inert gas mixture, mixture of gases that does not include oxygen. Traditionally, such mixtures have been composed of nitrogen and carbon dioxide but more recently argon is being included in these mixes, either in place of, or along with, nitrogen. Such mixtures are used in wine storage processes in lieu of nitrogen because the greater density of carbon dioxide and argon causes them to layer and so more efficiently exclude oxygen. Inert gas mixtures may not have been used in winemaking as often as nitrogen because the carbon dioxide fraction dissolves in wine, possibly leaving a higher-than-desirable residual concentration of this gas. Argon, like nitrogen, has a very low solubility in wine and inert gas mixtures of either or both of these two with carbon dioxide can, with modern metering equipment, be selected to leave a residual level of dissolved carbon dioxide that is optimal for the style of wine under storage. Inert gases are also used to flush the oxygen from hoses and pumps, and during bottling.