Chemical element (O) whose Latin name Oxygenium is derived from the Greek "oxys" for "pointed, acidic". Actually, the name is wrong, because oxygen was previously held responsible for the formation of acids. That hydrogen is the cause of the acid character was only recognized later. At 21%, the colourless, odourless and tasteless gas forms the atmosphere together with nitrogen (78%) and carbon dioxide (0.04%). It is the main component in water and also contained in numerous compounds of the earth's crust. At around 50%, it is the most abundant element on earth. It is released during plant photosynthesis, in which sunlight, water and carbon dioxide are involved. Almost all animals and most plants need oxygen to live. In high concentrations, however, it is toxic to most living things. Oxygen is extremely reactive and combines very quickly with most substances.
During vinification it plays a decisive role either through aerobic (presence) or anaerobic (absence) action. Oxygen can have both positive (see under aeration) and negative (see under oxidation) effects on must and wine. At the beginning of fermentation, oxygen causes the yeasts to multiply. For this, the smallest amounts of oxygen are sufficient, which are dissolved from the must. Larger quantities are usually harmful. In various stages of winemaking, sulphur compounds and other substances are mainly used as oxidation inhibitors and preservatives. The carbon dioxide produced during fermentation protects against oxygen, but in the end oxidation must be prevented, otherwise vinegar or a spoiled, oxidised wine will inevitably be produced. This is best achieved by closed fermentation tanks made of stainless steel, whose empty space is filled with inert gas (protective gas) if necessary. As an alternative to this, a low and controlled contact with oxygen is deliberately permitted during reductive ageing.