Special process in the preparation of red wine. Other names are carbonic fermentation, carbon dioxide, carbon or whole-cluster maceration or maceration. It is also called fermentation because it starts during the maceration. The process was discovered more or less by accident in France in 1934. A team of researchers was investigating the possibilities of keeping table grapes as fresh as possible over a longer period of time. For this purpose, the grapes were kept under a carbon dioxide protective 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 mash fermentation. If carbon dioxide is present in a closed container, a very special kind of fermentation takes place. It takes place without the influence of yeasts within the berries. That is why it is often called intracellular fermentation.
During this process, the anthocyanins (pigments) of the skins are drawn off inwards. Up to 2% alcohol is formed in the berries. In the process, about one fifth of the sugar is consumed and the malic acid is reduced to half. Various substances such as acetaldehyde, amino acids, acetic acid ethyl ester (ethyl acetate), glycerine and methanol are produced in noticeably larger quantities than in the usual mash fermentation, in the case of glycerine even up to ten times the amount. The weight of the grapes causes the lowest berries to burst, and the added yeasts cause normal fermentation to begin in the must. However, the two processes can also take place in parallel. The result is light and less tannic, fruity wines that are intended for quick enjoyment.
There are different forms, which in detail are applied quite differently by producers depending on the region. Normally, the fermentation container is filled with whole grapes that have not been destemmed. This means that they remain intact, the grape skeleton is not removed and the berries are not crushed beforehand. The fermentation container must be free of oxygen, which is also achieved by pumping in carbon dioxide. The duration of carbonic acid maceration varies, some winemakers prefer one to 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 upwards, the effect is intensified. In Burgundy, there is a modified version in which the fermentation container is filled halfway with whole grapes and topped up with crushed grapes.
After about three to seven days, the must is drawn off and the remaining mash is pressed. Then the two musts are mixed and fermentation continues. This brings out the flavour and aroma of the grapes, while tannins and acids are much milder. Carbonic maceration is obligatory for Beaujolais Nouveau and other primeur wines. It is also used in the southern Rhône and in Languedoc-Roussillon. It is often blended with normally fermented wines. In Australia, Cab Mac is produced with it. In traditional mash fermentation, the grapes at the top also undergo this special fermentation. See also Macération semi-carbonique.
Complete lists 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 heading Winemaking. Comprehensive information on wine law can be found under the heading Wine Law.