Final answer:
1. Louis Pasteur discovered that bacteria was the cause of 'souring' of wine by studying the causes of beer and wine spoilage in 1856.
Step-by-step explanation:
The correct answer is 1. Louis Pasteur. While studying the causes of beer and wine spoilage in 1856, Pasteur discovered properties of fermentation by microorganisms.
He demonstrated that airborne microbes, not spontaneous generation, were the cause of food spoilage, and he suggested that if microbes were responsible for food spoilage and fermentation, they could also be responsible for causing infection. This discovery laid the foundation for the germ theory of disease.