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40 WINES&VINES May 2016 WINEMAKING PRACTICAL WINERY & VINEYARD Your success is our prioritY In fluid mechanics, it has been proved by Osborne Reynolds that turbulence depends on the mean flow velocity, pipe diameter, density and fluid viscosity. 14 A turbulent flow greatly increases the surface area of reaction with ambient air, thereby increasing oxygen dissolution. With a higher transfer flow ve- locity and frequent pumping, dissolution of oxygen is usually more important, especially if a centrifugal pump is used. Analysis of audits 4, 7 and 11 reveals good practices able to reduce DO during critical moments of one transfer, which re- duces the U-curve effect. Whenever a wine is moved from one container to another, it should be protected with inert gas. The process of sparging with inert gas is based on the application of Henry's law, 13 which states that the solubility of a gas in a liquid is proportional to the partial pressure of that gas in the gaseous atmosphere in contact with the liquid. During sparging, a partial pres- sure develops between the inert gas (N 2 ) and the dissolved gas (O 2 ). The difference in partial pressure causes O 2 to leave the wine. According to Henry's law, many factors would affect the efficiency of sparging. These factors include temperature of the wine, inert gas bubble size, gas pressure, contact time between the gas and wine and the flow rate of gas in relation to the flow rate of wine. Small, inert gas bubbles create a greater interface area with the wine, leading to a more efficient stripping of oxygen. The bubble size is determined by the porosity of the sintered element in the sparging unit. Iowa State University's extension enologist Murli Dharmadhikari noted that a maximum bubble size of about 0.03 mm diameter is considered acceptable for sparging. 15 Dharmadhikari noted that to displace oxygen, the tanks should be purged with 3 to 7 volumes of CO 2 . He also suggested a temperature of 59° to 68° F, a pressure of 1 to 2 bars and a flow rate of 0.1 to 0.3 liters of inert gas per liter of wine to improve The importance of managing headspace level for screwcaps has been emphasized in scientific literature. If not appropriately purged with nitrogen, the closure will compress a higher level of oxygen under the cap. CLOSURE EFFECT ON HEADSPACE OXYGEN AT BOTTLING 3 2.5 2 1.5 1 0.5 0 HSO mg/L A8 A1 A3 A5 A9 A10 A11 A16 A18 A6 A7 A12 A13 A15 A2 A4 A14 A17 Audit Number Agglomerated cork Natural cork Nomacorc Screwcap