Yeast Dry Debittered Brewer's
Yeasts are unicellular eukaryotic microorganisms classified in the kingdom Fungi. Approximately 1,500 species of yeasts have been described, most of which reproduce by budding, although in a few cases by binary fission. Yeasts measure about 3Âµm varying across species. The yeast species Saccharomyces cerevisiae has been used in baking and fermenting alcoholic beverages for thousands of years. It is also extremely important as a model organism in modern cell biology research, and is the most thoroughly researched eukaryotic microorganism, which gathers information into the biology of the eukaryotic cell and ultimately human biology. Other species of yeast, such as Candida albicans, are opportunistic pathogens and can cause infection in humans. Yeasts have recently been used to generate electricity in microbial fuel cells, and produce ethanol for the biofuel industry. Yeasts do not form a specific taxonomic or phylogenetic grouping. At present it is estimated that only 1% of all yeast species have been described.The term "yeast" is often taken as a synonym for S. cerevisiae,however the phylogenetic diversity of yeasts is shown by their placement in both divisions Ascomycota and Basidiomycota. The budding yeasts ("true yeasts") are classified in the order Saccharomycetales. Yeasts are chemoorganotrophs as they use organic compounds as a source of energy and do not require light to grow. The main source of carbon is obtained by hexose sugars such as glucose and fructose, or disaccharides such as sucrose and maltose, although some species can metabolise pentose sugars, alcohols, and organic acids. Yeast species either require oxygen for aerobic cellular respiration (obligate aerobes), or are anaerobic but also have aerobic methods of energy production (facultative anaerobes). Unlike bacteria, there are no known yeast species that grow anaerobically only (obligate anaerobes). Yeasts are ubiquitous in the environment, but are most frequently isolated from sugar-rich samples. Some good examples include fruits and berries (such as grapes, apples or peaches), and exudates from plants (such as plant saps or cacti). Some yeasts are found in association with soil and insects. Yeast are generally grown in the laboratory on solid growth media or liquid broths. Common media used for the cultivation of yeasts include; potato dextrose agar (PDA) or potato dextrose broth, Wallerstien Laboratories Nutrient agar (WLN), Yeast Peptone Dextrose agar (YPD), and Yeast Mould agar or broth (YM). The antibiotic cycloheximide is sometimes added to yeast growth media to inhibit the growth of Saccharomyces yeasts and select for wild/indigenous yeast species.