OTR determination of aged closures: Impact on aroma compounds composition of Sauvignon blanc wines

Abstract

Oxygen transfer rate (OTR) is a technical property of closure, and it modulates the oxygen supply to the wine during its bottle aging. It’s an important parameter to take into account in the analysis of wine aroma evolution. OTR distribution is well documented for new closures, but little research has been published on its determination for aged closures. Initial oxygen release after bottling impacts the composition of wines during the first years of storage), but the link between OTR, sensory perception and aroma composition after many years of aging has not yet been clearly studied. 

This study aimed at assaying the OTR of closures by coulometry as well as the determination of eight revelant volatile molecular markers by GC-MS/MS, including 3-SH, 3-sulfanylhexanol acetate (3-SHA), 4-MSP, Ethyl-2-sulfanylacetate (E2SA), furfurylthiol, methional, phenylacetaldehyde and sotolon. Additional enological parameters were also studied such as dissolved CO2, free and bound SO2, and OD420. Oxidation intensity was also evaluated by a trained panel. The goal was to evaluate the correlation between OTR value of aged closures, concentration of chemical markers and sensory analysis of wine samples. 

We applied this methodology to two set of wines. In a first experiment, a Sauvignon blanc wine sealed with eight different types of closures (natural corks, three microagglomerate corks, two synthetics and two screw caps), was analysed after fourteen years of aging. Our results reveal that, comparing to other stoppers, natural corks exhibit the greatest variability with OTRs values ranging from 0.38 mg/year to 44.9 mg/year. This oxygen transfer rate significantly impacts the balance between thiols vs. other oxidation related compounds.

In a second part, nineteen whites wines from different wineries from a same appellation, sealed with different stoppers (natural and microagglomerate corks) were selected. We demonstrate that regardless of the intrinsic quality of the wine, after six years of aging, OTR plays a fundamental role in the shelf life of the wine. Based on our results, OTRs < 0.3 mg/year seem to delay the premature oxidation characteristics (loss of varietal thiols and increase in oxidation markers). These observations were confirmed by sensory evaluation of wines.