Question

This question is from my Microbiology lab manual pertaining to an experiment dealing with Carbohydrate Fermentation.

For a special occassion you open a 20-year-old bottle of red wine. You are excited. But after the first sip you are shocked: the wine tastes like vinegar. Is this possible? If yes or no, give a detailed explanation!

Answer 1

Yes, it is quite possible.

Probably, attack of the acetic acid bacteria which thrive in wineries, on winery equipment and in the air. Acetic acid bacteria carry out aerobic respiration, and oxygen is generally used as the final electron acceptor; however, other compounds may occasionally act as final electron acceptors, allowing the bacteria to survive under nearly anaerobic conditions, such as the ones present during wine fermentation. The bacteria can metabolise some acetic acid by tricarboxylic acid cycle function, enabling them to completely transform acetic acid to CO2 and water. However, because entry into the acetate cycle is inhibited by the presence of ethanol, it is essential to maintain a low concentration of ethanol in the presence of acetic acid bacteria to prevent this full oxidation. In fact, ethanol concentrations between 0.5 and 1% are regularly maintained in vinegars. When these bacteria come in contact with wine and oxygen, they tend to produce acetic acid, the stuff that makes vinegary smell and taste.