Calculation for %ABV Increase during Bottle Conditioning

[MrFoodScientist]

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.

 

[WoodlandBrew]

I've done the same analysis another way around here:
http://woodlandbrew.blogspot.com/2012/12/abv-from-priming-sugar.html

5oz of sugar in 5 gallons yields a gravity of 1.003. Fermented dry that yields 0.4% ABV.

I checked all your math, and looked up all the constants and what you have looks correct, but it's off by a factor of two from what I would expect.

 

[Beergazzi]

As impressive as MrFoodScientist's post was, well, mine is going to be god awful simple (cause I ain't into dat dere fancy math ) to draw a similar conclusion.

Go to your favorite recipe calculator, I am using BrewR on my phone since its handy. All I did to calculate this was to add as an ingredient whatever the 'sugar' was I used to bottle, as a 'fermentable' and noted the affect on abv.

For my 5gal stout, I used 2.5oz of corn sugar. According to the recipe, this increases abv by .2% . I added 2.6oz of honey to a 2.5gallon cream ale at bottling, and according to this software, thats worth .2% as well.

certainly this isn't alot, but not negligible either.

Basically, after running this through the recipes and calculating the Co2 from 2.0-3.0, it will yield 2-3% alcohol. I'd say if you are shoot for less than 2.5 volumes of carbonation its .2%abv, and over 2.5 vols is .3% abv.

 

[highgravitybacon]

It's not just abv, but body of the finished product that changes. I noticed this when carbonating a rather small (1.038) beer that fermented dry (1.005) to a high level-3.5 volumes. It took about 175 grams of sucrose. This amounted to 5% fermentables by weight which is not by any means an insignificant amount. The beer was considerably drier than anticipated due in part to the co2, but also the sugar.

In the future, I will either reduce the starting gravity on a small beer to account for this, reduce the simple sugars on a bigger beer, or use unfermented wort to prime with which will leave the exact same ratio of malt/hops in the finished beer. For some reason, it bothers me to just toss aside the role of the priming sugar as if it didn't matter.

 

[WoodlandBrew]

As impressive as MrFoodScientist's post was, well, mine is going to be god awful simple (cause I ain't into dat dere fancy math ) to draw a similar conclusion.

Go to your favorite recipe calculator, I am using BrewR on my phone since its handy. All I did to calculate this was to add as an ingredient whatever the 'sugar' was I used to bottle, as a 'fermentable' and noted the affect on abv.

For my 5gal stout, I used 2.5oz of corn sugar. According to the recipe, this increases abv by .2% . I added 2.6oz of honey to a 2.5gallon cream ale at bottling, and according to this software, thats worth .2% as well.

certainly this isn't alot, but not negligible either.

Basically, after running this through the recipes and calculating the Co2 from 2.0-3.0, it will yield 2-3% alcohol. I'd say if you are shoot for less than 2.5 volumes of carbonation its .2%abv, and over 2.5 vols is .3% abv.

This is a reasonable approach to get an estimate, but most calculators assume 75% fermentability but sugar ferments close to 100%

 

[Beergazzi]

This is a reasonable approach to get an estimate, but most calculators assume 75% fermentability but sugar ferments close to 100%

Really? I assumed they built into their 'ingredients' some more specific specs. At least for something like 'corn sugar'.

Regardless, if true, then a .2-.3% increase in a calculator, would be like a .3-.4% increase in abv, makes it even more worth calculating recipes in anticipation of this (if bottle carbing)

 

[WoodlandBrew]

Really? I assumed they built into their 'ingredients' some more specific specs. At least for something like 'corn sugar'.

Regardless, if true, then a .2-.3% increase in a calculator, would be like a .3-.4% increase in abv, makes it even more worth calculating recipes in anticipation of this (if bottle carbing)

Unfortunately yes it's true, but some calculators, like the one on brewers friend, have a place for you to add a "custom" attenuation.

What I do to keep the ABV the same is to mix enough water with the sugar when priming to match the OG of the beer.

You can read more about it here:
http://woodlandbrew.blogspot.com/2013/04/easy-priming-sugar.html

 

[highgravitybacon]

Unfortunately yes it's true, but some calculators, like the one on brewers friend, have a place for you to add a "custom" attenuation.

What I do to keep the ABV the same is to mix enough water with the sugar when priming to match the OG of the beer.

You can read more about it here:
http://woodlandbrew.blogspot.com/2013/04/easy-priming-sugar.html

You will dilute and hop and malt character then, which depending on how much you add (probably about a liter or 1.5 liters maybe?). This will keep the abv in line but at the expense of the other characteristics.

 

[WoodlandBrew]

You will dilute and hop and malt character then, which depending on how much you add (probably about a liter or 1.5 liters maybe?). This will keep the abv in line but at the expense of the other characteristics.

Exactly. It's normally about 1 litter in 19 which is a 5% change. If you were really concerned about malt character you could use DME. Hops changing by 5% will go unnoticed by most people.

 

[highgravitybacon]

Exactly. It's normally about 1 litter in 19 which is a 5% change. If you were really concerned about malt character you could use DME. Hops changing by 5% will go unnoticed by most people.

You could brew a neutral wort of 1.050 from pale malt, hopped to 15 ibu with hop extract or magnum and freeze it. Then prime with that. I have never done this, but it seems like it would be a universal priming solution.

 

[WoodlandBrew]

You could brew a neutral wort of 1.050 from pale malt, hopped to 15 ibu with hop extract or magnum and freeze it. Then prime with that. I have never done this, but it seems like it would be a universal priming solution.

That's similar to a German technique, of which the name escapes me now. Part of the initial wort is reserved unfermented to be used for primining. It's a good way to make sure the beer is insignificantly changed by priming. Although I find the method I use to be easier and does not change the beer much according to my pallet.

(Back to the OPs original question)

I think your calculations laid out in the first post are spot on. The 5oz in 5 gallons to archive 3 volumes of carbonation assumes that there is some carbon dioxide in solution from fermentation. When making soda there is no initial carbon dioxide in solution. The amount you have calculated is reasonable.