flavour precursors, include glycosides, or sugar derivatives, of compounds that would otherwise be flavour-active. These flavourless compounds occur naturally in grapes (and many other fruits) as products of the normal metabolic activity of the fruit, and they are both numerous and more abundant than the free flavour compounds. Their importance to wine comes from their ability to release and so augment the level of flavour compounds, some positive, some less so. In the case of glycosides, this release is by hydrolysis. This may be a prolonged process during ageing, for example, or one accelerated through the use of enzymes in the winemaking process. Both chemical and sensory studies at the australian wine research institute have demonstrated that flavour precursors are important in development of varietal flavours and bouquet in wines. Because many flavour precursors are glycosides, quantification of this class of compound through measures of glycosyl-glucose in grapes has been suggested as an indicator of grape quality although research is underway to find quicker analytical techniques.
