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p r a c t i c a l w i n e r y & v i n e ya r d d e c e M B e r 2 0 1 4 67 W I N E M A K I N G crease dramatically beyond this limit dur- ing the last 12 months of the white wine trial, suggesting that another transition in the wine chemistry has occurred. H 2 S changes may be related to sulfide precursor production and chemical path- ways becoming more active once all of the oxygen introduced at bottling has been consumed. The exact nature of the rela- tionship between H 2 S and oxygen is not as clear as it appears with DMS. The closures showing the smallest in- creases in H 2 S during the latter period of both the red and white wine trials have the highest OTRs, suggesting that the ad- ditional oxygen permeating through the closure may be involved in chemical reac- tions that suppress production of H 2 S. This is consistent with the trend seen with the DMS data. A different trend is apparent for MeSH in the white wine trial (Figure 9), where higher levels are observed with wine under higher OTR closures. MeSH levels seen in the white wine trial are, on av- erage, six times higher than the sensory threshold of 1.5 µg/L and therefore likely to play a role in the aroma profile of the wine. Sensorially, it is surprisingly difficult Screw caps Alterna ves Natural Cork Technical Cork 3.0 2.5 2.0 1.5 1.0 0.5 0 0 6 12 18 Months 24 30 H 2 S concentra on (µg/L) Figure 6: H 2 S concentration changes in red wine under different closure types over 36 months. Error bars indicate minimum and maximum values for each closure type (detection threshold of 1 μg/L shown by dotted line). 1.5 1.2 0.9 0.6 0.3 0.0 0 6 12 18 Months 24 30 36 MeSH concentra on (µg/L) Screw caps Alterna ves Natural Cork Technical Cork Figure 7: MeSH concentration changes in red wine under different closure types over 36 months. Error bars indicate minimum and maximum values for each closure type (detection threshold of 1.5 μg/L shown by dotted line). beauty and brawn Stockton, CA 95205 • 209.944.0921 westernSquare.com Lean, Green and Made in America WESTERN SQUARE I N D U S T R I E S