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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 65 W I N E M A K I N G driven by the closure OTR. Figure 3 shows SO 2 data from the cur- rent red wine closure trial. Wine under screwcaps typically lose less SO 2 over time due to the inherently lower OTR, with wine under other closures showing vari- able performance, depending on closure type and supplier. It should be remembered that SO 2 does not interact directly with oxygen but rather with a range of oxidized wine components at the end of a chain of chemical reactions. As such, it is not surprising that the graph after the six-month time period does not present a smooth curve, as the SO 2 concen- tration is dependent not only on the avail- able oxygen but also on depletion of other wine components in the oxidation process. This interdependence of SO 2 , oxygen and other wine components can be seen in the relationship with DMS. Figures 4 and 5 show the strong rela- tionship between DMS concentration and the loss of free SO 2 through each closure between six and 36 months for the cur- rent red wine and most recent white wine closure trials. The loss of free SO 2 between bottling and six months storage is predominantly due to the TPO at bottling rather than the Screw caps Alterna ves Natural Cork Technical Cork 30 25 20 15 10 5 0 0 6 12 18 Months 24 30 DMS concentra on (µg/L) Figure 2: DMS concentration changes in red wine under different closure types over 36 months. Error bars indicate minimum and maximum values for each closure type (highlighted area shows DMS detection threshold of 20 to 25 μg/L). Screwcaps Alterna ves Natural Cork Technical Cork 35 30 25 20 15 10 5 0 0 6 12 18 Months 24 30 36 Free SO 2 (mg/L) Figure 3: Free SO 2 decline in red wine under different closures during 36 months of storage. Error bars indicate minimum and maximum values for each closure type. Dotted line represents nominal end of shelf life (10 mg/L free SO 2 ). LOTUS: Breakthrough Pump Over Technology Lotus gently and uniformly distributes juice over the cap in tanks of any size without excessive bruising or misting. Lotus is compact, continuously adjustable, has few moving parts and is easy to install and clean. Three sizes available. Prices start at $650 The next generation of pump over technology is here. Napa Fermentation Supplies 575 Third St. Bldng. A Napa CA 94559 napafermentation@aol.com | 707-255-6372 www.napafermentation.com