Priming sugar equations and pre-existing CO2

[TexasLonghorn]

Hi all,

I was doing some reading on bottling and priming sugar equations as I am trying to be a little more exacting on my volumes of CO2 than I have in the past. For this batch, I'm going for about 2.5 volumes of CO2. I've found several calculators, and they all give the same answer as to how much sugar to use. I've also found equations which yield the same answer (about 4.24 oz of corn sugar for 4.75 gallons of 70 degree F beer). I'm using this equation from Zymurgy: PS (grams) = 15.195 Vb ( CD - 3.0378 + .050062 * T - .00026555 * T * T ). Vb is beer volume and CD is desired volumes of CO2. I don't know how this equation was derived (if someone knows, that would be great to see).

However, I came across this article: Link which talks about accounting for the volumes of CO2 already in the beer from fermentation. My question is: does the above equation already account for the CO2 in the beer prior to priming, or should my CD in the above equation be (2.5 - pre-existing CO2) instead of just 2.5?

Thanks for any help.

 

[TexasLonghorn]

A little more time wasted at work and I have my answer. For those interested, the following link discusses the above formula (which does indeed account for initial volumes from fermentation): Math In Mash

 

[mcnewcp]

I just now stumbled upon this thread and you asked the exact same question I had and then answered it. Well done!

 

[Orval]

A little more time wasted at work and I have my answer. For those interested, the following link discusses the above formula (which does indeed account for initial volumes from fermentation): Math In Mash

Thanks a lot... Nice pdf which covers many important topics with tables and equations...