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Corn sugar calculation

doldenburg

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Jun 1, 2004
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Brad,

I wonder if you could share your method for calculating how much corn sugar I need to carbonate to a certain level.  When I calculate it by hand, My results are slightly different from yours.  Here is my example:

- I want 3 volumes of carbonation for 20 L at 20 deg. C.
- 1 volume = 1.8 g/L, so I want 5.4 g/L of C02
- Total CO2 I want dissolved is 5.4*20 = 108g
- at 20 degrees, .862 volumes, or 1.55 g/L should already be dissolved
- So... I already have 1.55*20=31g dissolved, meaning I want to add 77g
- for each gram of CO2 I want, I need to ferment 2.08g of glucose
- to add 77g, I need to add 160.2 g of glucose
- Therefore, I need 160.2 g of corn sugar

Beersmith says I need 171.7 g of corn sugar.

Can you tell what the difference is between my answer and yours?  Are you accounting for the CO2 that remains in the headspace of the bottle or keg?  If so, how do you factor that in?

Thanks,
David
 
David,
 My calculations use a curve fit -

 sugar_g = 15.195 * vol_gals * (vols_desired - 3.03 + .05 * temp_f - .000265*temp^2)

 One significant variable is the fermentability of the corn sugar, which can very depending on the refining of the sugar.

 In fact, that factor alone could easily account for more than the variance you are seeing here.

Cheers!
Brad
 
Brad,

Thanks so much for sharing that.  I used it to determine that I should count on only 93.3% of the sugar fermenting.  Now our formulas are the same.

I also used it to come up with a formula for how much CO2 is already dissolved prior to priming at a given temperature:

carb_v = 3.03-0.05 * temp_f + 0.000265 * temp_f^2
 
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