Sulfur Dioxide-Oxygen Consumption Ratio Reveals Differences in Bottled Wine Oxidation

The availability of oxygen to a wine after bottling can have both beneficial and detrimental effects over time, which may be altered by the wine's storage history. A Chardonnay wine underwent four different aging treatments: aged in stainless steel with and without lees and aged in oak barrels with and without lees. After six mos of aging, the wines were bottled and subjected to four levels of oxygen exposure by differences in bottle closure. The wines were then monitored for dissolved, headspace, and total consumed oxygen (TCO) concentrations, SO2, aldehydes, esters, and many other standard endpoints. After bottling with substantial oxygen uptake, oxygen consumption was slow, with 0.5 mg/L dissolved oxygen persisting in some bottles after six mos. SO2 concentration decreased and absorbance at 420 nm increased in response to higher accumulated oxygen exposure, expressed as TCO. A comparison of oxygen versus SO2 consumed by the wine provided new insights into the development of oxidation products. Wines aged on yeast lees consumed more SO2 for each equivalent of oxygen consumed. As these wines also had lower levels of weak SO2-binding agents, we hypothesized that these agents interfered in SO2-mediated protection against wine oxidation. At 12 mos after bottling and using descriptive analysis, the 16 wines were rated for 13 attributes determined by 14 judges in triplicate. The aging container, consisting of either stainless steel or oak barrels, had the largest impact on the descriptive analysis followed by oxygen availability through the bottle closure. Wines with the highest TCO had noticeably oxidized characters. The ratio of SO2 versus O-2 consumed may help identify wines that will become oxidized. SO2-binding agents and their role in affecting wine oxidation and SO2 analysis needs clarification.