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64 p r a c t i c a l w i n e r y & v i n e ya r d J U n e 2 0 1 4 Changes in red wine color and mouthfeel during bottle aging are influenced by pH and choice of bottle closure. Bottling wines at lower pH and with slight oxygen exposure through the closure can lead to more stable color for the next 24 months and potentially lower astringency. R ed wine astringency is influenced by many factors including tannin concentration, tannin composition and wine matrix components such as ethanol, pH, oxygen and metal ions. Research at the Australian Wine Research Institute recently has increased its focus regarding the role of these wine matrix components in tannin for- mation and wine astringency. Under- standing their influence during wine aging could provide winemakers with options to control mouthfeel in fin- ished red wines. A study investigated the influence of pH and screwcap closure type on wine color and tannins during bottle aging. 1 A single- vintage Cabernet Sauvignon wine was produced using standard winemaking techniques. Just prior to bottling, the wine pH was adjusted to either pH 3.2, 3.5, or 3.8 and it was bottled under screwcap using either a SaranTin (ST) liner (to restrict all oxygen ingress) or a Saranex (Sx) liner (to allow minimal oxygen ingress). Changes in color and tannin were monitored for/during the next 24 months. How tannins change with aging Changes in tannin concentration and structure have not previously been mea- sured as part of an aging trial, but trends have been previously investigated using a vertical series of wines. 2 The difficulty in drawing conclusions from a vertical series is that the inevitable growing year differences in grape composition and potential differences in winemaking style can alter the initial wine composition. The objective for this project was to monitor changes in a single-vintage wine over time in bottle. During the 24 months in bottle, a sub- stantial decrease in tannin concentration was observed (Figure 1a), presumably due to the degradation of tannins into smaller molecules since the tannin molecular size w i n e M a K i n g Jacqui McRae and Paul Smith, The Australian Wine Research Institute, Adelaide, SA, Australia BY Closure selection and pH influence on red wine color and tannin during bottle aging ready to drink: Decisions about wine ph and oxygen exposure in bottle can give winemakers some control over tannin and color development during aging. Photo by eric Wilkes AT A GLANCE • A study has been set up to investi- gate the influences of pH and screw- cap closure type on wine color and tannins during bottle aging. • Changes in tannin concentration and structure have not previously been measured as part of an aging trial, but trends have been previously investigated using vertical series of wines. • A decrease in tannin concentra- tion has long been speculated as the reason for the change in wine texture with aging, however this is the first study to confirm that this does occur. Figure 1. general trends in tannin concentration (a) proportion of pigmented tannin (as a percent of the total tannin), (b) wine color density, (c) hue and (d) in Cabernet sauvignon wine with bottle aging. results shown are averages of all wines under both closures and all ph levels to show over- all trends.