A colourless, odourless, viscous, sweet-tasting liquid that is a byproduct of fermentation. In red wines there are about 4–10 g/L and noble rot wines contain 20+ g/L. Glycerol has been considered to add a positive, rich, oily mouthfeel to wine, however, studies have shown that other traits, like alcohol level and residual sugar, have a greater effect on mouthfeel.