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May 2016 WINES&VINES 41 PRACTICAL WINERY & VINEYARD WINEMAKING sparging efficiency. And for removing the oxygen already dissolved in the wine, he also recommended sparging the hose with gas and the wine during pumping. 15 Best practices for reducing DO and U- curve effect during bottling are summarized in the table "Best Practices for Managing TPO at Bottling" (page 44). Reducing oxygen uptake during and after filling At the filling step, oxygen dissolving into wine is due to variation in bottle headspace related to improper fill height, wine temperature, solubility of gases, bottle size and shape. Failing filler spouts drive air into the bottle, resulting in an improper application of inert gas. The key components regarding filling and how it affects oxygen uptake re- late primarily to the turbulence of flow from the filling spouts and the use of vacuum or inert gas during filling. A rapid, non-turbulent flow will decrease the uptake of oxygen and should be the first priority, even if a vacuum is used to evacuate air from the bottles or inert gas is sparged into the bottles. As observed in audits 1 and 10, even with the use of vacuum and inert gas after filling, the final TPO level in both cases was higher than 1.5 mg/L. There are many other factors probably not controlled for. When flowing from the spout into the bottle, the wine encounters both stainless steel and rubber surfaces. These should be maintained to be as smooth as possible with regular inspection and, when necessary, re- machining of the filling spouts surface to ensure a desirable laminar flow with proper maintenance of the filler spouts. Use of inert gas Inert gas is used to evacuate air from the bottle and/or the headspace above the wine. Nitrogen and carbon dioxide are the gases of choice, as argon has a tendency to increase pressure in the bottle when the wine tem- perature increases. Compared to nitrogen, CO 2 has the advantage of being soluble in wine, which minimizes the pressure pro- duced by the reduction of headspace volume until saturation. This does, however, have the disadvantage of increasing the dissolved CO 2 content in the wine. While its presence as a "spritz" may be acceptable in some white wine styles, it is less desirable in red wines. Moreover, CO 2 dissolution can reduce potential oxygen levels immediately and can increase the likelihood of the wine becoming reductive. Consequently, it is recommended that winemakers set low CO 2 levels, espe- cially for red and full-bodied white wines. The Australian Wine Research Institute sug- gests 1 to 1.2 mg/L of CO 2 under cork and 0.6 to 0.7 mg/L under screwcap. 16 An empty bottle contains approximately 225 mg of oxygen, which can increase DO in the wine by 0.3 to 0.7 mg/L, depending on the filling technology adopted (carousel or orbital). One way to remove oxygen from the bottle is to purge inert gas prior to filling, although in some cases it appears inefficient, as seen in table "Managing Oxygen During and After Filling" (page 38). Winemakers recommend a volume of gas seven to eight times that of the bottle, depending on the turbulence and rate of purging. Nitrogen and carbon dioxide are the gases of choice, as argon has a tendency to increase pressure in the bottle when the wine temperature increases.