Enzyme aroma improvement is grape specific
wine can benefit from enzyme-treatment to enhance aroma, reports
Kim Hunter Gordon.
The aroma and flavour of wine is partly influenced by non-volatile compounds held together by bonds, which are broken down by enzymes called glucosidases. These enzymes are naturally occurring in grapes and yeast but are largely inactive at the pH levels of winemaking and are highly variable between and within harvests.
Glucosidases taken from certain species of fungus, however, are effective at wine pH and can be added to a finished wine. Doing so should, in theory, guarantee the full aroma of the variety, at least in white wine. In red wine, the enzyme can destabilise the wine's colour.
But a study to be published in the Journal of the Science of Food and Agriculture next month (85:199-205) found that the process does not work in wines made from all grape varieties. For example, the enzymes enhanced the aroma in the Maria Gomes grape but offered no improvement at all in the Bical variety.
The study compared treated wines to untreated ones. It employed a panel of wine tasters to complement a gas chromatography-mass spectrometry analysis giving the proportions of flavour-producing components.
The improvement in flavour of the Maria Gomes grape variety was attributed to a 32 per cent increase in terpenoids (compounds common in Muscat and Riesling varieties), a 32 per cent increase in esters (sweet smelling compounds) and a 19 per cent increase in aromatic alcohols (despite a 10 per cent drop in the overall alcohol level).
The Bical variety contained very few terpenoids to begin with in comparison, saw the same increase of aromatic alcohols (but an increase overall) and a lesser rise in esters.
The authors conclude that this technique of improving wine is dependent on the aromatic potential of the grape variety. The announcement will be of interest to winemakers who may be investing in an enzymatic treatment that could be providing little or no benefit to the wrong grape.