Temperature and Alcohol-Related Problems

Lethal effects of a high fermentation temperature are often thought to result from the effect of temperature alone. However, inhibition is also the result of intracellular accumulations of ethanol. Temperature tolerance of yeast varies with species and strain and reflects intrinsic and extrinsic properties of the growth medium. Generally, yeast viability in alcoholic media subsides at temperatures near 35°C (95°F). 

The yeast cell membrane may be envisioned as a selectively permeable barrier that serves a vital role in the organism s ability to maintain osmotic balance and regulate transport of essential nutrients into and metabolites (including ethanol) out of the cell. Ethanol is soluble in both aqueous and lipid phases of the cell membrane and its formation and passive effusion eventually interferes with structure and function of the membrane. Particularly important in this regard are the cell-membrane-associated transport enzymes such as those responsible for uptake of sugars and critical amino acids. During active fermentation at warm temperatures, ethanol accumulates intracellularly faster than it can be eliminated from the cell. This situation worsens as extracellular concentrations increase. Thus, temperature- and ethanol-directed inhibition is likely the result of the time delay arising from passive diffusion coupled with impaired membrane function. 

Using the ratio of saturated (stearic to unsaturated (oleic 

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