if any, is quite variable depending on the wine in question, the storage time, and the temperature. The intensity of this phenomenon is rather random. Exposure to low temperatures actually seems to increase the magnitude of the problem. Studies are currently being conducted to understand the origins of observed haze problems and to establish the optimal conditions of use.
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CHAPTER 2 Alcohols and Other Volatile Compounds
2.1 Ethanol
Besides water, ethanol (ethyl alcohol) is the most plentiful compound in wine. A wine's strength is expressed in terms of alcohol content or the percentage of alcohol by volume. As ethanol has a specific gravity of 0.79, a wine with an alcohol content of 10% vol. contains 79 g/l of ethanol by weight. The alcohol content of wine, expressed in terms of density, is generally 100 g/l (12.6% vol.), although it may exceptionally be as high as 136 g/l (e.g. an alcohol content of 16% vol.).
Due to the low specific gravity of ethanol, dry wines, containing negligible amounts of residual sugar, have specific gravities below that of water (1.00), ranging from 0.91 to 0.94. This value decreases as the alcohol content increases.
Ethanol in wine is mainly produced by the alcoholic fermentation of sugar in must. However, grape cells are also capable of forming small quantities, mainly under anaerobic conditions (carbonic maceration; see Volume 1, Section 12.9.3). The appearance of traces of ethanol in grapes results from alcohol dehydrogenase activity, which acts as a marker for ripeness.
As approximately 16–18 g/l of sugar is required to produce 1% vol. of ethanol during alcoholic fermentation, grape must has to contain 180, 226, and 288 g/l of sugar to produce wines with 10, 12.6, and 16% ethanol by volume, respectively. The latter is considered to be the maximum ethanol content at which yeast can survive, although under certain laboratory conditions, some strains have been found capable of resisting up to 18% vol. Some types of wine may, of course, have even higher alcohol contents, but this results from the addition of ethanol.
Many consumers place excessive importance on alcohol content as an essential quality