Louis Pasteur: The Story of Pasteurization

Have you ever seen the word “pasteurized” on a carton of milk?  It might evoke images of idyllic pastures where cows roam freely, but in reality, it's all about the process that milk undergoes after it's been collected from the cow.

Before milk goes into cartons and sold in supermarkets, it undergoes pasteurization. The milk is heated to a specific temperature to kill any harmful microorganisms, or germs that can make you sick. The process is named after the brilliant scientist Louis Pasteur who pioneered this revolutionary process.

Louis Pasteur's Educational Background

Born in 1822 in Dole, France, Louis came from a long line of leather tanners. His family was poor, and as a child, Louis wasn’t interested in school. He preferred fishing and drawing. However, things changed when Louis went off to college. He began to study hard but still struggled. His grades in chemistry (a subject he would later do important work in) were especially bad. He wanted to go to the prestigious Ecole Normale Superieure in Paris, but had to take the entrance exam twice! But even though he had setbacks, his hard work and dedication paid off. 

While he was working to try to get into the Ecole Normale, Louis began attending lectures by a famous chemist and decided that he wanted to be a chemist too. So, when he finally got accepted into the Ecole Normale, he decided to study chemistry. After he got his doctoral degree, he got a job at the University of Strasbourg, teaching and doing research in the structure of chemical crystals. 

Louis Pasteur’s Early Works

Even though Louis began as a chemist, his most important work is in microbiology, the study of organisms so small that you need a microscope to see them. This shift happened almost by accident, but as Louis himself reminded people, “In the fields of observation, chance favours the prepared mind.”

In 1854, he got a new job at a university in northern France. While there, the owner of a factory came to him with a problem. His factory fermented sugar beets to make alcohol, but sometimes he ended up with a spoiled, sour elixir, instead of alcohol.  At that time, scientists didn’t know how fermentation worked. Some thought it was just chemicals rearranging themselves spontaneously under the right conditions. Most people just knew that when you left crushed grapes or soggy grain in a covered container for long enough, you got wine or beer. Louis wasn’t satisfied with those answers though, and set about trying to solve the mystery. He got samples of the good alcohol and the sour substance and put them under his microscope. 

During his investigations he noticed that different kinds of microorganisms swimming around in them! The alcohol samples had yeast, which is a microscopic type of fungus. The sour stuff had bacteria, which is a completely different kind of microorganism! Both types float around in the air, but Louis was the first to realize that the yeast settled in containers of grapes or mashed grain and caused fermentation. Those tiny yeast ate up the sugars in the beets, used it to make energy, and then got rid of the waste that they didn’t need. That waste was the alcohol.

Studies in Microorganisms

Louis was now determined to study this phenomenon further. He went on to study the microorganisms in wine and beer, finding new ways to make sure they weren’t contaminated by tiny organisms that would spoil them. But he wasn’t just interested in making beverages safer, although this was very important for people’s health and the French economy. Louis wanted to know more about how these tiny microorganisms lived. If so many scientists were wrong about fermentation, what other discoveries were waiting to be made?

One idea that didn’t make much sense to Louis was “spontaneous generation.” Spontaneous generation was the idea that some living creatures just arose from nonliving things. Rotting meat made flies, some people thought, because they’d seen fly larvae on rotting meat. Louis thought that flies must be laying tiny eggs in the meat. He suspected that microorganisms, like the yeast in beer and wine, actually float around in the air, settling on things and, if the conditions are right, growing and multiplying.

Louis invented an ingenious way to demonstrate that living things didn’t just spring fully-formed from non-living things. He designed a bottle with a long, skinny neck that curved downward like the top of the letter S, opening toward the ground. He then boiled a broth, killing any microorganisms that were already in it. He poured some of the broth into the S-neck bottles, and some into bottles with necks that opened upwards, toward the sky. 

Then he waited. After a few weeks, the bottles with the S-necks hadn’t changed. But the ones with upward-facing necks had become cloudy. Looking at the liquid under a microscope confirmed that microorganisms had landed from the air and grown in it. But, microorganisms couldn’t land in the S-neck bottles, so that liquid stayed clear!

The Science Behind Pasteurization

At its core, pasteurization relies on heat to destroy harmful bacteria in milk. By heating milk to temperatures ranging from 145 to 212 degrees Fahrenheit (63 to 100 degrees Celsius) for a specific duration, pasteurization effectively eliminates pathogens like Salmonella, E. coli, and Listeria, ensuring the safety of dairy products for consumers. In addition to milk, pasteurization is also used to treat other beverages like fruit juices, beer, and wine, as well as certain food products like honey and eggs.

The Impact of Pasteurization

Pasteurization has revolutionized the dairy industry and significantly reduced the risk of foodborne illnesses associated with consuming raw milk. By ensuring the safety and quality of dairy products, pasteurization has played a crucial role in safeguarding public health and improving food hygiene standards worldwide.

As we raise a glass of pasteurized milk or enjoy other dairy products, let's take a moment to appreciate the scientific ingenuity and dedication that went into making them safe for consumption. Thanks to the pioneering work of Louis Pasteur and the widespread adoption of pasteurization, we can indulge in our favourite dairy delights with confidence, knowing that they're not only delicious but also safe and wholesome.