South Africa Wine Technical Yearbook 2025

A recent study investigated the OTR of different bottle closures after 12 years of bottle storage (OTR T12 ) of a Sauvignon blanc wine. This study aimed to examine: 1. The long-term OTR of various wine bottle closures. 2. How different closure types affected the chemical and sensory composition of a Sauvignon blanc wine. 3. The relationship or correlation between closure OTR T12 levels and the preservation or degradation of key aroma compounds during bottle storage. The main findings are summarised in this article. Materials and methods Sauvignon blanc wines were obtained from three French appellations. The wines were bottled, sealed with different closure types, and stored for 12 years. The following closures were tested: • 28 x Natural corks. • 38 x Microagglomerated corks (Types A, B and C). • 11 x Synthetic stoppers. • 5 x Screw caps with Saran-Tin liner. • 6 x Screw caps with Saranex liner. The following parameters were analysed after 12 years of storage: • OTR T12 . • Volatile thiols (3-mercaptohexan-1-ol (3MH), 4-mercapto-4-methylpentan-2-one (4MMP) and 2-furanmethanethiol (FFT)). • Oxidation markers (methional and phenylacetaldehyde). • Dissolved carbon dioxide. • Sulphur dioxide. • Sensory analysis. Results: OTR The OTR of the various closures after 12 years differed significantly. • Lowest OTR T12 measured: One of the Saran-Tin-lined screw caps (~ 0.05 mg/year). • Lowest average OTR T12 : Saran-Tin-lined screw caps (~ 0.1 mg/year). • Lowest variability (good consistency and repeatability): Saran-Tin-lined screw caps (OTR T12 range ~ 0.05 - 0.14 mg/year). • Highest OTR T12 measured: One of the natural corks (~ 89.1 mg/year). • The highest variability was in natural corks (OTR T12 range ~ 0.1 - 89.1 mg/year). Although some corks allowed a high oxygen ingress, some performed exceptionally well and can be compared to the Saran-Tin-lined screw caps. Higher variability can be expected for natural cork closures due to the individual structural variability between the stoppers. • The Saranex-lined screw caps had a surprisingly high average OTR T12

(~ 9.58 mg/year) and high variability (OTR T12 range ~ 0.1 - 31.5 mg/year). This could be due to mechanical damage on the surface of some of the screw caps during ageing. • The synthetic stoppers had a moderate average OTR T12 (~ 0.86 mg/year) with relatively low variability (OTR T12 range ~ 0.4 - 1.7 mg/year). • The microagglomerated corks had variable average OTR T12 , with type A having a low average OTR T12 (~ 0.5 mg/year) with low variability, while the other two types (types B and C) showed higher average OTR T12 values (~ 4.1 and 6.2 mg/year, respectively) with increased variability. • The closures that showed the most similar OTRs after 12 years of storage (when compared to the OTR reported by the manufacturer at the time of bottling (OTR T0 )) were the Saran-Tin-lined screw caps and one type of microagglomerated cork. • Other closure types showed increased OTR T12 , probably due to reduced mechanical performance and increased OTR. These changes can be due to structural changes over time, such as drying and elasticity loss, resulting in increased OTRs. Results: Effect on wine composition Three distinct groupings can be made based on the chemical analyses of the wines after 12 years of ageing: Group 1: Average OTR T12 ~ 0.3 mg/year (range ~ 0.2 - 0.9 mg/year) • Screwcap Saran-Tin. • Microagglomerated cork type A. • 2 x Natural corks. These wines had the lowest oxidative evolution, the highest concentration of volatile thiols and FFT, and the lowest concentration of oxidation-related compounds. Group 1 and Group 2 had similar dissolved carbon dioxide concentrations. Group 2: Average OTR T12 ~ 0.8 mg/year (range 0.2 - 2.7 mg/year) • Synthetic stoppers. • Microagglomerated cork types B and C. • Screwcap Saranex. • 5 x Natural corks. These wines showed early signs of oxidation, with decreasing concentrations of volatile thiols and emerging oxidation-related compounds. Group 3: Average OTR T12 ~ 14.7 mg/year (range 2.1 - 60 mg/year) • Microagglomerate cork C. • 9 x Natural corks.

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TECHNICAL YEARBOOK 2025