How Did Louis Pasteur’s Germ Theory Originate and How Did He Discover the Process of Pasteurization?
It was known in Pasteur’s time that yeast cells cause fermentation, but it was believed that it was their death and decomposition that caused the necessary chemical reaction.
Pasteur had a new theory: fermentation is caused by the action of living cells, not their decomposition. He believed these living things reproduce; they do not simply appear.
To prove his theory, Pasteur studied the organisms of many different ferments, wine, vinegar, milk, beer, under his microscope.
The results were conclusive: the microbes could live without air by extracting energy from the organic substance around it.
For example, yeast changes the sugar in grapes to alcohol.
Microorganisms in milk change the sugar in milk, lactose, into lactic acid, and the milk sours. Pasteur said that germs are everywhere and that the effect they have on our lives is often very dangerous.
The science of microbiology was born.
Now that the process of fermentation was understood, it could be controlled.
The wine industry asked Pasteur to study why some of their wine spoiled and some did not. Under his microscope, he studied the yeast cells from good wine and bad wine, and found different shapes between the two.
He discovered that once the wine is formed, heat is the solution. If wine is heated to about 120°F, all the remaining yeast is killed and the wine will not spoil. The same process was applied to milk to keep it from souring and came to be known as pasteurization in his name.
Pasteur also saved France’s silk industry by uncovering a parasite that was destroying the silkworms, but he was just beginning.
His discovery of the effects of microbes led him to his germ theory of disease: microorganisms also cause disease in animals and humans. These diseases are therefore infectious because the germs can be carried from one person to another.
It was in proving his germ theory that Pasteur, more than any other scientist, probably had the most profound effect on human beings.