An efficient method for the rapid assessment of free copper in white wine

Copper can influence wine chemistry in several ways. First, we have demonstrated that copper can mediate oxidative reactions in white wine that lead to enhanced colour development. The interaction of copper, in a reductive mode, with hydrogen sulfide and the link to sulfidic off-odour is a second role.If copper’s interaction with hydrogen sulfide occurs in the presence of thiols such as glutathione, polysulfane formation can occur. In a previous article (Clark et al. 2015), we outlined how residual copper remains in wines after copper fining to remove hydrogen sulfide.We also showed that this residual copper was still active in mediating oxidative reactions.This present article focuses on the perhaps more important role that residual copper plays in protecting the copper-fined wine from producing more sulfidic off-odour. That is, we need to be able to measure the fraction of the total copper concentration that is available to bind any sulfide that may be produced during the ageing of a wine in bottle. Two analytical strategies are outlined: electrochemistry and colorimetry.