Fermentation theory
Notable contributors to the theory include Justus Von Liebig and Louis Pasteur, the latter of whom developed a purely microbial basis for the fermentation process based on his experiments.
Pasteur's work on fermentation later led to his development of the germ theory of disease, which put the concept of spontaneous generation to rest.
Fermentation has been used by humans consciously since around 5000 BCE, evidenced by jars recovered in the Iran Zagros Mountains area containing remnants of microbes similar those present in the wine-making process.
[4] This theory was corroborated by Liebig's observation that other decomposing matter, such as rotten plant and animal parts, interacted with sugar in a similar manner as yeast.
[4] A different theory was supported by Charles Cagniard de la Tour and cell theorist Theodor Schwann, who claimed that alcoholic fermentation depended on the biological processes carried out by brewer's yeast.
[6][5] Louis Pasteur's interest in fermentation began when he noticed some remarkable properties of amyl alcohol—a by-product of lactic acid and alcohol fermentation—during his biochemical studies.
[6][7] Pasteur had previously been attempting to derive connections between substances' chemical structures and external shape, and the optically active amyl alcohol did not follow his expectations according to the proposed 'law'.
[4][6] According to a legend originating in the 1900 biography of Pasteur, one of his chemistry students—an owner of a beetroot alcohol factory in Lille—sought aid from him after an unsuccessful year of brewing.
[5][6] This also disproved Liebig's theory, since there was no albuminous matter present in the medium; the decomposition of the yeast was not the driving force for the observed fermentation.
Aristotle, an ancient Greek philosopher, theorized that creatures appeared out of certain concoctions of earthly elements, such as clay or mud mixing with water and sunlight.
[5][6] On top of this, a common piece of evidence that seemed to corroborate the theory was the appearance of maggots on raw meat after it was left exposed to open air.
When the swan-neck flasks failed to show these same microbial growths, Pasteur concluded that the structure of the necks blocked the passage of atmospheric dust into the solution.
[6] Thus, Pasteur's work provided proof that the emergent growth of bacteria in nutrient broths is caused by biogenesis rather than some form of spontaneous generation.
