A Key Figure in Food Safety

“It’s hard to say if the medical studies or the food work came first,” said Dr. Vasavada. “What causes spoilage? What causes infections? Before Pasteur, it was explained by spontaneous generation. But we would not be where we are in terms of food quality if we did not have Pasteur. He had vision and was ahead of his time.”

Pasteur held public experiments at the University of Paris to show that bacteria caused spoilage, according to a November 1956 article published in Engineering and Science magazine titled “The Origin of Life: A colorful account of the studies man has made in his attempt to discover the fundamental characteristics of living matter,” by Norman H. Horowitz, a Caltech geneticist.

In the first of the three experiments, Pasteur showed that boiling and destroying bacteria in a flask and then letting only sterile air enter it resulted in no bacterial growth. The second experiment showed that bacteria would grow in a medium exposed to dust from the air. The third experiment, perhaps his most famous, used the gooseneck flasks he had invented. For the test, he prepared broth in a regular flask that he had in a flame, from which he pulled it to create a thin gooseneck. He boiled the medium in the flask for several minutes until steam rose in the gooseneck. He then put that flask into an incubator without sealing it and showed that nothing would grow in it.

According to Horowitz, Pasteur explained that when the broth is boiled, the steam rising through the gooseneck drives the air out. When the flame is then turned off, air does come back into the flask, but it is exposed to liquid almost at its boiling point, which can kill the bacteria. As the broth cools, less air comes into the flask because it is trapped in the moist gooseneck, so it never reaches the cool broth. Horowitz noted that the experiments showed that bacteria were not spontaneously generated, as had previously been believed.

“What he did goes to the crux of food spoilage,” said Dr. Vasavada.

Valigra is a freelance writer based in Cambridge, Mass. Reach her at [email protected].