Inert substances (inert = inactive, uninvolved) are inert substances that do not participate in certain chemical processes because they do not contain oxygen. These are almost all gases (noble gases), except for the very reactive oxygen. In viticulture, for example, these are nitrogen and carbon dioxide, which are often used as protective gases against undesired oxidation in wine containers. This prevents, for example, the wine from going mouldy (wine defect). So-called inert gas mixtures are produced by burning combustion gases and then contain no oxygen but nitrogen and carbon dioxide. These mixtures are cheaper than, for example, pure nitrogen, which is, however, preferred.
There are bottling plants that fill the empty space (head space) with inert gas before the bottle is capped in order to exclude oxidation. This is particularly important when using screw caps, because the amount of oxygen in the empty space is much greater here. With the so-called internally sealing closures, such as the cork (whether natural or plastic), sealing under vacuum has also been used for a long time, because this prevents too high pressure in the headspace due to the insertion of the cork (too high pressure could lead to it being pushed out). However, sealing under vacuum is now also possible with twist-off closures. Snow-dropping is also used in Australia, where dry ice (solid carbon dioxide) is added. When the dry ice comes into contact with the wine, it immediately evaporates, forcing the air out of the bottle neck. This is followed by immediate sealing. See also on this topic under oxidation, oxygen management and closures.
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