There's a fine line between wine and vinegar. That's what Louis Pasteur discovered in 1856 when an alcohol manufacturer commissioned him to determine what was causing beet root alcohol to sour.

At that time, scientists thought that fermentation was a purely chemical process. Pasteur's research into fermentation led him to the discovery that it was yeast, a living organism, that turned the beet juice into alcohol. Under the microscope, yeast was round and plump. But when the alcohol spoiled, it contained a different microbe that was rod-shaped. Pasteur speculated that this rod-shaped microbe called Mycoderma aceti, which is commonly used to make vinegar, caused the wine to spoil [source: Feinstein].



These discoveries formed the "germ" of Pasteur's germ theory of fermentation. Years later, Pasteur would apply the same concepts to the origins of disease, leading to some of his greatest contributions to science and medicine.

In the meantime, Emperor Napoleon III enlisted Pasteur to save France's wine industry from the "diseases of wine" [source: Lewis]. In previous experiments, Pasteur had discovered that heating the fermented wine would kill the microbes that caused it to spoil. He wasn't the first to see that connection. Nicolas Appert, the inventor of in-container sterilization, also known as canning, had already shown that treating food with heat could preserve it. Pasteur's contribution was to determine the exact time and temperature that would kill the harmful microorganisms in the wine without changing its taste. He patented the process and called it pasteurization. Before long, the process was also used for beer and vinegar.

The pasteurization of milk didn't come into practice until the late 1800s. Back then, tuberculosis was commonly carried by milk. A low-temperature, long-time (LTLT) process, also known as batch pasteurization, was first developed to kill the tuberculosis pathogen. The incidence of tuberculosis contracted from milk fell dramatically, and in fact it no longer makes the Centers for Disease Control and Prevention's list of foodborne illnesses [source: CDC ].

The first commercial milk pasteurizers were produced in 1882, using a high-temperature, short-time (HTST) process. The first law to require the pasteurization of milk was passed in Chicago in 1908 [source: Sun]. Some people didn't like the idea of pasteurizing milk in the beginning, for many of the same reasons that today's raw milk advocates cite [source: Lewis]. We'll talk more later about raw milk and why some people love it and some people hate it.