Museum
Studies on wine: the 160th anniversary of a scientific revolution in viticulture
To mark the 160th anniversary of the publication Études sur le vin (Studies on wine), as we find ourselves in this year's grape harvest season, the Pasteur Museum takes a look back at Louis Pasteur's research among wine producers in the Jura region, which laid the foundations for modern winemaking.
An imperial commission prompted by an economic crisis
The free trade agreement between Emperor Napoleon III and Queen Victoria, signed in January 1860, opened the British market up to French wine. But hopes of a boon in exports were soon dashed when many of the wines were spoiled during transportation, becoming bitter or cloudy. The French wine industry, the jewel in the crown of the country's economy, was at risk.
In July 1863, the Emperor turned to Louis Pasteur, who was already known for his work on the fermentation of alcohol and lactic acid, and officially commissioned him to study the causes of wine spoilage and what could be done about it.
A return to the Arbois wine region
To carry out his research, Louis Pasteur decided to go back to his childhood region of Jura and the town of Arbois. He set up a field laboratory, first in a former canteen and then in the Maison Gerbet, and began to study the daily practices of winemakers. Armed with his microscope and accompanied by fellow scientists and local winemaker friends, he visited wine cellars, listened to those working in the sector and analyzed dozens of samples.
His first conclusion took many by surprise: the spoilage was not the result of a spontaneous process within the wine. It was caused by living microorganisms transported by dust in the air.
Every disease caused by a different type of bacteria
As he continued his observations, Pasteur produced a detailed clinical picture of the various diseases affecting wine, identifying the microorganism responsible for each:
- Acetification, or acetic souring, is a process in which wine is turned to vinegar by Mycoderma aceti, known today as Acetobacter aceti, bacteria that proliferate on the wine's surface when it comes into contact with air.
- Amertume (bitterness) particularly affects old wines, when the color pigments and glycerol are attacked by lactic acid bacteria mainly belonging to the genera Lactobacillus and Pediococcus.
- Tourne makes the wine cloudy as a result of filamentous lactic acid bacteria that break down tartaric acid, the main acid in wine, and increase the pH level.
- Maladie de la graisse, also caused by lactic acid bacteria, gives wine an oily, ropey consistency and affects the taste.
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The solution: heat wine in an airtight environment
On April 11, 1865, Louis Pasteur filed a patent for a "process for the preservation of wine through mild heating away from air." The principle is simple: heating the wine for a few minutes at a temperature between 50°C and 65°C destroys the parasitic germs without negatively affecting its sensory qualities (taste, smell, appearance). But Pasteur insisted that the process had to be performed without contact with air, to avoid oxidation.
The procedure could be applied to bottles, using a bain-marie, or to wine in barrels using a copper coil inserted through the bung hole. Industrial devices were soon developed, such as the appropriately named Œnotherme and Thermæphylactique, and renowned wineries adopted the method.
The method, initially applied to wine, was extended to beer (1871) and then milk (adapted by Franz von Soxhlet in 1886). The "pasteurization" process was born.
September 22, 1866: publication of Études sur le vin
On September 22, 1866, Louis Pasteur published a summary of his research: Études sur le vin, ses maladies, causes qui les provoquent, procédés nouveaux pour le conserver et pour le vieillir.(Studies on wine, its diseases, what causes them, new processes to preserve and age it). The book combines existing knowledge, from Van Helmont (1579-1644) to Chaptal (1756-1832) and Gay-Lussac (1778-1850), with microbiological rigor, chemistry and sensory tasting. It is illustrated with engraved plates representing the "organized ferments" observed under the microscope, produced by Pierre Lackerbauer (1823-1872).
Louis Pasteur's work and findings on the heating process earned him immediate recognition – he was awarded the Grand Prix and a prize for "Agricultural Merit" at the 1867 Paris Exposition.
The term "pasteurization" entered the vernacular and is used the world over to refer to the process of preserving food through moderate heating (it is known as Pasteurisierung in German and pasteurzacion in Spanish, to name just two examples).
Further information
Études sur le vin, ses maladies, causes qui les provoquent, procédés nouveaux pour le conserver et pour le vieillir (Studies on wine, its diseases, what causes them, new processes to preserve and age it), Louis Pasteur, 1866: available at Gallica, BnF
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