(WHTM) — For six weeks, Louis Pasteur and Claude Bernard, both affiliated with the École Normale Supérieure, had been keeping watch over glass phials, some containing dog blood, some filled with dog urine. They were waiting to see if either would spoil.

People already knew food could keep longer if boiled. But long periods of boiling could also break down the flavors of food (not to mention make it really mushy). The question they were considering was, was it possible to prevent spoilage without bringing things to a boil?

The two scientists kept the phials at a steady temperature of 30 degrees Celsius (86 degrees Fahrenheit). On April 20, 1862, they opened the phials at a meeting of the French Academy of Sciences. (One wonders if the assembled scientists were holding their breath and prepared to bolt.) Neither the blood nor the urine had putrefied.

The experiment was a success, but Pasteur and Bernard disagreed on why. Bernard felt the heat prevented a chemical reaction, and Pasteur believed the heat killed off microbes. In a sense, both were right — the microbes initiated chemical reactions — but Pasteur was closer to the mark.

So, where best to use this process? Pasteur first tried it with wine. He demonstrated that if you heat wine to about 122-140 degrees Fahrenheit, the microbes would be killed, and the wine could then continue to age without losing quality.

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The process, which became known as “pasteurization,” was applied to a variety of foodstuffs. But it was when the process was applied to milk and milk products that it really became a major help to humanity. Raw milk can be very dangerous if not handled properly; the Centers for Disease Control and Prevention says it causes nearly three times more trips to the hospital for food-borne diseases than any other food. In the 1800s, before refrigeration, there was really no way to handle raw milk properly, at least by today’s standards.

With pasteurization, refrigerated milk can keep for two to three weeks. UHT (Ultra Heat Treated) milk in aseptic containers (commonly known as juice packs) can keep up to nine months, even without refrigeration. So pasteurization, with the help of refrigeration, has changed milk from one the most dangerous food items to one much safer. And Pasteur’s germ theory of disease is one of the bedrock principles of modern medicine.