Term for a chemical reaction in which one atom or molecule emits electrons (oxidized) and another substance absorbs these electrons (reduced). So with the oxidation is always always one reduction connected. Both processes together are partial reactions of a so-called redox reaction, Originally, the oxidation was solely the chemical reaction of a substance with oxygen Understood. Later, the term was extended to include reactions in which hydrogen atoms are removed from a compound (dehydrogenation).
Oxidizing agents are those substances that can easily absorb electrons, such as oxygen. chlorine and fluorine. The oxidizing agents are reduced in the redox reaction itself. And reducing agents are those substances that easily release electrons, such as hydrogen, carbon and base metals like iron. magnesium and sodium, The reducing agents themselves are oxidized in the redox reaction. In the winemaking Oxidation should only take place in the most precisely dosed and controlled form, because uncontrolled occur frequently wine faults on.
It is, so to speak, Emperor Napoleon III. (1808-1873) that the mostly harmful influence of too much oxygen was clarified. He commissioned the chemist Louis in 1863 Pasteur (1822-1895) to investigate why so much wine spoils. The influence of microorganisms was still completely unknown at the time. Pasteur noted that too much air supply prevented the spread of Acetobacter (Acetic acid bacteria) favors and thus wine too vinegar becomes. But he also discovered that low oxygen influx can positively influence development.
The oxidation of wine takes place in three phases. In Phase 1, oxygen from the atmosphere is taken up to a maximum possible concentration of 9 mg / l at a temperature of 20 ° C and can be measured as dissolved gas in the wine. In Phase 2, the dissolved oxygen combines with easily oxidizable wine components. This bound oxygen can no longer be measured. In the same amount of bound oxygen can be taken up again oxygen. In phase 3, the bound oxygen is transferred to substances that are not directly oxidizable. There he leads to sensory and analytically perceptible consequences.
In the case of wine oxidation is usually disturbing or desired only under controlled conditions. In case of uncontrolled application or unwanted oxygen access flavorings attacked and it often comes to negative taste and color changes, which are different Age tones and Brown break, as well as unwanted Sherryton express. The color scale can change from yellow to yellow amber until dark brown. The wine loses freshness and ages faster. Oxygen contact can also change Acetic acid bacteria and And arrived (Yeasts) multiply, which ultimately make the wine even inedible.
Normally, in the winemaking process, oxygen access is prevented or at least severely restricted. This is already experienced in several stages of winemaking by spraying the mash 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, which indeed creates the resulting carbon dioxide can escape, but no oxygen access is possible. Another option is the whitespace of the fermentation tank with inert gas (Inert gas) fill up. With special wines oxygen influence is very well desired, for example with sherry. Malaga or Vin Jaune,
Some producers promote certain white wine varieties like 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 minimum amounts of oxygen to the wine during the bottle aging through the closure is called nanooxigenation (single atoms) or in a slightly higher amount micro-oxygenation designated. Controlled oxidation methods are called oxidative expansion, The prevention or restriction is called reductive expansion designated. See also the topic under oxygen management,
Complete listings of the numerous vinification measures and cellar techniques, as well as the wine-regulated wine, sparkling wine and distillate types are under the keyword winemaking contain. Comprehensive information on wine law is available under the keyword wine law,