The first step in the manufacture of vinegar, as noted earlier, is the production of an ethanolic substrate. For the most part, the relevant fermentations (i.e., wine and beer) are discussed separately (Chapters 9 and 10). However, it is worth noting that ethanol from musts, ciders, or malt mashes are usually prepared with the eventual end product (i.e., vinegar) in mind. Thus, the starting materials do not necessarily have to be of the highest quality. However, this does not mean that poor quality materials should be used, since many of the flavor and aroma properties of the finished vinegar are derived from the starting material. Of course, if distilled ethanol is used as the substrate, then the resulting vinegar will lack most of these flavor and aroma characteristics.
The second step of vinegar production, conversion of ethanol substrate to acetic acid, can be performed by one of several methods, all of which rely on oxidative fermentation of ethanol by acetic acid bacteria.These processes are generally referred to as the open vat method, the trickling generator process, and the submerged fermentation process. The latter two are now the more widely used, especially for larger vinegar manufacturers, since they can be performed in continuous mode and can reduce the fermentation time from several weeks to a matter of days. However, even the traditional open vat method can be run in a semi-continuous fashion and is still used in many parts of the world. Moreover, the open vat process is the method of choice for the premium types of vinegar, including various wine vinegars, such as Balsamic (Box 11-2).
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