In 1857, who was the first to experimentally demonstrate that the yeast responsible for making alcohol from sugar, and contaminating microorganisms found in normal air, could sour fermentation?

Louis Pasteur

The correct answer is Option (2) - Louis Pasteur

Louis Pasteur, a French chemist and microbiologist, was the first to experimentally demonstrate that yeast, responsible for fermenting sugar into alcohol, could be affected by contaminating microorganisms present in the air. Through his meticulous experiments in the mid-19th century, Pasteur showed that the process of fermentation could be controlled and improved by preventing the introduction of these unwanted microorganisms. His discoveries laid the foundation for modern microbiology and paved the way for advancements in fermentation processes, including those used in the production of alcoholic beverages and various other industries.