Term for a chemical reaction in which an atom or molecule gives off (oxidizes) electrons and another substance takes up (reduces) these electrons. So there is always one with oxidation reduction connected. Both processes together are partial reactions of a so-called redox reaction, Originally, only the chemical reaction of a substance was used as the oxidation oxygen Roger that. The term was later expanded to include reactions in which hydrogen atoms were removed from a compound (dehydration).
Oxidizing agents are substances that can easily take up electrons, such as oxygen. chlorine and fluorine. The oxidizing agents themselves are reduced in the redox reaction. And reducing agents are substances that easily give off electrons, such as hydrogen, carbon and base metals such as iron. magnesium and sodium, The reducing agents are themselves oxidized in the redox reaction. In the winemaking Oxidation should only take place in the most precisely metered and controlled form possible, because uncontrolled often occur wine faults on.
It is Emperor Napoleon III, so to speak. (1808-1873) to thank that the mostly harmful influence of too much oxygen has been clarified. In 1863 he commissioned the chemist Louis Pasteur (1822-1895) to investigate why so much wine spoils. The influence of microorganisms was completely unknown at the time. Pasteur found that too much air intake prevented the spread of Acetobacter (Acetic acid bacteria) favored and thus wine too vinegar becomes. But he also discovered that low levels of oxygen can have a positive impact on development.
The oxidation of wine takes place in three phases. In phase 1, oxygen is taken up from the atmosphere up to a maximum possible concentration of 9 mg / l at a temperature of 20 ° C and can be measured as a gas dissolved in wine. In phase 2, the dissolved oxygen combines with easily oxidizable wine components. This bound oxygen can no longer be measured. Oxygen can be taken up again in the same amount of bound oxygen. In phase 3, the bound oxygen is transferred to substances that cannot be directly oxidized. There he leads sensory and analytically noticeable consequences.
In wine, oxidation is usually disruptive or only desired under controlled conditions. In the event of uncontrolled use or unwanted oxygen access flavorings attacked and there are often negative changes in taste and color, which are different Age tones and Brown break, as well as unwanted Sherryton express. The color scale can range from yellow to amber range up to dark brown. The wine loses freshness and ages faster. Through contact with oxygen can also Acetic acid bacteria and And arrived (Yeasts) that ultimately make the wine inedible.
Access to oxygen is normally prevented or at least severely restricted during winemaking. This is already done at various stages of wine production by spraying the mash with it ascorbic acid and / or by adding sulfur reached. The fermentation usually takes place in the absence of oxygen ( anaerobic Condition). This is achieved by closing the fermentation tank with a Gäraufsatz, whereby the resulting carbon dioxide can escape, but no oxygen access is possible. Another option is that whitespace of the fermentation tank with inert gas (Shielding gas). For special wines, the influence of oxygen is very desirable, for example with sherry. Malaga or Vin Jaune,
Some producers promote certain types of white wine such as Chardonnay a certain oxidation of the must before fermentation because it releases certain flavors. The metered supply of oxygen or air to the must or wine in various stages of winemaking is called ventilate (Aeration). The supply of the smallest amounts of oxygen to the wine during the bottle aging due to the closure is called nanooxygenation (single atoms) or in a somewhat higher amount micro-oxygenation designated. Controlled oxidation methods are called oxidative expansion, The prevention or limitation is called reductive expansion designated. See also on the topic below oxygen management,
Complete lists of the numerous vinification measures or cellar techniques, as well as the wine, sparkling wine and distillate types regulated by wine law are under the keyword winemaking contain. There is extensive wine law information under the keyword wine law,