Fermentation theory

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Louis Pasteur, Archives Photographiques

The fermentation theory was studied in depth and brought to light first by Louis Pasteur. This theory states that it is the idea or concept of how fermentation is brought on by microbes and put to the concept of spontaneous generation to rest.[1] Even though this theory is now outdated and has been replaced by the germ theory of disease, for a long time it held true, and Louis was on the forefront of explaining why it seemed organisms appeared out of nothing instead of claiming it was just a spontaneous act of God. Fermentation was a process that has been used for thousands of years, but no one could explain exactly what was happening and why. From Pasteur's discovery of why and how fermentation occurs, the process has been studied intensely and is now a mastered art used in everyday life with processes of making things such as alcoholic beverages, some foods like yogurt or even manufacturing some medications.[2][3]


Process of Fermentation

Simply put, fermentation is the anaerobic metabolic process that converts sugar into acids, gases, or alcohols. This metabolic process is used in oxygen starved environments. Yeast and many other microbes commonly use this process in order to carry our their anaerobic respiration to survive. Even the human body carries out fermentation processes from time to time. When someone runs a long distance race, lactic acid will build up in their muscles over the course of the race. That lactic acid is the by-product of fermentation taking place in their body, which tries to produce ATP so the body can continue to run since they could not process the oxygen intake fast enough. Although fermentation will give a lower yield of ATP production than aerobic respiration does, it can occur at a much higher rate. Fermentation has been used by humans consciously since around 5000 BCE where there were jars recovered in the Iran Zagros Mountains area in which contained remnants of a microbes similar those present in the process of making grapes into wine.

Example of a typical curved neck used today

What the Theory is[edit]

Before the 1870s, when Pasteur published his work on this theory, it was believed that microorganisms and even some small animals such as frogs would spontaneously appear, which was coined as spontaneous generation. Spontaneous generation was the explained theory that when elements of the Earth such as clay or mud would mix with water and sunlight in certain amounts, creatures would just appear out of that concoction. A common way that this idea was "proven" over and over again was by taking a piece of raw meat and placing it in open air, which would almost always produce maggots. This idea was accepted and believe to be true before Louis Pasteur shook the Earth with his new ideas that organisms actually came from traceable beginnings.[3] Pasteur demonstrated that fermentation is caused by the growth of microorganisms, and the emergent growth of bacteria in nutrient broths is due to biogenesis rather than spontaneous generation. He exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium.[4] Yet, when the vessels were open to the air surrounding it, the organisms appeared. It could be concluded that spontaneous generation could be disproven. The organisms did not just appear but were coming from the air, yet we were not able to see them at such a small level. His famous experiment was used with a curved neck placed on top of a beaker. This curved neck was the key to proving his findings because it showed that the germs and microbes had to fall into the broth inside. The curved neck did not allow this to happen.

The fermentation theory of disease is the (now obsolete) concept that many diseases, including the diseases which were "epidemic, endemic and contagious", owe their origin to the presence of a "morbific principle" in the system, acting in a manner analogous to, although not identical with, the process of fermentation. It was rendered obsolete by the germ theory of disease, which led to the new science of bacteriology.


Fermenting a broth in a beaker has become more than just a way to prove that organisms don't just appear out of thin air. Today, the process of fermentation is used for a multitude of everyday applications. Some of those processes include medications which we ingest, beverages we consume, and even food we eat. Currently, companies like Genencor International uses the production of enzymes involved in fermentation to build a revenue of over $400 million a year.[3] Many medications such as antibiotics are produced by the fermentation process. An example is the important drug cortisone, which can be prepared by the fermentation of a plant steroid known as diosgenin.

Burton Union fermentation system, Coors Visitor Centre

The enzymes used in the reaction are provided by the mold Rhizopus nigricans.[5] Just as it is commonly known, alcohol of all types and brands are also produced by way of fermentation and distillation. Moonshine is a classic example of how this is carried out. Finally, foods such as yogurt are made by fermentation processes as well. Yogurt is a fermented milk product that contains the characteristic bacterial cultures Lactobacillus bulgaricus and Streptococcus thermopiles.[6]

See also[edit]


  1. ^ Pasteur, Louis. "Physiological Theory of Fermentation". Fordham University. Retrieved March 13, 2014.
  2. ^ Fiachson, Refr. "Fermentation in Theory and Practice". Viking Food Guy. Retrieved March 13, 2014.
  3. ^ a b c Slonczewski, Joan (2009). Microbiology: An Evolving Science 2nd edition. New York: W.W. Norton.
  4. ^ Abbott, David. "Louis Pasteur". Retrieved March 30, 2014.
  5. ^ "Fermentation Uses".
  6. ^ "Milk Facts". Yogurt Production. Retrieved March 30, 2014.