In one of its most common forms, vinegar has been used as a preservative since ancient times.
Vinegar can be made from any liquid that is capable of being converted into alcohol in a two stage process. During fermentation the sugar in the liquid is converted into alcohol and carbon dioxide gas by the actions of yeast enzymes. Then, the alcohol combines with atmospheric oxygen by the action of the Acetobacter bacteria, forming acetic acid and water.
It is because of the variety of source materials, and the differing organic acids and esters derived from that source material which are also present, that are responsible for the different flavours and aromas of vinegar, for example, grapes - wine vinegar, apples - cider vinegar, malted barley or oats - malt vinegar.
In addition to the method for producing vinegar, large amounts of acetic acid are prepared synthetically either by acetylene being hydrated to acetaldehyde, which is then oxidized or by a process using methanol, from gas or oil, and carbon monoxide.
In foods it is used for its antibacterial properties, as an acidity stabiliser, diluting colourings, as a flavouring agent and for inhibiting mould growth in bread. In brewing it is used to reduce excess losses of carbohydrate from the germinated barley and to compensate for production variations, so producing a consistent quality beer.
It can be found in beer, bread, cheese, chutney, horseradish cream, pickles, salad cream, brown sauce, fruit sauce, mint sauce and jelly and tinned baby food, sardines and tomatoes.
Occurring naturally in body fluids and plant juices acetic acid, also called ethanoic acid, is the most important of the carboxylic acids. It is an important metabolic intermediate being involved in fatty acid and carbohydrate metabolism.