The production of vinegar is based on the transformation of alcohol to acetic acid. This transformation occurs under the influence of acetic bacteria first discovered by Pasteur. It is also produced from grape must according to traditional recipes and so the alcoholic fermentation and the acetification (transformation of alcohol to acetic acid happen simultaneously.
The traditional method of making vinegar is a slow process, during which the wine or grape must, after having been mixed with a quantity of high quality old quality vinegar; it is left in semi filled barrels. This mixture, with the help of oxygen and with the action of acetic bacteria, is slowly acetified over a period of many months. The industrialized method was discovered later. The industrialised method of acetification happens very quickly, in huge reactors, under pressure of hot air. Here the reaction is mainly chemical and not biological. It is obvious that the traditional method of making vinegar produces a far superior quality product to the industrialized method.
The quality of traditional vinegar is completed during the ageing process in oak and chestnut barrels and barrels made of and other types of wood. The aging process is necessary because, in its immature state, vinegar has a harsh taste.
The aging process enriches the flavours of vinegar and softens it. During this process, with the help of controlled oxygen seeping through the pores of the wooden barrels, a series of reactions occur similar to those which happen during the ageing process of wine. These reactions provoke a series of changes in the colour, flavour and taste of the vinegar.
Through ageing vinegar takes on brownish shades of colour whilst the violet hue in fresh, red vinegar and the greenish hue in white vinegar are reduced and finally disappear. The aroma is strengthened and becomes more complex. With ageing the taste softens and becomes fuller and more bodied.