Louis Pasteur - The Man and the Legend of Spontaneous Formation Part III

And this time we will tell you how Pasteur saved the French wine industry

In 1854, at the age of 31, Pasteur moved to the University of Lille, where he served as professor of chemistry and dean of sciences. During his years at the University of Lille, Pasteur made his first discoveries related to single-celled organisms, and at the same time taught French winemakers how to make high quality wine in an efficient and safe manner.

Two years after Pasteur's arrival in Lille, he was called to help by Bigot, who was the father of one of Pasteur's chemistry students. Bigot the elder had a difficult problem: he tried to ferment beet juice to create alcohol, as was customary at the time. But instead of the beet juice being fortified with alcohol, Bigot received lactic acid in his fermentation tanks. Lactic acid is not at all like alcohol, especially in the opinion of the well-dwellers in France, and Mr. Bigot found himself on the verge of bankruptcy. Pasteur was his last hope. Bigot hoped that Pasteur could solve the mystery and make alcohol form in the beet juice fermentation tanks, instead of lactic acid.

In order to better understand the situation in those years, it is important to explain that chemistry then became an established and important science, in contrast to the alchemy that preceded it. Various chemists have succeeded in producing substances in a test tube that were previously thought only living creatures could produce. A chemist named Lavoisier showed that sugar can be turned into alcohol, water and carbon dioxide, simply by dripping a sugar solution onto a heated platinum plate. It is easy to understand, therefore, why most of the scientists of the time believed that the process of turning sugar into alcohol that occurs in beet juice or grape juice, occurs as a result of simple chemical reactions, and has no connection to living beings. The expert chemists of those days decided that sugar breaks down into alcohol during the fermentation process due to the presence of vibrations that destabilize the sugar molecule. They added and determined that these vibrations could be transferred from old fermentation tanks, thus restarting the fermentation process.

Today, of course, we know better. The fermentation process occurs due to the presence of yeast - tiny single-celled creatures - in the grape juice, or the beet juice. The yeast devours the large amount of sugar in the juice, breaks it down in order to produce energy, and as a byproduct they produce alcohol and secrete it into the solution. But in those days yeast was not considered to be of real importance in the fermentation process. The yeast in the wine was indeed visible under the microscope, but most scientists claimed that they were created in the fermentation process, or that they are nothing more than the catalysts that lead to the beginning of fermentation.

These opinions were based on previous experiments, and until Pasteur there were no scientists who were able to contradict them with successful experiments. But as Mr. Bigot's appeal to Pasteur demonstrates, those scientific opinions did not help the producers of wine, beer and vinegar. For them there was no way to know what the coming year had in store. In one year, there would be many fermentation barrels producing fine wine, and the rest would turn into vinegar. The next year, all the barrels would produce a weak solution of lactic acid, or vinegar. The wine could unexpectedly turn sour, or turn bitter, or go bad. There was, in fact, no way to control the creation of the wine, its taste or its quality. All the producers could do was cross their fingers and hope for good luck at the start of each fermentation year.

Pasteur went deep into the mystery of wine fermentation. Every day he would come to Bigot's factory, microscope in hand, to examine barrels and fermentation samples. Madame Pasteur noted dryly that he would return, "soaked up to his neck in beetroot juice" [D]. The experience that Pasteur acquired in using the microscope served him well in the study of fermentation as well. Already on the first day, when he examined the beet juice samples under the microscope lens, he noticed globules that grew and more globules appeared in the liquid. These pellets were found in the beetroot juice that fermented well and turned into alcohol. It was yeast, which turned the sugar into alcohol. In contrast, in the beet juice that turned into lactic acid, Pasteur discovered another type of tiny creatures, which were smaller and longer than the yeast. These bacteria would take over the fermentation barrels and would turn the sugar into lactic acid, instead of letting the yeast turn it into alcohol.

Pasteur showed Bigot how to use a microscope to examine the different fermentation tanks. He explained to him that if bacteria appear in the solution, then no alcohol came out of this keg. But if instead of the bacteria, there is yeast in the juice, then the alcohol is the one that is produced inside the barrel.

We know today that yeast and bacteria are living things. But how did Pasteur prove it?

Pasteur suspected from the beginning that these were living creatures, due to the theory he was trying to promote, according to which asymmetry is associated with living creatures. He believed that just as chiral tartaric acid is produced by living things, so also alcohol, lactic acid and a variety of chiral substances are produced by living things, which are the same balls and sticks. In order to prove the claim, Pasteur did a simple and elegant experiment, as usual. The basis of the experiment was Pasteur's hypothesis that the 'balloons' use sugar as food, and turn it into alcohol. Pasteur showed that the less sugar there is in the solution, the higher the mass of the yeast in that solution. He also measured the solutes and the carbon dioxide in the solution, and showed that it is not possible that all that sugar that 'disappeared' turned into carbon dioxide and other solutes. It is clear that the yeasts are the ones that used the sugar to produce energy, to increase the cell volume and to constantly divide.

Pasteur showed beyond any doubt that, "Alcoholic fermentation never occurs without being accompanied by the organization, development and division of cells, or the continuation of the life of cells that already exist." He confessed that he was unable to understand the complex processes by which the yeast turns sugar into alcohol, but rightly claimed that, "the facts show me simply that all true fermentations are connected with physiological processes." [E]

In the first article that Pasteur published about fermentation, he described to the captivated audience at the university how he studied the fermentation process in depth, and how he was able to isolate and grow the fermenter that creates lactic acid and the fermenter that creates alcohol. He demonstrated how he was able to create two pure solutions - one in which only lactic acid fermentations grow, and a second solution in which only alcohol fermentations grow. In the solution with the lactic acid fermenters, only lactic acid was formed. In the solution with the alcohol fermenters, only alcohol is formed. He also showed that the fermenters must be alive in order to work, thus demonstrating for the first time the pasteurization process, during which wine or milk is heated to a temperature high enough to kill most of the organisms in the solution, but not high enough to destroy the taste and texture of the drink. The pasteurization process still exists today, mainly in pasteurized milk, and it kills most of the bacteria, fungi and other single-celled organisms that could harm our stomachs.

By exposing Pasteur's experiments to the general public, we also discover for the first time his ability to captivate the audience with his words and experiments. Pasteur was a master of public performance and scientific communication. He made every person in the audience understand the scientific research process and feel as if he himself was conducting the experiments on stage. He would bring the simplest experiments and conduct them, if possible, before the astonished eyes of people from all walks of life. Throughout his life, Pasteur used his ability to simplify science for the public and used it to gain public acceptance of the results of his research. Much of the criticism leveled at him today stemmed from Pasteur's ability to manipulate the politics surrounding his research and pull strings to gain support for his research and opposition to the research of his opponents. He was a brave man, yes. Ambitious, certainly, and merciless in his mockery and anger towards anyone who did not agree to accept his experiments as pure truth. Pasteur's luck - and ours - is that he worked hard enough and conducted enough experiments to substantiate in his eyes the conclusions he presented to the public. Indeed, the same conclusions are still valid today, after thousands of scientists have proven them in thousands of different experiments.

Before we finish reviewing this period in Pasteur's life, we will look at another important discovery he made at the end of his research on fermentation. Between 1857 and 1863, Pasteur published article after article in which he identified the fermenters that cause various fermentations, and described their living conditions and of course - how they can be killed. In 1861, Pasteur was able to show that the microorganisms that lead to the formation of butyric acid are unable to live in an environment with free oxygen. He noticed the phenomenon in a routine experiment during which he dripped a drop of lactic acid fermenter on glass, and examined it under a microscope. He noticed that these fermenters try to move to the edge of the droplet, where they are exposed to more oxygen than the air. On the other hand, when he dripped a drop with butyric acid fermenters on the glass, he noticed that the same fermenters tried to move away from the edge of the drop and stay in the center. The obvious conclusion was that they avoided the oxygen in the air. To verify the diagnosis, Pasteur conducted additional experiments in which he proved that the butyric acid ferments can live without oxygen - and in fact, that exposure to oxygen can kill them.

Pasteur called the microbes that could live in the presence of oxygen 'aerobes', and the microbes that could live without oxygen 'anaerobes'. These definitions have since become the basis of the science of microbiology, and today we make sure to specify for each single-celled organism whether it is aerobic or anaerobic. Many dangerous bacteria are anaerobic, including the bacterium that causes tetanus.

When Pasteur used his new insights and tested the yeasts that lead to alcoholic fermentation, he discovered that they were able to live both in the presence of oxygen and without it. At the same time, he revealed the fact that when the yeast is not exposed to oxygen, it is able to turn sugar into alcohol with a very high efficiency. When the yeast is exposed to oxygen, the process is not as efficient and most of the sugar turns into water and carbon dioxide. This effect is still called the 'Pester effect'. The practical application of the Pasteur effect resulted in the improvement of the wine and beer production process. The manufacturers received explicit instructions from Pasteur that they must make sure their fermentation tanks are well sealed, in order not to allow the yeast to breathe oxygen from the air and spoil the alcohol production.

When Pasteur decided to turn his attention to the issue of spontaneous formation in 1859, he left behind six years of research that made France a wine powerhouse in Europe. After France lost the Franco-Prussian War in 1870, the huge profits made from the great trade in fine wines enabled France to pay Germany the 5 billion francs it demanded as reparations. And of course, the excellent wines delighted the heart of the French nation and left a sweet taste even after the great defeat.

Tomorrow we will conclude the chapter discussing Louis Pasteur with Part D, in which we will see how everything we learned in this chapter amounts to the refutation of spontaneous formation and Pasteur's fight against that myth.

Part I of the article
Part B of the article
Part D of the article