The effect of wine cork closures on volatile sulfur compounds during accelerated post-bottle ageing in Shiraz wines

Abstract

Reduced off-flavour is an organoleptic defect due to an excess of volatile sulfur compounds (VSC) in wine and often happening in Shiraz wines. This off-flavour is a direct consequence of the lack of oxygen flow during winemaking and bottle storage. Therefore, wine closure could have a direct impact on the formation of VSC due to the oxygen transfer rate that can modulate their levels. Even if dimethylsulfide (DMS) contributes to reduced off-flavor, it is also a fruity note enhancer in wine and its evolution during wine ageing is not well understood. Until now, we knew that DMS was mainly released from S-methylmethionine and DMSO during wine ageing. Chemical equilibrium between DMS and all the DMS precursors called also DMS potential (DMSP) are not well understood and the influence of the closure permeability has never been investigated. In this study, we studied (a) the evolution of 7 VSC in Shiraz wines by GC-MS/MS according to several closure permeabilities and (b) the equilibrium between DMS-DMSP during accelerated wine ageing. In practice, 6 Shiraz wines were collected from 2 regions in France and bottled under anaeroby conditions with 4 different wine closures made with micro-agglomerated cork exhibiting 4 different oxygen transfer rates. VSC and DMSP were analyzed by HS-SPME-GC-MS/MS at the beginning and after 3 months of storage at 35°C. Globally, the total amount of VSC increased after 3 months of accelerated ageing, corroborating that reduced off-flavour can appear during bottle ageing due to hypothetic decomplexation mechanisms. Among the 7 analyzed VSC, only 3 (H2S, MeSH and DMS) showed significant changes in their levels during wine ageing. Indeed, the levels of H2S increased by a factor of 1.4 ± 0.5. The type of closure seemed to modulate the production of H2S, but no evident relation has been found. For MeSH, an overall increase was observed and was equal in average to a factor of 5.2 ± 2.7. For DMS, a significant increase of a factor of 5.1 ± 2.5 was observed and a general tendancy appeared : the most permeable closures induced a smaller production of DMS during ageing. It appeared that DMS could escape through the closure and that the loss was proportional to the permeability of the closure. Since DMS came from the chemical degradation of DMSP, we studied the evolution of DMSP during wine ageing. As expected, DMSP levels decreased during ageing by a factor of 1.5 ± 0.4 and we observed a correlation with closure permeability : the most permeable closures favoured the degradation of DMSP, suggesting that oxygen level could play a role in this mechanism. Under accelerated ageing conditions, VSC levels increased significantly and could reinforce the reduced off-flavour of Shiraz wines. For the first time, closure permeability and so, indirectly oxygen level, could play a role in the DMSP degradation. From a technical point of view, closures with a very low permeability seem to be recommended to preserve DMS.