Some of the by-products of alcoholic fermentation are listed in Table 2.2.1, above. Glycerol provides sweetness and viscosity to the wine, affecting mouthfeel (body), but not aroma. The normal content in wine is 3–14 g/l but there is a higher concentration in ‘noble rot’ wines, as the fungus Botrytis cinerea produces glycerol in significant quantities. Specific yeast strains and high temperatures will also cause higher glycerol levels (Romano et al., 1997).