He did this through his famous swan-neck flask experiment. Here's the gist:
* Pasteur boiled beef broth in swan-neck flasks, which had a long, curved neck that allowed air to enter but prevented dust and microorganisms from reaching the broth.
* The broth remained sterile for long periods, even when exposed to air.
* When he broke the neck of the flask, exposing the broth directly to the air, microorganisms grew in the broth within days.
This experiment proved that microorganisms in the air, not spontaneous generation, were responsible for the growth of organisms in the broth. It helped to definitively refute the theory of spontaneous generation, which had been widely accepted for centuries.
