Ethanol yeasts

Bakers Yeast Production. Bakers yeast is grown aerobicaHy in fed-batch fermentors under conditions of carbohydrate limitation. This maximizes the yield of yeast biomass and minimizes the production of ethanol. Yeasts grown under these conditions have exceUent dough leavening capabHity and perform much better in the bakery than yeast grown under anaerobic conditions. 

Many foods such as alcohoHc beverages, pickles, cheese, and fish sauce are preserved by fermentation. Spontaneous fermentations by mixed populations of yeasts and bacteria are normally iavolved. Preservation results from a lowering of pH or the formation of ethanol. Yeasts do not produce antibiotics, although isolates of a number of species produce a toxia ("killer factor") lethal to other yeasts. 

Glycerol is the third most abundant component of wine after water and ethanol. Yeasts use it as a carbon source and reduce its concentration with time. This has prompted the use of the glycerol content of wine as a measure of its degree of aging (Cortes et al. 1998 Moreno et al. 2001). 

Molasses. Molasses is the final effluent obtained in the preparation of sugar by repeated crystallization. The sugar it contains cannot be removed economically. The molasses from cane sugar is most commonly known as blackstrap and that from beet is called beet molasses. Molasses is mainly used for the manufacture of ethyl alcohol (ethanol), yeast, and cattle feed. Another use of sweet molasses is in cooking, spreads for bread, topping for pancakes, and in the manufacture of alcoholic beverages. 

B14 Ethanol production in a three-phase Ethanol Yeast Energy, commodity [28]... 

In choosing a yeast strain, the yeasts should certainly be resistant to ethanol. Yeasts commercialized under the name S. bayanus could be recommended but they seem to have a propensity to form volatile acidity in these conditions. Commercially available S. cerevisiae yeasts (formerly S. bayanus), known for their resistance to ethanol and low probability of producing volatile acidity, are recommended for this purpose. 

Graves, T, Narendranath, N., Power, R. Development of a Stress Model fermentation system for fuel ethanol yeast strains. J Inst Brew. 2007, 113,263-271. 

Guo, Z., Zhang, L., Ding, Z., Shi, G. Minimization of glycerol synthesis in industrial ethanol yeast without influencing its fermentation performance. Metab Eng. 2011,13,49-59. 

Stambuk, B. U., Dunn, B., Alves, S. L., Duval, E. H., Sherlock, G. Industrial fuel ethanol yeasts contain adaptive copy number changes in genes involved in vitamin B1 and B6 biosynthesis. Genome Res. 2009, 19,2211-221%. 

More advanced organisms, like yeasts, can use thiamine diphosphate with different enzymes to oxidize glucose to ethanol and carbon dioxide (Figure 2.13). The NADH produced in the glucose break-down is then used to reduce acetaldehyde to ethanol. Yeast is therefore used by the brewer for the alcohol produced and by the baker for the CO2 to aerate the bread. 

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