The colorimetric measurement of free and bound Cu in white wine

Copper (Cu) is often added to wine to treat or prevent the accumulation of hydrogen sulfide and its assocaited odour. However, Cu in wine can affect oxidative and reductive ageing mechanisms and the rate at which they occcur. Recently it has been shown that the Cu in wine exists predominantly in tow forms whereby it is either bound to sulfide (bound) or not bound to sulfide (free). the measurement of free Cu can potentially provide a means of better understanding the activity of Cu in wine and how it affects reductive and oxidative aspects of wine. However, the current measures of Cu forms are labour-intensive and require expensive equipment not generally found in wineries. This paper describes the development of a routine colorimetric method to allow the determination of free Cu in white wine, which, combined with total Cu concentrations, also allows calculation of the bound Cu concentration. Further work is till required to understand exactly how and if the free Cu concentration of wine at bottling can be optimised to avoid the accumulation of 'reductive' aromas in wine.