MrFoodScientist
Well-Known Member
Lately I've been really wondering about the alcohol content of a fermented soda. Then I realized that since the process is essentially skipping primary fermentation and going straight to carbonating with yeast in a bottle, the question would be applicable to general beer brewing as well.
It is generally assumed that carbonating sodas with yeast contributes a negligible amount of alcohol, but being I scientist, I really wanted to quantify "negligible" without sending samples to a lab.
Here are my thoughts, let's assume I want to carbonate to 3 volumes. Given that the definition of volumes already assumes STP, I'm going to convert that right to moles for a 12oz (355mL) bottle.
3 x 355mL = 1.065L
1.065L ÷ 22.4L/mol = .0475 mol CO2
In fermentation (ignoring intermediate products), each mol of glucose yields 2 mol of CO2 and 2 mol of ethanol.
So if that's the desired level of CO2, it's a closed system and that was the start of my fermentation, I can safely assume that there is an equal amount of ethanol; .0475 mol.
Molar mass of ethanol is 46g/mol, and specific gravity of pure ethanol is .789 (density is 789g/L).
.0475 mol etOH x 46g/mol =2.187g etOH
2.187g etOH ÷ 789g/L = .002772L or 2.77mL etOH
2.77mL ÷ 355mL = .0078 or 0.78% ABV
So is 0.78% ABV a negligible amount?
What I didn't account for was any extra CO2 to pressurize the headspace. I'm thinking that would be necessary to estimate the maximum possible ABV. Whether that's what really happens is anyone's guess.
My estimates are a bit higher than this thread, but the concept is the same:https://www.homebrewtalk.com/f39/does-alcohol-increase-during-bottle-conditioning-146189/
Has anyone seen this in their brewing? I'm open to criticism.
It is generally assumed that carbonating sodas with yeast contributes a negligible amount of alcohol, but being I scientist, I really wanted to quantify "negligible" without sending samples to a lab.
Here are my thoughts, let's assume I want to carbonate to 3 volumes. Given that the definition of volumes already assumes STP, I'm going to convert that right to moles for a 12oz (355mL) bottle.
3 x 355mL = 1.065L
1.065L ÷ 22.4L/mol = .0475 mol CO2
In fermentation (ignoring intermediate products), each mol of glucose yields 2 mol of CO2 and 2 mol of ethanol.
So if that's the desired level of CO2, it's a closed system and that was the start of my fermentation, I can safely assume that there is an equal amount of ethanol; .0475 mol.
Molar mass of ethanol is 46g/mol, and specific gravity of pure ethanol is .789 (density is 789g/L).
.0475 mol etOH x 46g/mol =2.187g etOH
2.187g etOH ÷ 789g/L = .002772L or 2.77mL etOH
2.77mL ÷ 355mL = .0078 or 0.78% ABV
So is 0.78% ABV a negligible amount?
What I didn't account for was any extra CO2 to pressurize the headspace. I'm thinking that would be necessary to estimate the maximum possible ABV. Whether that's what really happens is anyone's guess.
My estimates are a bit higher than this thread, but the concept is the same:https://www.homebrewtalk.com/f39/does-alcohol-increase-during-bottle-conditioning-146189/
Has anyone seen this in their brewing? I'm open to criticism.