The early years 1847-1862

In 1847 Louis Pasteur, a young chemist freshly graduated from the prestigious Ecole normale supérieure, set to work on the problem posed by German physicist Eilhard Mitscherlich, namely, why do sodium ammonium paratartrate and tartrate - two seemingly identical chemical substances - affect polarized light differently ?


Crystallography and molecular asymmetry

1847: research on molecular asymmetry

After several years of research involving crystallography, chemistry and optics, Louis Pasteur drew a parallel between the external form of crystal, its molecular make-up and its effect on polarized light. He discovered that asymmetric crystals deflect polarized light whereas this is not possible for crystals with a plane of symmetry.

He established a law of primary importance. " Only products originating under the influence of life are asymmetrical because they developed under the influence of cosmic forces which were themselves asymmetrical. " Asymmetry is the major dividing line between the organic and mineral worlds.

Louis Pasteur’s work led to a new science: stereochemistry or spatial chemistry. It was also behind the emergence of synthetic chemistry.

Fermentation, a life’s work from 1857 to 1862

1857: beginning of research on fermentation

It was while observing paratartrate crystals that Louis Pasteur discovered molecular asymmetry. When examining a paratartaric acid solution, he also noticed that the acid had fermented and been dissociated under the effect of mold. The fermented liquid now only contained left tartaric acid. The right tartaric acid had been decomposed or " disassembled ". Thus a substance inactive on polarized light (paratartaric acid) had become active (left tartaric acid) under the effect of fermentation.

Before these findings it was universally acknowledged that fermentation was a death process according to the belief of the famous German chemist, Justus von Liebig. On completion of these experiments Louis Pasteur established a theory that ran counter to this dogma. Since all active substances come from the living environment, fermentation is a life process. Only life generates substances that are active on polarized light.

Through a logical sequence of studies, it was this initial observation that led from molecular asymmetry to fermentation and then on to contagious diseases.


1857-1862: beginning of research on fermentation


In 1854, at the age of 32 years Louis Pasteur was appointed Dean of the Science Faculty in Lille.

He was soon contacted by several of the region’s many distilleries. The distillers were concerned about variations in their beetroot alcohol production. They therefore requested Louis Pasteur to focus research on lactic acid and alcohol fermentation.

He noted that :

  • alcohol fermentation is due to a living organism - ferment
  • to study fermentation you need to:
  • prepare a sterile fermentable culture medium, obtained through boiling
  • inoculate the medium with a trace of pure ferment.

This was the basis of all microbiological techniques.

In studying the fermentation mechanism that confirmed the role and specificity of microorganism action, Louis Pasteur began to turn to biology. From this moment on he was no longer a mere chemist but also a biologist.

This marked a new period in his work.



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