Shiraz ferments were injected with different levels of oxygen (20% and 40% O2 as gas mixtures) to assess the impact of early oxygen exposure on wine tannins and colour measures after fermentation, and after 2 and 12 months bottle-ageing under either Saranex™ or Saran Tin™ screw caps. The O2-treated ferments contained lower concentrations of anthocyanins and tannins, and tannin composition showed lower molecular masses, conversion yields, and proportions of prodelphinidin subunits than those from the control ferments. The colour measures and tannin characteristics of the control wines after 12 months resembled those of the O2-treated wines at 2 months bottle-ageing, and oxygen exposure during fermentation had a greater impact on tannin structure than closure type. Early oxygen exposure during winemaking may result in wines with phenolic compositions that are characteristic of more aged wines, which may reduce the need for extended wine ageing. Display omitted