Influence of temperature, copper and CO2 on spore counts and geosmin production by Penicillium expansum

Abstract

Background and Aim: Musts and wines produced from rotten grapes often have an earthy/musty odour, with geosmin the responsible compound. Penicillium expansum is considered a potential source of geosmin in rotten grapes from vineyards treated with copper-based fungicides. Methods and Results: The laboratory study assessed the influence of temperature (10-30°C), copper concentration (0-76.50mg/L) and CO2 in the headspace (0.03-3%) on the spore count and the production of geosmin by P.expansum according to a Doehlert design. The spore count and the production of geosmin (ng/mg biomass) were significantly correlated (r=0.78). Copper had no significant effect on the spore count but was the most important factor for explaining geosmin production. The production of geosmin was enhanced at low temperature (15°C), 0.03% CO2 (i.e. atmospheric level) and high copper concentration (76.50mg/L). Conclusion: Penicilliumexpansum, grown on Czapek agar, produced a significant amount of geosmin at low temperature and in the presence of copper. Significance of the Study: This study suggests a possible explanation for the occurrence of earthy/musty odours in musts and wines made from rotten grapes. © 2012 Australian Society of Viticulture and Oenology Inc.