Question

Yeast poisons themselves to death when alcohol concentration reaches to in alcoholic fermentation. (a) \(2 \%\) (b) \(10 \%\) (c) \(13 \%\) (d) \(20 \%\)

Short answer

(c) \( 13 \% \)

Step-by-step solution

Understand the Process of Alcoholic Fermentation

Alcoholic fermentation is a process where yeast cells consume sugar and produce ethanol (alcohol) and carbon dioxide as waste. This process is self-limiting as the yeast cells start to die when the alcohol concentration in their environment is too high.

Determine the Threshhold of Alcohol Concentration

The alcohol concentration threshold at which yeast poisons themselves to death is a specific scientific data based on several research studies. According to most studies, yeast cells start to die off if the alcohol concentration in their environment reaches \(13 \% \). Therefore, 13% is the threshold.

Key concepts

Yeast Metabolism

Yeast is a type of fungus that plays a crucial role in the process of alcoholic fermentation. It is fascinating because of its ability to convert sugars into ethanol and carbon dioxide, a process known as yeast metabolism. When yeast cells come into contact with sugar, they begin a series of chemical reactions.

• Firstly, yeast breaks down glucose through glycolysis to produce pyruvate.
• Then, in the absence of oxygen, pyruvate is converted to ethanol and carbon dioxide. This process liberates energy, which the yeast uses for growth and reproduction.

Ultimately, this transformation enables the production of alcoholic beverages as well as leavened bread. The efficiency of yeast metabolism heavily depends on the environmental conditions such as temperature, pH, and nutrient availability.

Understanding yeast metabolism is essential to control the fermentation process effectively, ensuring the desired level of alcohol while maintaining yeast vitality.

Ethanol Toxicity

Ethanol, which is the type of alcohol produced during fermentation, can become toxic. For yeast, it is both a product and a poison.

As the concentration of ethanol increases during fermentation, it can damage the cell membranes and other cellular structures of yeast. This happens because ethanol has a dehydrating effect, drawing out water from cells and disrupting normal cellular functions.

• High ethanol levels can lead to lipid peroxidation, damaging cell membranes.
• It can also denature essential proteins, affecting the yeast's ability to function properly.

Yeast cells have some mechanisms to tolerate ethanol, like altering their membrane compositions to become less permeable to ethanol, but beyond a certain point, these mechanisms fail. Generally, once ethanol concentration reaches a critical level, such as 13%, yeast cells begin to die due to ethanol toxicity.

Fermentation Threshold

The concept of fermentation threshold is crucial in understanding why yeast ultimately ceases to produce alcohol. It refers to the maximum concentration of ethanol that yeast can tolerate before its metabolic processes are inhibited or halted altogether.

This threshold is typically around 13%, as yeast metabolism slows and eventually stops when alcohol concentrations reach this level.

• Fermentation threshold varies with different strains of yeast. Some strains might have higher tolerance levels and can achieve greater ethanol concentrations.
• Brewers and winemakers often select specific yeast strains for this reason, aligning the desired alcohol content with the yeast's fermentation threshold.

Crossing the fermentation threshold means that the yeast is overwhelmed by the ethanol it has produced, which not only stops further ethanol production but also leads to cell death. Therefore, understanding the fermentation threshold helps in predicting the cessation of fermentation and planning the fermentation process effectively.