most yeasts used industrially are i

most yeasts used industrially are int the genus saccharomyces. the term wild yeast' is applied to any yeast other than the one being used or encouraged. thus a yeast employed in one process could be a wild yeast in another.most of the troublesome wild yeasts are asporogenous,or false,yeasts.

Genus Schizosaccharomyces These yeasts,which reproduce asexually by fission and form four or eight ascospores per ascus after isogamic conjugation,have been found in tropical fruits,molasses,soil,honey,and elsewhere. A common species is S.pombe.

Genus Saccharomyces Cells of these yeasts may be round,ovate,or elongated and may form a pseudomycelium.Reproduction is by multipolar budding or by ascospore formation,which may follow conjugation or may develop form diploid cells when these represent the vegetative stage.The ascospore,one to four per ascus,are usually round or ovate.The leading species, S.cerevisiae, is employed in many food industries, with special strains used for the leavening of bread, as top yeasts for ale, for wines, and for the production of alcohol, glycerol, and invertase. top yeasts are very active fermenters and grow rapidly at 20 C. The clumping of the cells and the rapid evolution of CO2 sweep the cells to the surface,hence the term top yeast. Bottom yeast do not clump,grow more slowly,and are best fermenters at lower temperatures(10to15C).The absence of clumping and the slower growth and evolution of CO2 permit the yeast to settle to the bottom,hence the term bottom yeast. These characteristics of brewers'yeast are observations and do not explain why some yeast clump,or flocculate. A detailed discussion on the theories regarding the flocculation of brewers'yeasts can be found in Rose and Harrison(1970)

S.cerevisiae var. ellipsoideus is a high-alcohol-yielding variety used to produce industrial alcohol,wines,and distilled liquors.S.uvarum, a bottom yeast, is used in making beer.S.fragilis and S.lactis,because of their ability to ferment lactose,may be important in milk or milk
products.S.rouxii and S.mellis are osmophilic.

According to Lodder(1984),many of the Saccharomyces have been reclassified.for example,S.cerevisiae,S.fragilis is now Kluyveromyces marxianus,and S.lactis is now K.marxianus Var.lactis.S.rouxii,S.mellis,and S.nussbaumeri are now Zygosaccharomyces rouxii.Debaryomyces kloeckeri is now D.hansenii.