Inhibiting Malo-Lactic Fermentation in Australian Dry Red Wines by Adding Fumaric Acid

Abstract

Added fumaric acid delayed bacterial malo-lactic fermentation in three young Australian commercial dry red wines from <i>Vitis vinifera</i> L., `Shiraz9 variety, grown in different wine areas in South Australia (Berri, hot region; Adelaide, warm region; and Coonawarra, cool region). The delay increased with the concentration of fumaric acid (up to 1.5 g/l), and the increase was synergistic (multiplicatively) with decreasing pH (4.1 to 3.5). The wines themselves varied somewhat in the effect of fumaric acid. The acid proved bactericidal to added wine leuconostocs, drastically reducing the numbers of viable bacteria in two days. In many cases the wines with fumaric acid addition had not undergone malo-lactic fermentation by 41 weeks even though conditions were ideal for bacterial growth: storage at 25°C, no added sulfur dioxide, and no removal of yeast sediment. When malo-lactic fermentation occurred, both fumaric acid and L-malic acid were degraded. The acids were converted stoichiometrically to L-lactic acid — one mole of substrate resulting in one mole L-lactic acid. The probable pathway of fumaric acid degradation by the wine leuconostocs in the fermentation is by conversion to L-malic acid catalyzed by fumarase, with subsequent malo-lactic fermentation yielding L-lactic acid and carbon dioxide.