Pressure fermentation- calculating priming sugar

[SMD]

I’ve got a lager fermenting under pressure in a keg right now. I built a spunding valve and I’ve got it set right at 12 PSI. When fermentation is done I want to bottle this lager, however since it’s under pressure now, is there a way to know how much CO2 could potentially be in the beer already? Im afraid if I prime like a regular fermentation I’ll end up with bottle bombs.

 

[doug293cz]

At what temperature will you finish your fermentation (before any cold crash?) Use that temp and 12 psi to look up the carb level in your favorite carbonation chart. Then, subtract that carbonation level from your final target carbonation level, this will give you the number of volumes of carb you need to add with priming sugar (Priming Delta.)

1 volume of carbonation is equal to 0.264 oz/gal of CO2. 1 oz of sucrose (table sugar) creates 0.514 oz of CO2, and 1 oz of corn sugar creates 0.444 oz of CO2. Now calculate your required priming sugar as:

​

Weight of Sucrose = Beer Vol [gal] * Priming Delta * 0.264 [oz/gal] / 0.514 [oz/oz]​

Weight of Corn Sugar = Beer Vol [gal] * Priming Delta * 0.264 [oz/gal] / 0.444 [oz/oz]​

​

I recommend that you cold crash at the end of fermentation, and bottle cold, to minimize CO2 evolution while you are bottling. If your pressure drops to 0 psi while cold crashing, stop the cold crash to avoid damage to your fermentation vessel.

Brew on