Special procedure for red wine making. Other designations are carbonaceous fermentation, carbonic acid, carbon dioxide, carbon or whole grape maceration or maceration. It is also called fermentation because it starts already during the maceration. The process was discovered more or less by chance in France in 1934. A team of researchers investigated the possibilities of keeping table grapes as fresh as possible over a longer period of time. To do this, the grapes were kept under a carbon dioxide inert gas cover at 0 °C. After two months they began to ferment. They were processed into wine that was lighter, more fragrant and less tannic than with conventional maceration. When carbon dioxide is present in a closed container, a very special type of fermentation takes place. It takes place without the action of yeasts inside the berries. This is why it is often referred to as intracellular fermentation.
During this process, the anthocyanins (colorants) of the skins are drawn off inwards. Up to 2% alcohol is formed in the berries. This process consumes about one fifth of the sugar and reduces malic acid to half. Various substances such as acetaldehyde, amino acids, acetic acid ethyl ester (ethyl acetate), glycerol and methanol are produced in noticeably larger quantities than in the usual mash fermentation, in the case of glycerol up to ten times the amount. Due to the weight of the grapes, the lowest lying berries burst and due to added yeasts, the normal fermentation starts in the must. However, the two processes can also take place in parallel. Light and less tannic, fruity wines are produced, which are intended for quick enjoyment.
There are different forms, which are used quite differently by the producers depending on the region. Usually the fermentation tank is filled with whole grapes that have not been destemmed. They remain intact, the grape skeleton is not removed and the berries are not crushed beforehand. The fermentation tank must be oxygen-free, which is also achieved by pumping in carbon dioxide. The duration of the carbonic maceration varies, some winemakers prefer one or two days, others up to a week. As a rule of thumb: the riper the grapes, the shorter the process. If the fermenting must that forms at the bottom is pumped up, the effect is intensified. In Burgundy there is a modified variant, in which the fermentation tank is filled up to half with whole grapes and filled with ground grapes.
After about three to seven days the must is drawn off and the remaining mash is pressed. Then the two musts are blended and fermentation continues. This brings out the taste and fragrance of the grapes, while tannins and acids are much milder. The carbonic maceration is obligatory for Beaujolais Nouveau and other Primeur wines. It is also used on the southern Rhône and in Languedoc-Roussillon. It is also often blended with normally fermented wines. In Australia the Cab Mac is produced with it. Also with the traditional maceration, the grapes on top undergo this special fermentation. See also under Macération semi-carbonique.
A complete list of the numerous vinification measures and cellar techniques, as well as the types of wine, sparkling wine and distillate regulated by wine law, can be found under the keyword vinification. Comprehensive information on wine law can be found under the keyword wine law.