Yeast is some unicellular fungi, not a unit of phylogenetic classification. Ascomycetes, Basidiomycetes and other single-celled fungi are the general names, which can be used for brewing production, some are pathogenic bacteria, and are model organisms for genetic engineering and cell cycle research. Yeast is the earliest microorganism used in the history of human civilization. Can survive in an anoxic environment. At present, there are more than 1000 kinds of yeasts. According to their ability to produce spores (ascospores and basidiomycetes), yeasts can be divided into three types: the strains that form spores belong to ascomycetes and basidiomycetes. Those that do not form spores but propagate mainly through budding are called incomplete fungi, or "pseudoyeasts" (yeast-like). At present, it is known that very few yeasts are classified into Ascomycetes. Yeast is widely distributed in nature, mainly growing in acidic, humid and sugary environment, and it is also very important in wine making. Yeast powder is that the yeast has not been decomposed, but the nutrients of yeast extract powder have been decomposed, so that the speed and efficiency of microbial absorption and utilization are higher and the fermentation residue is less; At present, the research of biological fermentation basically adopts yeast extract and yeast extract, and yeast powder is mainly used in traditional fermentation industries such as antibiotics.