In 1855, then dean of the Faculty of Sciences of Lille, Louis Pasteur was seized by the father of a student, a sugar industrialist, of the problems of several manufacturers: their beet alcohol sometimes took on an acid taste and nauseating vapors came out tanks.

The chemist notes that the alcoholic fermentation is due to living organisms, the ferments, and that, in the defective fermentations, appear small rods producing lactic acid.

He then highlights, in his Parisian laboratory at the Ecole Normale Supérieure, that each fermentation results from a specific micro-organism.

The chemist also discovers a new class of living beings, capable of living in the absence of air.

He proposes the terms "anaerobic" for ferments capable of living without air and "aerobic" for micro-organisms that need free oxygen.

Microscopes or gooseneck flasks, the researcher explores fermentations with laboratory instruments.

He also investigates in the field, buying a small vineyard (Clos des Rosières) in Arbois, the Jura town of his childhood, and studying the practices of various wine-growing localities and sick wines.

Microscopes in "La salle des Actes" at the Institut Pasteur, in Paris STEPHANE DE SAKUTIN AFP/Archives

The wine and its vagaries are then a concern to the top of the State.

Napoleon III is interested in a problem that had already preoccupied his uncle, Napoleon I.

Louis Pasteur shows in particular that heating the wine denatures the problematic ferments and allows it to be kept intact in the bottle.

The wine is heated between 55°C and 60°C, a temperature at which it does not deteriorate and keeps its bouquet.

A method to which he gave his name, pasteurization.

"His work on wine is pioneering, it opens our eyes to the diversity of microbes, the processes that initiate them, the importance of oxygen...", notes Gabriel Lepousez, neurobiologist at the Perception and Memory research laboratory. at the Institut Pasteur, which likes to use gastronomy and wine to popularize science.

On the strength of these discoveries, Louis Pasteur also immersed himself, in particular at the request of a brewer from Chamalières, in the problems of beers, sometimes altered by micro-organisms from dust in the air.

He teaches brewers to preserve musts from contamination and to heat beer to 55°C to prevent disease.

Louis Pasteur taught brewers to preserve musts from contamination and to heat beer to 55°C to prevent diseases Kenzo TRIBOUILLARD AFP/Archives

This work on fermentations and micro-organisms will then open up a path for Louis Pasteur to understand infectious diseases.

If the pasteurization of wine will end up being cut short, "Pasteur will be a school" by his work on wine, underlines Gabriel Lepousez.

The neurobiologist evokes one of the researcher's disciples, the chemist Ulysse Gayon, founder of the oenological institute of Bordeaux, inventor of "Bordeaux mixture" - the copper sulphate used to fight mildew -, and ancestor of the creator of the famous oenological school of Bordeaux.

Another filiation: "In the 1950s, we discovered that after alcoholic fermentation another fermentation takes place, by bacteria, which, well controlled, will allow a lactic acid bacterium to bring out other aromas", says Gabriel Marry him.

"All the work of modern oenology has been Pasteur work, understanding this phenomenon and controlling these fermentations".

© 2022 AFP