Fermentation is a technique that has been mastered by the human for a long time. It is a process where microbes produce enzymes that can change the chemical composition of organic substances to make products at our sweet will. We can find fermentation in every culture, every legend. People have been using this process or we can say using microbes for much longer than we know. The evidence says that Babylonians learned to make beer around 6000 B.C. and Chinese and Egyptians used microbes to brew grain-based beverage and bread respectively as long as 4000 B.C. But how did it start? Maybe it started unwillingly when a wild yeast or other microbes took place in a bowl of food or jug of juice and found suitable conditions for fermentation!! Then maybe humans noticed the incident several times and started to embrace this technique for their benefit.
However, the true mechanism of fermentation remained a mystery until the late-ninetieth or twentieth century. In fact, this is one of the most favorite problems among many scientists. The researchers believed three different theories at that time. As a result, the controversy was started!! The main theories were: chemical, vitalist and modified chemical.
The chemical theory was built by many scientists, specially German chemist Justus von Liebig. Earlier this, French chemist Lavoisier, Gay-Lussac, Thenard and Dumas researched the transformation of carbohydrates into alcohol by quantitative methods. Among them, Lavoisier developed a simple formulation of the natural breakdown of organic substances where there was no place for any microbes or yeast. Most of the chemists of that time accepted that yeast only began the process but did not take any part in this. Berzelius defined this incident as catalysis. Following Lavoisier, Liebig considered fermentation as a chemical decomposition which is occurred by the putrefaction of organic materials. He also rejected the term catalysis and the theory accepted by others about the fermentation’s initiation by yeast. Instead, Liebig said vibrations from the putrefaction could be the reason for the beginning of the process. But in alcoholic fermentation, he took for granted that yeast was used in the process only for triggering the fermentation like a putrefied vegetable matter! And nitrogen-rich ferment could cause fermentation in other carbohydrate solution. He believed the ferment needs oxygen, water and appropriate temperature. He also added that the elements of the ferment could get disturbed before the reaction and separated or could make new arrangements. As a result, fermentation could be started because of the instability of ferment. Liebig’s views on fermentation were entirely based on Physico-chemical laws where yeast or other microbes failed to occur.
On the other hand, some scientists have completely different ideas. French chemist Louis Pasteur known as the father of fermentation in the modern world developed several theories about fermentation from 1857 to 1860. He believed in Cagniard de La Tour and Schwann’s findings, where they identified growing live yeast in the sugar ferment. The father of fermentation believed in vitalism and said that fermentation was occurring by the living microorganism’s biological activity. He also added those specific organic substances in fermenting medium worked as food for the particular microorganisms and they change the composition of these substances for their growth. Pasteur strongly rejected Liebig and other scientists’ theory and interpreted that fermentation is related to the living and their organization, not accomplished by decomposition or putrefaction.
But as we know the science behind fermentation today, can we say that Pasteur was right? Before answering this question, we should know the third theory about fermentation given by another French chemist Marcellin Berthelot.
Marcellin Berthelot was a contemporary scientist with Liebig and Pasteur who also worked on fermentation. He acknowledged the connection between microbes and fermentation but didn’t believe in the vitalist theory completely. He hypothesized that microorganisms didn’t change the composition of the organic substances directly. Instead, it produced an organic compound that can work without the presence of the microbes and can change the organic material of the fermenting medium. In his work Organic Chemistry Founded on Synthesis (1860) he wrote that “ferment is not the living organism, but the substances produced by one.” In the present time, we are calling this ferment as the enzyme.
Among these theories, Liebig’s ideas are wrong. His chemical approaches didn’t show any future scopes to study on fermentation. On the opposite, Pasteur works aren’t convincing according to today’s knowledge but he provides immense opportunities to research further and find the real causes of fermentation. But strictly say he failed to define the fermentation as accurately as Berthelot did.
In conclusion, we can say these hypotheses correct or incorrect only compare to today’s knowledge. Still, we all have to agree that this is how science has been progressing since the beginning.
Department of Biochemistry and Molecular Biology,
University of Chittagong.
A story taken from Acevedo and Garcia-Carmona, 2016