The alcohol concentration beyond which yeast cells cannot survive and fermentation ceases is approximately how much?

The correct option is 0.13.

Explanation

Alcoholic fermentation is an anaerobic process carried out by yeast (specifically Saccharomyces cerevisiae), wherein sugars are converted into ethanol and carbon dioxide. While ethanol is the desired product for industrial applications, it acts as a toxic metabolite for the yeast cells themselves.

Detailed Analysis:

• During fermentation, as the concentration of alcohol increases in the medium, it begins to inhibit the metabolic activities of the yeast.
• Yeast cells generally cannot withstand an alcohol concentration beyond approximately 13%. At this level, the ethanol becomes lethal to the cells, causing them to die ("poison themselves to death").
• Consequently, the fermentation process ceases naturally at this concentration.
• To obtain alcoholic beverages with a concentration higher than 13% (such as whisky, brandy, or rum), the fermented broth must undergo distillation.

Key Takeaway:
Natural fermentation is self-limiting because yeast cells die due to alcohol toxicity when the concentration reaches approximately 13%.