<P> Yeasts do not form a single taxonomic or phylogenetic grouping . The term "yeast" is often taken as a synonym for Saccharomyces cerevisiae, but the phylogenetic diversity of yeasts is shown by their placement in two separate phyla: the Ascomycota and the Basidiomycota . The budding yeasts ("true yeasts") are classified in the order Saccharomycetales, within the phylum Ascomycota . </P> <P> The word "yeast" comes from Old English gist, gyst, and from the Indo - European root yes -, meaning "boil", "foam", or "bubble". Yeast microbes are probably one of the earliest domesticated organisms . Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeast - raised bread, as well as drawings of 4,000 - year - old bakeries and breweries . In 1680, Dutch naturalist Anton van Leeuwenhoek first microscopically observed yeast, but at the time did not consider them to be living organisms, but rather globular structures . Researchers were doubtful whether yeasts were algae or fungi, but in 1837 Theodor Schwann recognized them as fungi . </P> <P> In 1857, French microbiologist Louis Pasteur proved in the paper "Mémoire sur la fermentation alcoolique" that alcoholic fermentation was conducted by living yeasts and not by a chemical catalyst . Pasteur showed that by bubbling oxygen into the yeast broth, cell growth could be increased, but fermentation was inhibited--an observation later called the "Pasteur effect". </P> <P> By the late 18th century, two yeast strains used in brewing had been identified: Saccharomyces cerevisiae (top - fermenting yeast) and S. carlsbergensis (bottom - fermenting yeast). S. cerevisiae has been sold commercially by the Dutch for bread - making since 1780; while, around 1800, the Germans started producing S. cerevisiae in the form of cream . In 1825, a method was developed to remove the liquid so the yeast could be prepared as solid blocks . The industrial production of yeast blocks was enhanced by the introduction of the filter press in 1867 . In 1872, Baron Max de Springer developed a manufacturing process to create granulated yeast, a technique that was used until the first World War . In the United States, naturally occurring airborne yeasts were used almost exclusively until commercial yeast was marketed at the Centennial Exposition in 1876 in Philadelphia, where Charles L. Fleischmann exhibited the product and a process to use it, as well as serving the resultant baked bread . </P>

Who discover the role of yeast in fermentation