CO₂: The Winemaker’s Invisible Sidekick
CO₂, or carbon dioxide, is a simple yet fascinating molecule made of one carbon atom bonded to two oxygen atoms. Though it is invisible and often overlooked, it plays a surprisingly big role in winemaking, quietly influencing both the process and the final product. During fermentation, yeast converts sugar in the grapes into alcohol and, in doing so, releases CO₂ in tiny, playful bubbles. These bubbles are not just for show. They can sit over the wine like a soft, invisible blanket, while some CO₂ remains dissolved in the wine, giving it a subtle lift, a touch of sparkle and a hint of crispness or lively zing depending on how much is present.
Winemakers can also use CO₂ intentionally to protect wine from oxygen. Whether used as a gas or in the form of dry ice, it can help create a protective layer around grapes, juice and wine. This helps reduce oxidation and can help keep the wine tasting fresh, vibrant and full of flavour. CO₂ can also be used when preparing tanks, bottles and other equipment, helping to remove oxygen before wine comes into contact with them.
CO₂ has another fascinating role in winemaking through a technique called carbonic maceration. Here, whole grapes are placed into an environment containing CO₂. Instead of the grapes immediately undergoing the usual fermentation process, changes begin to happen inside the intact berries. This can create wines with distinctive fresh and fruity characters, often giving juicy red fruit flavours and a particularly vibrant style of wine.
And then, of course, there is sparkling wine. Those beautiful streams of bubbles in your glass are CO₂ too. In traditional method sparkling wine, the CO₂ is produced naturally during a second fermentation that takes place inside the sealed bottle. Because the bottle is sealed, the gas cannot simply escape and instead becomes dissolved in the wine. When the bottle is opened, the pressure drops and the CO₂ comes out of the wine, creating the bubbles we see and feel.
Sparkling wine made using the tank method works in a similar way, except the second fermentation takes place inside a sealed pressure tank rather than individual bottles. There is also a much simpler method where CO₂ is directly added to wine to create the bubbles.
Even still wines can contain some dissolved CO₂. Small amounts can add freshness and a lively sensation to the palate. You may notice this particularly in young white and rosé wines, where a little bit of dissolved CO₂ can make the wine feel brighter and more energetic.
But CO₂ can also be one of the most dangerous things in a winery. During fermentation, huge amounts of CO₂ can be produced. Because it is invisible, you cannot see when it has accumulated, and in areas with poor ventilation it can build up, particularly around fermentation vessels and in low or enclosed spaces. As CO₂ increases, it can reduce the amount of oxygen available to breathe, potentially causing dizziness, unconsciousness and even death. This is why good ventilation, monitoring and proper safety procedures are incredibly important during vintage.
CO₂ is even becoming part of conversations around sustainability in winemaking. Some larger wineries are looking at ways to capture the CO₂ produced during fermentation and put it to use elsewhere in the winery. Instead of simply allowing it to escape, capturing and reusing it could turn something that was once considered a waste product into a useful part of the winemaking process.
From its tiny molecular structure to its surprisingly big influence on fermentation, wine protection, sparkling wine, flavour and even winery safety, CO₂ really is one of the unsung heroes of winemaking. It may be invisible, but its impact certainly isn't. 🍷✨