Louis Pasteur is the scientist who discovered fermentation.

Louis Pasteur:
Louis Pasteur was a French chemist and microbiologist who made significant contributions to various fields of science, including fermentation, immunization, and pasteurization. He is widely regarded as one of the greatest scientists in history.

Discovery of Fermentation:
Fermentation is a metabolic process in which microorganisms, such as yeast or bacteria, convert sugars into alcohol or acids. It has been used for centuries in the production of various food and beverages, such as bread, beer, and wine. However, the exact nature of fermentation and the role of microorganisms involved were not well understood until Louis Pasteur's groundbreaking experiments.

Spontaneous Generation:
During Pasteur's time, there was a prevalent belief in the theory of spontaneous generation, which suggested that living organisms could arise spontaneously from non-living matter. Pasteur aimed to disprove this theory and demonstrate that microorganisms responsible for fermentation and decay came from pre-existing microorganisms.

Swan-neck Flask Experiment:
Pasteur designed a series of experiments to test the theory of spontaneous generation. In one of his most famous experiments, he used swan-neck flasks. These flasks had a long curved neck that allowed air to enter but prevented dust particles and microorganisms from reaching the liquid inside. Pasteur boiled the liquid in the flask to kill any existing microorganisms and then observed that no fermentation or decay occurred as long as the flask remained intact. However, when the flask was tilted or broken, allowing the entrance of airborne microorganisms, fermentation and decay quickly took place.

Conclusion:
From these experiments, Pasteur concluded that fermentation and decay were caused by microorganisms present in the air, not by spontaneous generation. This discovery revolutionized the field of microbiology and had practical applications in the food and beverage industry. Pasteur's work laid the foundation for the development of modern microbiology and our understanding of fermentation processes.