In the late 1850s, Pasteur was employed by a brewing company who wanted him to figure out why their beer was going sour
Using powerful new microscopes, pasteur found it was tiny organisms causing the alcohol to go sour. To prove this, he sealed the alcohol and it didn't go sour. He also discovered that these tiny organisms were killed when heated
Pasteur published his germ theory in 1861
By 1865 pasteur had also proved microbes were causing silk worms to die
