Bottling process and closure choice influence oxygen levels in wine and wine post-bottling development

摘要

In the framework of several bottling trials replicating typical winery conditions, Riesling wines were bottled with different levels of dissolved and headspace oxygen and were sealed with co-extruded or screw cap closures in order to investigate the impact of oxygen at bottling as well as oxygen´s ingress through the closure on wine development. Using the luminescence technology, dissolved and headspace oxygen, as well as closure´s oxygen transfer rate were monitored during bottle storage and SO2 losses, aroma, color and sensory properties were analyzed throughout the storage period.Headspace and dissolved oxygen decreased constantly in all treatments due to oxygen dissolution and consumption in the wine and became undetectable in the majority of the cases within one and four months. Decline was slower under cylindrical closures due to additional oxygen ingress from the closure into the bottle. Oxygen ingress through the closure demonstrated two phases: a short but rapid exponential curve during the first weeks followed by a linear phase with smaller slope until the end of storage period – the first representing the oxygen out of the pores of the closure itself, the second the ingress of atmospheric oxygen diffusion through the closure into the bottle, known also as oxygen transmission rate.Oxygen present in the headspace of bottled wine was found to be the main cause of SO2 decline during the first months after bottling, where the main SO2 decline occurs. Headspace oxygen accounted for up to 80% of the total SO2 loss during storage. However, it did not influence color evolution as the color of the Riesling wine tested remained unchanged throughout the trial. Nevertheless headspace oxygen accounted for a significant degree of sensory differentiation of the wines in terms of oxidative. 14 months after bottling wines bottled at low headspace oxygen were perceived as significantly less oxidative than wines with high headspace oxygen even under large headspace volume. This positive effect of headspace management lasted even up to 24 months when small headspace volume was realized. Therefore low concentrations of headspace oxygen via CO2 flushing combined with small headspace volume offered the best possibility to protect the wine from oxygen. In some cases high headspace oxygen appeared to favor some aroma compounds such as ethyl decanoate, ethyl octanoate and cis-Linalooxide (related to fruity, grape and flowery aroma respectively) and to eliminate some others such as H2S and DMS (aromas of rotten egg, cabbage and sulfur). Headspace volume had in many cases the opposite effect: large volume favored production of H2S and reduced DMS and esters. However these effects of headspace management on aroma composition were not perceived by the panelist in the sensory analysis since wines did not differ in terms of fruity, flowery or reductive character. Under low headspace oxygen dissolved oxygen at bottling appeared to be the main factor influencing SO2 losses during the first months. The loss of SO2 was not correlated with the evolution of dissolved oxygen throughout storage, but with the total amount of oxygen consumed by the wine. Dissolved oxygen accounted for significant differences across the wines within the same closure: wines bottled with high dissolved oxygen showed significantly higher ratings for oxidative, confirming the influence of dissolved oxygen management on the evolution of wine over time. In all bottling trials closure was the variable defining the further SO2 losses after the initial rapid decline during the first months due to HSO and DO at bottling. SO2 continued to decrease in a slow manner in wines sealed with synthetic closures while it remained almost unchanged under screw cap closures. Therefore both headspace and dissolved oxygen management at bottling as well as closure choice offer the potential to control to a certain extent SO2 losses. Yet, sealing with closures with low oxygen transmission rate such as screw caps did not prevent significant loss of SO2 when the headspace oxygen was high. On the contrary, keeping headspace oxygen low significantly reduced initial SO2 loss, even under closures with higher oxygen transmission rate. Closure choice had also an impact on sensory development of the wines post-bottling: wines with closures with high oxygen transmission rate (synthetic closure type 1) were more oxidative, while those with moderate transmission rate (synthetic closure type 2) were more fruity. Finally those with low transmission rate (screw cap) got higher scores for CO2 perception and lower for oxidative. However, these wines were characterized by increased concentrations of H2S, a compound described as struck flint and rotten egg.