Incombustible, colourless and odourless, acid gas (also carbon dioxide) with the molecular formula CO2. Colloquially, carbon dioxide is very often incorrectly referred to as carbonic acid. In solid form as dry ice, it is used as a coolant. The gas is produced during all combustion processes and also during the respiration of animal and human beings. It also occurs in volcanic rocks and at great depths.
In the atmosphere, carbon dioxide makes up only a tiny fraction of 0.039%, but this tiny amount is indispensable for all life, because it is needed by plants during photosynthesis and oxygen is formed in the process. Since industrialisation, the proportion has increased by around 44% in connection with climate change and the associated greenhouse effect. The proportion is greater in the northern hemisphere (due to the larger land mass). The resulting extreme weather conditions with heat waves also have a negative impact on viticulture (see under decarbonisation).
Carbon dioxide dissolves in liquids as well as in wine depending on pressure and temperature. When it dissolves, carbonic acid is also formed by reaction with water in the smallest amount of only 0.2%. By far the largest part, however, with over 99%, is the carbon dioxide dissolved in the wine (which does not yet produce carbonic acid), which is combined with the actual carbonic acid as "free carbonic acid". As the vine grows, the sugar in the grapes is formed from carbon dioxide and water. During fermentation, the sugar is then converted into carbon dioxide and alcohol.
At 1.98 g/l, carbon dioxide is about 1.5 times heavier than air. Therefore, there is a danger of suffocation in the fermentation cellar if the gas is not removed by means of exhausters. The formation of carbon dioxide is promoted by yeast sediment storage, as well as by ageing in stainless steel tanks. In wine or sparkling wine, 1 bar corresponds to about 3 g/l, at 2 bar 4.4 g/l and at 3.5 bar about 6.5 g/l (measured at 20 °C). Still wines may contain a maximum of 3 g/l. Sparkling wine must have at least 3.5 bar overpressure. The recommended or prescribed quantities are (measured at 20 °C):
Wine type |
recommended/prescribed |
Carbon dioxide in g/l |
White wine | recommended | 1,2 to 1,5 |
Rosé wine | recommended | 1.0 to 1.5 |
fresh red wine | recommended | 0.5 to 0.7 |
strong red wine | recommended | < 0,6 |
semi-sparkling wine | recommended | 3 (1 bar) to 5.1 (2.5 bar) |
Sparkling wine (see also under sparkling wine) | prescribed | 6.5 (3.5 bar) to 9.8 (6 bar) |
Although carbon dioxide does not belong to the acids, it intensifies a sour sensation and has a great influence on the sensory characteristics. In white wine and rosé wine it has a refreshing and lively effect. If the concentration is too low, especially in white wine, it can create a hollow (empty) taste impression. In red wine, on the other hand, it is usually perceived as disturbing because it increases the astringent effect of the tannins, thus creating a sharp taste impression and masking (covering) aromas. In red wines intended for quick consumption, such as Beaujolais Nouveau, a higher proportion is produced by the method of vinification and is also desired there. In the case of sparkling wine, a minimum quantity is stipulated by wine law, whereby particularly fine bubbles or high sparkling properties are important quality criteria.
Refreshing is advisable for white wine below 0.7 g/l and for red wine below 0.4 g/l. To achieve the desired level of carbon dioxide in the wine, it must be measured regularly and regulated if necessary. An increase or reduction is achieved by means of a gassing fitting. There are various methods for measuring the pressure. Titration is recommended by the OIV, which requires appropriate laboratory equipment. The simplest method for still wine is the Veitshöchheim shaking cylinder, which consists of a riser tube, thermometer and conversion table. In the closed measuring cylinder, the carbon dioxide is "shaken out" of 100 ml of wine and, depending on the content, a corresponding amount of wine is displaced from the cylinder. For sparkling wine, the pressure in the bottle can be determined with an aphrometer.
There are also other uses of carbon dioxide in winemaking. In the impregnation process, it is used to create semi-sparkling wine. When maceration is used in red winemaking, it is used to fill the empty space of the container in order to intensify the extraction of colouring agents and tannins (see also carbonic maceration). Oxidation protection is achieved by displacing air (oxygen) in containers and bottles. Furthermore, carbon dioxide is used with the help of a candle frit to remove off-flavours such as light sulphur fizz. And last but not least, carbon dioxide is also used for the neutralisation of alkaline cleaning solutions (as used for cleaning bottles and containers) with regard to cellar hygiene. See a list of all wine ingredients under total extract.
Glass: By © Nevit Dilmen, CC BY-SA 3.0, Link
Dry ice: By MarkS, CC BY-SA 3.0, Link
Graphic: By Rothwild - Own work, Public domain, Link
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