Winetech Technical Yearbook 2022

OCTOBER

CARBONIC MACERATION

CARBONIC MACERATION IS THE STORAGE OF WHOLE GRAPE BUNCHES IN AN INERT ATMOSPHERE OF CARBON DIOXIDE. THE CARBON DIOXIDE CAN BE GENERATED BY YEAST FERMENTING JUICE OR ADDED CARBON DIOXIDE. THE ATMOSPHERE MUST BE FILLED WITH CARBON DIOXIDE TO PREVENT ACETIC SPOILAGE IN AEROBIC CONDITIONS. UNLIKE YEAST FERMENTATION, OXYGEN IS INTERNALLY USED, AND AN INTRACELLULAR ENZYMATIC FERMENTATION OCCURS UNTIL THE BERRY DIES. THE DEATH IS CAUSED BY THE FORMED ALCOHOL OR WHEN THE BERRIES ARE BROKEN. A UNIQUE AROMA FORMATION, SOMETIMES DESCRIBED AS BUBBLE GUM, RESULTS FROM THIS MACERATION PERIOD.

BY CHARL THERON

IZELLE VAN BLERK, KWV

REASONS FOR CARBONIC MACERATION Carbonic maceration is globally applied and Pinot noir, Grenache and Shiraz are amongst the varieties used. It seems, however, that Cabernet Sauvignon grapes are not suitable. In France, it was Gamay that made the process known. It is a thin-skinned grape with slight colour, tannins and prominent character, which needs carbonic maceration to enhance the flavour and mouthfeel of the wine. Pinot noir also has limited natural colour and tannins in certain Australian regions. Clones like Dijon 114 and 115 have compact bunches, which do not destem well, and it may be more feasible to apply whole-bunch fermentation. In some cases, only partial whole bunch fermentation is applied and used together with conventional skin contact extraction processes. This may lead to a green tannins character if the stems are not ripe enough and over-extraction occurs. Putting destemmed and whole bunches together for carbonic maceration is not advised, but rather blend ing the resulting wines if preferred. IDEAL CONDITIONS FOR CARBONIC MACERATION When complete whole-bunch fermentation is applied, clean and sound grapes with relatively ripe stems to prevent capsicum char acters are preferred. The grapes should also be picked during the warmer times of the day. It seems that cooler seasons are better for carbonic maceration. This is due to the berry ripeness being more parallel to the phenological ripeness of the stems, compared to warm seasons when the berry ripeness tends to be faster. APPLICATION OF CARBONIC MACERATION When complete whole-bunch fermentation is applied, an inert carbon dioxide atmosphere must be created. A healthy alcohol fer ment is started and topped up with whole bunches while carbon dioxide is added to ensure an inert carbon dioxide atmosphere. The carbon dioxide must be added abundantly to prevent an aer obic atmosphere for spoilage bacteria. Dry ice on the top of the whole bunches and a plastic cover of the fermenter also add to the creation of inert conditions. It is left for about three days before the cover is removed, and the fermenting juice is drawn from the bottom and added to the top. The rack-and-return process of fermenting juice is done once or twice daily before the fermenter is covered again. When sufficient carbon dioxide has been formed, the fermenter need not be kept closed anymore, but the rack-and-return practice is continued until the berries are broken. More sugar is released into the juice, and the carbonic maceration is complemented by conventional alcoholic fermentation.

The stage of pressing the skins is important.

The stage of skin pressing is important because the increasing alcohol formed will extract more tannins from the stems, which may be undesirable. The degree to which carbonic maceration will occur will determine the aroma concentration attributed to it. Spontaneous malolactic fermentation tends to occur at the end of the process, which may take between 10 days and three weeks. This depends on the initial temperature and stem quality. It is essential to keep the ferment warm, and an initial temperature of 20 - 22°C is beneficial to initiate the fermentation. After pressing, a temperature of up to 32°C is maintained to ensure that the sugar released from the skins is completely fer mented. The pH of the fermenting juice must be checked because the extraction of potassium during the process may increase the pH of the fermenting juice. REFERENCES https://www.wineland.co.za/carbonic-maceration/

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WINETECH TECHNICAL YEARBOOK 2022