People have used yeast for fermentation and baking throughout history. Only in the last 150 years, since the experiments of Louis Pasteur, have scientist begun to explore how yeast works. Pasteur first proposed the production of carbon dioxide from yeast as responsible for raising a loaf of bread in 1859. Wild yeast spores are constantly floating in the air and landing on uncovered foods and liquids. These wild varieties contributed some of the earliest kinds of sourdough bread mixes which did not depend on adding starter cultures.
Yeast is also a popular organism for studying genetics.
Baker's yeast is one of only a half-dozen microbes on Earth whose unique gene script has recently been comprehensively deciphered. Notable in the yeast gene is a host of signals that trigger the microbe to protect itself against extremes in cold and heat, called thermal shock proteins. Hopes now run high in the biological community that over the next several years, more than 50 to 100 additional microbes will also provide comprehensive genetic scripts for their lifecycles, including how these organisms might survive under relentless swings in near boiling water, deep ice, or even in the core of an active volcano vent and nuclear reactors. When yeast are supplied with both sugar and oxygen, the colonies grow up to 20 times faster through cell division than without oxygen. The great medical microbiologist, Louis Pasteur, played a central role in proving this conversion to ethanol required living organisms, rather than a chemical catalyst.