Saccharomyces pastorianus is a species of yeast commonly used in brewing and baking. It is a bottom-fermenting yeast, meaning it ferments at cooler temperatures and settles at the bottom of fermentation vessels. This characteristic makes it ideal for producing lagers, a type of beer that is known for its crisp and clean flavor. This yeast was first identified in the late 19th century and is named after the French scientist Louis Pasteur, who studied fermentation processes. Saccharomyces pastorianus plays a crucial role in the brewing industry, contributing to the production of various beer styles around the world.