Oxygen: Making wine

During fermentation, the carbon dioxide given off by the nascent wine prevents exposure to oxygen, but, when fermentation ceases, the wine must be protected from access to oxygen if it is to remain wine. Early winemakers learned that, with very few exceptions, wines had to be kept in full containers at all times lest they change into vinegar.

Modern winemakers have equipment which allows most steps in making wine to exclude oxygen. One of the most effective has been the stainless steel tank in which ullage space can be filled with inert gas to exclude oxygen. Wooden vats, casks, and barrels are not sufficiently impervious for this blanketing technique. Some tanks have lids that can be raised or lowered depending on the volume of liquid in the tank. In older wineries, the oxidation of wine was minimized by frequent small additions of sulfur dioxide, which, although it is needed less frequently as an antioxidant in modern winemaking, is still used to inhibit microbial activity. ascorbic acid has also been used to a certain extent as an antioxidant, but it must be employed in conjunction with sulfur dioxide (see erythorbic acid too). refrigeration of wine in storage slows all reactions, including oxidation, but it has the danger that oxygen solubility increases at low temperatures. The aim of protective winemaking is to minimize oxidation, although see white winemaking for alternative approaches.