When we talk about oxygen and oxidation in wine, it seems DO and CO2 go hand in hand. But I have chosen to give Cardon Dioxide its own blog. And rightfully so. Some of the best wines in the world are created with CO2 and it is something we use a lot of in winemaking. So, lets delve into the world of CO2 in the cellar.
What is Carbon Dioxide? “Carbon dioxide (chemical formula CO2) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalently double bonded to two oxygen atoms” -Wikipedia. It has a bad rap for being a nasty greenhouse gas, but when it comes to wine, it has so many roles in the winemaking process. Infact, it is present in all wines. We recognize it at 0.6g/L and still wines will have somewhere between 0.4-1.0gm/L while sparkling wines have upwards of 5.0gm/L.
CO2 is the byproduct of fermentation (yeast eating sugar and producing ethanol). This is what floods the cellar mid vintage and can punch you in the face if you get too close and friendly with the ferment. Once a wine has finished ferment, it will be saturated with CO2, and this will decrease with every movement around the cellar and at cold stabilization.
This is good news for any wines we do not want any ‘spritz’ in, say our shiraz. But if we want some in our Riesling to keep it looking bright and zingy, how do we get it back? We sparge just before bottling, dissolving CO2 into the wine, and displacing DO at the same time. We measure how much CO2 is in the wine using a Carbodoser and when we have the right amount we stop, and the wine is ready for bottling. How much will depend on style and variety, every winemaker is different.
A carbodoser is a quick and simple way to get a reading. All you need is a 100ml sample of wine, a thermometer and your carbodoser cylinder, cap and chart. See here to watch a video: how to use a Carbodoser.
CO2 is a very handy tool in the winemaker’s kit: at higher levels it can reduce the perception of bitterness and astringency in red and white wines, while enhancing perceived sweetness. We tested the Ara 0% last week in class. It had incredibly high levels- 2.6gm/L, which is very high for a white “wine”. We can only assume this was to try and cover all the acid and make up for the lack of aroma and flavour.
We routinely use it to protect our finished wines from oxidation by displacing O2. There are tank manufactures now harnessing ferment CO2 to create self-mixing tanks called Ganimedes, a very cool idea.
And let’s not forget the most important use of CO2: when we ferment in bottle, all that CO2 is captured and used to give us bubbles in the bottle. Thank you, Champagne!
So, there you have it. Carbon Dioxide in the cellar.
Better cellar handing everyone.
Dharmadhikari M. Use of Inert Gases (n.d) https://www.extension.iastate.edu/wine/files/page/files/useofinertgases1.pdf
Wine Australia, Dissolved carbon dioxide beliefs questioned by new research, (9 Nov 2018) https://www.wineaustralia.com/news/articles/dissolved-carbon-dioxide-beliefs-questioned
Safety Toolbox Talk: www.mbaa.com