Question

For acetic acid fermentation, the alcohol content of the fermented liquid is adjusted to

• A. 3-4 %
• B. 7-8 %
• C. 10-13 %
• D. 13-15 %

Hint:

Adjusting alcohol to $7\text{--}8\%$ prevents substrate inhibition of Acetobacter and yields $6\text{--}7\%$ commercial vinegar.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Industrial vinegar manufacture involves a two-stage fermentation: primary anaerobic alcoholic fermentation followed by aerobic acetic acid oxidation.

Step 2: Detailed Explanation:
In the acetic acid oxidation stage, Acetobacter aceti oxidizes ethanol into acetic acid:
\[\text{CH}_3\text{CH}_2\text{OH} + \text{O}_2 \xrightarrow{\text{Acetobacter}} \text{CH}_3\text{COOH} + \text{H}_2\text{O}\] Ethanol concentrations above $10\text{--}12\%$ severely inhibit Acetobacter dehydrogenase activity, while concentrations below $5\%$ risk complete over-oxidation into $\text{CO}_2$ and $\text{H}_2\text{O}$.
Thus, the alcoholic feedstock is diluted and adjusted to an optimal $7\text{--}8\%$ ethanol concentration.

Step 3: Final Answer:
Hence, the alcohol content is adjusted to 7-8%.