van Leeuwenhoek (1632-1723) lives in Delft, Holland. He writes: "Droplets floating in a clear substance; each was made up of six separate 'globules', which are the same size and shape as the globules of our blood" (letter to Thomas Gale, 14 June 1680).

Deux modèles de globules de levures de bière.Two "globules" of brewer's yeast observed by Van Leeuwenhoek. Drawing in sanguine pencil. Letter of 14 June 1680. After Ph. Boutibonnes, Antoni Van Leeuwenhoek 1632-1723. L'exercice du regard. Belin 1994.

 

Van Leeuwenhoek has just observed the multiplication of Saccharomyces by budding. He also notes the presence of bubbles which " come up in abundance from the lower part of the beer and settle on the surface "[1]. His mother Grietge Jacobstr van den Berch came from a family of brewers, as did his first wife Barbara de Mey. He was able to obtain samples of beer in the middle of fermentation, observed with one of his monocular microscopes he had built. With 2 or 3 lenses, it could magnify up to 300 times. A resolution of about 1.4 µm enabled him to draw precisely a few yeasts of 10 to 50 microns.

For more than 30 years, Leeuwenhoek's microscopy has been observing all this tiny world swarming around him. As a remarkable optician, preparer, observer and designer, he describes cross sections of seeds, certainly barley or malt with their germs :

« But the most remarkable point is this: just as the animal, in the womb, is fed by a cord which consists of many vessels, and allows it to grow, I believe that the grains that I have examined also possesses an identical cord; the cord is, in one case or another, either very short or very long - it exceeds then the size of the whole seed » (letter of 13th July 1685). This 'cord' is the plumule of malted grain (among other examples of germinating seeds described by Leeuvenhoek).

Jan Verkolje - Antonie van Leeuwenhoek

 

« We will see Him (the Creator) has not only placed in all grains a young plant in reduction, but also a material close to the flour, in which the plant is housed and which serves as a primary food; but that it is also various seeds in which there is no such nutrients and which are filled with the various parts of the plant itself » (letter of 13th june 1687. Boutibonnes 1994,134). Leeuwenhoek fuels a debate that will span the 18th-19th centuries between the defenders of "spontaneous generation" - the living is born only from the living -, and the partisans of animate or inanimate mechanics - matter follows only the laws of physics and chemistry [2].

In 1697, Georg Ernst Stahl, chemist and physicist at the Prussian court published his Zymotechnica Fundamentalis (Foundations of Fermentation Techniques). He advocates a study of fermentation by means of chemistry, an approach free of the alchemical conceptions of the time. Fermentation is a recombination of inanimate material elements that chemistry can analyse. However, Stahl only discusses the principles, without providing any quantitative analysis. The scientific approach to fermentation, made up of described and controlled experiments, with verifiable measurements, came into being a century later with the rationalists of the 18th century and the bi