Understanding CO2 in Cider

Key numbers for understanding carbon dioxide in cider.
Key numbers for understanding carbon dioxide in cider.

I have written various articles about carbon dioxide (CO2) in cider. I’ve provided details about what volumes CO2 means, how sugar is converted to CO2, how to force carbonate cider with a keg, and just how carbonation can impact your method for making hard cider (search the site for “CO2” or check out the tips page). As I was recently reading a research paper it noted how the US government increased the allowable amount of CO2 in hard cider to 0.64 grams per 100ml or 6.4grams per liter in 2017. Most scientific papers that I read use grams per liter or grams per 100ml when discussing CO2. The problem is that this number doesn’t mean much to me. It’s hard for me to visualize what 0.64 grams of CO2 would look like in 100 ml of cider. If you tell me there is 3.26 liters of CO2 in every liter of cider, I can understand that much easier. That made me realize I needed to provide a chart that showed how volumes CO2 related to grams CO2 per liter of cider. It also made me realize I should include a few other key numbers. These numbers include the specific gravity and amount of sugar that would be needed to create that amount of CO2. I also noted how much additional alcohol, as a %ABV, would be generated if you fermented that amount of sugar.

This chart is really just a reference to help you understand the conversion of volumes CO2 to grams CO2 per liter. The equation is straight forward (g/l = volumes CO2 x 1.96, which is the standard density if CO2). The chart isn’t intended to define the amount of sugar to add for bottle conditioning. You could use it for that but if you do, you need to remember that your cider will naturally retain about 0.85 volumes CO2 (1.67 grams CO2/liter). So, if you want to stay under the legal level of CO2 to qualify for the lower tax on hard cider in the US, you need to subtract the 0.85 from your target. If you wanted the legal limit of 6.4 grams CO2 / liter, you would only add 9.7 grams sugar per liter to reach it (3.26 volumes CO2 needs 13.1 grams sugar / liter less the 3.4 grams sugar per liter needed for the 0.85 volumes already suspended from fermenting). I’ve highlighted the normal residual volumes CO2, 0.85, in blue and the US classification amount in orange. Lastly, notice how a little sugar can be turned into a large amount of CO2.

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Want more details about making and enjoying cider, check out these posts.

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