Yeast, baker bottom

Top yeast = baker s yeast bottom yeast = brewer s yeast. 

NOTE Literature is not always clear on name of species top or bottom yeast, bakers, brewers or impoverished yeast, nor is it certain that ail were strains of cerevisiae. Wherever possible the original source and type are given. Note on Reactions Attributed to Yeast In the years 1937-1938 many oxidations of steroids were erroneously reported to be car -ried out by yeast (see Ref. V-1047). Later work showed that these reactions were due to species of corynebacteria and flavobacteria which were contaminants in the yeast preparations (see Ref. A-17). A-17 K-457 M-552 M-594 V-1047... 

Properties of Pentahydrate, M.p. 80°C. [a] +105.2° (c, 4 water). Partially fermented by top yeast (bakers yeast) with formation of melibiose completely fermented by bottom yeast. Nonreducing. 

A 4-L, three-necked, round-bottomed flask equipped with mechanical stirrer, bubble counter, and a stopper is charged with 1.6 L tap water, 300 g of sucrose (Note 1), and 200 g baker s yeast (Note 2), which are added with stirring in this order. The mixture is stirred for 1 hr at about 30°C, 20.0 g (0.154 mol) of ethyl acetoacetate (Note 3) are added, and the fermenting suspension (Note 4) is stirred for another 24 hr at room temperature. A warm (ca. 40°C) solution of 200 g sucrose (Note 1) in 1 L of tap water is then added, followed 1 hr later by an additional 20.0 g (0.154 mol) of ethyl acetoacetate (Note 3). Stirring is continued for 50-60 hr at room temperature. When the reaction is complete by gas chromatographic analysis... 

Conditions To a 500-mL round-bottom flask are added 110 mL of tap H,0, 7 g of pressed baker s yeast... 

A great deal of attention has been directed to the anaerobic fermentation by yeasts, notably Saccharomyces cerevisiae in its various forms (top and bottom brewers and bakers yeast). This has been industrially important, and the subspherical cells, about 6-8 /n in diameter, are produced under standard conditions. They can be brought into suspension with little or no clumping. They are then suitable for tests of the permeation through the surface of the suspended cells. From the discussion on pages 9-13, it follows that permeation can be treated either as the diffusion into spheres, where there is no semipermeable plasma membrane, or as the unidimensional diffusion through a relatively thin, slightly permeable membrane, with substantial complete diffusion of permeant. Since there is every reason to assume the latter case, the former case is considered unimportant. 

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