… the man who turned vinegar in to wine: Louis Pasteur

[The Leaven – exploring the relationship between science and religion (cont)]

Mendel and Darwin worked in a parallel universe. They were both theologians whose discoveries emerged at the same time and resulted from a similar method of meticulous observations. Mendel’s work did not cause an upheaval equivalent to that of Darwin’s, as it described the laws of nature and did not directly threaten orthodox beliefs. Attention was focused mainly on the findings of Darwin and Wallace and, as a consequence the significance of Mendel’s results remained unappreciated until the beginning of the 20th century. The integration of Mendel’s findings with those of Darwin’s led to a greater understanding of inheritance and evolution but digressed from the common belief that Earth evolved only a few thousand years ago and that each species was created within a similar time-scale. Simarly, Pasteur’s research  eradicated the idea that organisms could spontaneously generate. Using sophisticated apparatus, he prevented microbe-contaminated air from passing into a nutrient broth. This demonstrated that microbes could not be generated spontaneously under sterile conditions.

Louis Pasteur made great advances in microbial research especially when it had industrial connotations. His doctorate thesis was in researching the crystalline structure of two compounds found in fermenting wine, these were tartaric and paratartaric acids. The structures of these two compounds were identical but in solution they rotated polarised light in different ways. Pasteur established that this was due to chirality; he discovered that one structure was the exact mirror image of the other, rather like a left and right shoe. Science has now established that all living organisms only synthesise left-hand amino acids and can only utilise right-hand carbohydrates, left-hand carbohydrate compounds are synthesised artificially. Pasteur suspected that one of the molecules in wine was artificial while the other had been synthesised by a living organism; it was this organism that was responsible for wine fermentation.

During the time Pasteur was researching chirality, alcohol production was thought to be a chemical reaction. Lavoisier had demonstrated that if a sugar solution was dropped on to heated platinum it produced carbon dioxide, water and alcohol. It was therefore reasonably assumed that the production of wine, beer and vinegar was simply caused by a destabilising chemical chain reaction. By transferring some of this destabilised solution to a vat of sugar and grape juice the momentum of the chain reaction would continue. Yeast cells were known to exist in fermenting wine but were just thought to be an incidental byproduct. Around about this time, French wine production was inconsistent because spoilt wine contributed to great economic loss. Pasteur was asked to research a problem concerning lactic acid contamination in beetroot fermentation. Pasteur noticed that whenever fermentation took place yeast cells were present. He also noticed that when lactic acid was produced smaller rod shaped microbes appeared. In addition he observed that compounds other than those formed through the degradation of glucose were present and these tended to be asymmetric.

Louis Pasteur by Albert Edelfelt (1885)

Pasteur deduced that living cells were responsible for wine fermentation and contamination. He also established that if the wine was heated before fermentation commenced then the microbes were killed and the wine remained free from contamination. The procedure of heating to sterilise came to be known as pasteurisation and is today applied to many foodstuffs. One of its most notable applications, and perhaps most beneficial as far as health management is concerned, has been in sterilising milk. Milk as a rich source of protein, was at one time infected by many pathogenic bacteria, including those responsible for common diseases such as tuberculosis and brucellosis. It was through continual development of his knowledge in microbiology and sterilisation methods, that allowed Pasteur to disprove the spontaneous generation theory. Using sophisticated equipment he found that he could physically exclude air-borne microbes from a vessel containing boiled meat thereby preventing contamination His many contributions to science did not finish here he also went on to develop vaccinations against anthrax and rabies infections. The French government funded the Pasteur Institute to allow him to treat rabies victims. His fame transcended the Atlantic were another three Pasteur Institutes were set up.

In 1818 slightly prior to the spontaneous generation experiments conducted by Pasteur, Erxleben put forward a theory that a biological interaction was responsible for fermentation. Renewed interest in this theory led to a number of experiments, in the 1830’s, by Cagniard de la Tour, Schwann and Kützing. They proposed that fermentation was caused by a biological organism that used sugar as a food excreting waste substances in the form of alcohol and carbon dioxide. Many chemists of this period disagreed with this theory, they thought that the fermentation process was entirely physical and did not involve any biological activity. Von Liebig proposed that fermentation was completely mechanical involving a substance that continually processed a chemical transformation causing sugars to degrade into ethanol and carbon dioxide. This argument was resolved by the work of Louis Pasteur. In 1876 Pasteur published a book, Études sur la bière, in which he proposed that microorganisms obtained energy in anaerobic conditions by fermentation. His theories were supported by experimental evidence later supplemented by the work of Meyerhof. The fundamental metabolistic behaviour of yeast is now known as the Pasteur-Meyerhof reaction. There was a brief return to von Liebig’s chemical theories following the discovery that the cell-free juice of yeast extracted by a mechanical press could initiate fermentation. This cell-free juice was called zymase and is now known to consist of enzymes. In fact, the word enzyme, derived from the Greek term for yeast, originates from this discovery. This extract was unstable but still allowed the chemical and catalytic reaction that turn sugar into alcohol and carbon dioxide. It eventually, became generally accepted that this reaction was only sustainable in yeast cells. It was a chemical reaction that provided the yeast cell with the energy of life, life in one of its most simple forms but with a huge impact on the evolution and culture of mankind.


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