I know yeast ferments sugars into alcohol at a predictable rate, but is the same is true for carbon dioxide? Since I know the amount of sugars fermented though my gravity readings, shouldn't it be possible to calculate C02 yield? Does anyone know a formula for doing this?
I ask purely out of curiosity.
Topic calculations fermentation homebrew
Category Mac
I believe the weight of CO2 expelled pretty much exactly explains the change in weight and so in specific gravity. My 23 litre (30 bottle) wine bucket started with an SG of 1.074 so would have weighed 24.7kg (54.4 lbs). If it finishes at an SG of 1.000, it will then weigh 23kg so will have lost 1.7kg (3.7 lbs) of CO2. Volume is slightly trickier. One Mol of gas occupies 24 litres. One Mol of CO2 is 44g, so my 1.7kg is 38 Mol or 927 L - about a cubic metre (or yard).
Calculate by reduction of the sugar content. i.e if sugar content is reduced by x amount then CO2 generated will be x * volume of vessel* density of liquid in the vessel *44/46
I too was curious about this the other day. Turns out for five gallons/18.9 L of 1.060 wort at 75% apparent attenuation, 449.1 L/ 15.86 cubic feet/ 118.64 gal of CO2 is produced (standard temperature and pressure. This amounts to 0.88 kg/ 1.94 lb of CO2!
I have a few charts for different gravities and apparent attenuations at my blog post about it. I also explain all of the calculations behind it too, if you're curious. - Dennis, Life Fermented Blog
There's so called Balling formula to calculate "accurate enough" amounts of alcohol, CO2 and yeast mass produced during fermentation. This formula is used in all EU countries to calculate excise duty:
2.0665 gms extract in wort make 1 gm of alcohol, 0.9565 gm CO2 and 0.11 gm yeast mass
Calculate weight of extract that has been consumed by yeast then equate it with above values. For example, fermentation of 100 hL wort of 12 Plato to 3 Plato produces ~441.9 kgms CO2.
One person has measured CO2 production and found that he got 25 gal. of CO2 for one gal. of 1.060 beer. Another person who has measured it has written "Looking at the ratio of alcohol and CO2 atomic weights in the fermentatin equation suggests that for every pound of alcohol you should get 1.045 lbs of CO2. The above brew (in the example he was writing about) is 6.6% ABV or 5.28% ABW. In 40 lbs of beer, that's 2.1 lbs of alcohol, meaning 2.2 lbs of CO2. Or 133 gallons. This jives with the amount I would collect for a beer of that strength, though my measurements are pretty approximate."
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