The impact of aging wine in high and low oxygen conditions on the fractionation of Cu and Fe in Chardonnay wine

•Copper(I) sulfide is associated with the hydrophobic copper fraction in wine.•Wine with high protein and stored with low oxygen has increased hydrophobic copper.•Wine with low protein has lower proportion of hydrophobic copper after aging.•Wine with high oxygen has increases in the residual fraction of iron and copper.•Oxidative storage increases most oxidative catalytic form of iron and copper.

Solid-phase extraction has previously been used to fractionate copper and iron into hydrophobic, cationic and residual forms. This study showed the change in fractionated copper and iron in Chardonnay wines with 1-year of bottle aging under variable oxygen and protein concentrations. Wines containing protein in low oxygen conditions induced a decrease (20-50%) in total copper and increased the proportion of the hydrophobic copper fraction, associated with copper(I) sulfide. In contrast, protein stabilised wines showed a lower proportion of the hydrophobic copper fraction after 1-year of aging. In oxidative storage conditions, the total iron decreased by 60% when at high concentration, and the concentration of the residual fraction of both copper and iron increased. The results show that oxidative storage increases the most oxidative catalytic form of the metal, whilst changes during reductive storage depend on the extent of protein stabilisation of the wine.