Louis Pasteur (1822–1895) is widely considered the father of
microbiology for his pioneering work on fermentation, microscopy,
vaccination, and bacteriology. A chemist (and not a physician), Pasteur
was one of the first scientists to put the microscope to work for the good
of mankind. An early publication in 1855, a study of the formation of
lactic acid in the souring of milk, included the observation of “budding
organisms” that he guessed were the active causes of fermentation, similar
to the “tiny self-replicating organisms” associated with alcoholic
fermentation.^22 At the time of the career-organizing publication, Pasteur
was the new dean of sciences at Lille University (on the French-Belgian
border), and was approached by a local manufacturer of beet-root alcohol
who told the chemist of a mysterious catastrophe that was threatening the
local beer and wine industries.
Pasteur, the new man in Lille, listened to the story of the “slimy juice of
useless sour ooze”^23 and instead of resorting to chemical experimentation,
turned to microscopic examination. Perhaps the brewer had heard of
Pasteur’s previous souring-milk publication, but there simply did not exist
in the world a bacteriologist. Professor Pasteur gathered samples of the
spoiled beet-root alcohol, placed droplets on a glass slide, and, adjusting
the little mirror of his microscope to pinpoint the sunlight onto the
morass, envisaged a peculiar partnership. There in the liquid were tiny
yeast bodies, buoyantly adrift potatoes in the slurry, and what had been
conjecture a year before, Pasteur now petitioned with confidence: the yeast
organisms were the agents of fermentation.
Fermentation of sugars (found in beets, grapes, wheat, potatoes, corn,
rice, and even bananas) by naturally occurring yeast has unwittingly been
mankind’s test kitchen for purification of liquid, making it intoxicatingly
potable. Pasteur had unraveled the conundrum and for good measure,
made another stunning observation: also present in the soured batches
were great numbers of rod-shaped microbes. These, he reasoned, were the
germs that were causing the spoilage. What earlier explorers had
postulated might be operating organically, Pasteur now was
demonstrating: the collaboration between the yeast and the sugars cloaked
inside the fruits and grains was fermentation, while the interaction
between bacteria and the sugars evidenced rotten slime. Fermentation
good, putrefaction bad.