Explain the production of vinegar with the help of microbes.

Answer: Vinegar is a dilute solution (about 4%) of acetic acid. It is made from sugary raw material by two fermentations carried out by microbes.

1. Raw material: fruit juice (grapes, apples) or sugarcane molasses, which contain sugar.
2. Alcoholic fermentation: yeast (Saccharomyces cerevisiae) is added. In the absence of air it converts the sugar into ethyl alcohol and carbon dioxide.
3. Acetic acid fermentation: the alcohol is then exposed to air and the bacterium Acetobacter aceti is added. It oxidises the ethyl alcohol into acetic acid. The liquid is filtered and packed as vinegar.

Vinegar is used to preserve food (pickles, sauces) and to give a sour taste.