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Carbonation epiphany

Have to say that I’ve been brewing for over six years and feel kind of rediculous, maybe a little embarrassed, for not thinking of this much sooner, lIke as in before i evendors carboated my first batch. As a scientist with a good amount of chemistry in my background, this should have become apparent. Anyone seeing any problems with the following logic?

I for some reason always thought to get the carbonation level I entered the Vol of CO2 desired and the temp of the beer while carbonating. It now makes sense to me that x grams of sugar will yield y grams of CO2 regardless of temperature. The difference in how much gets absorbed will depend on storage temperature. Meaning ify fridge is 46 degrees I should use that number in my calculations. It all makes sense now. It also explains a lot on why I had problems keeping carbonation in my keg that had no temperature. I feel rediculous that it took so long to figure that out but it seems clear as day now.

Guess I should think about returning that degree :wink:

Almost, but not quite…

The temperature is needed to estimate the amount of CO2 that is already dissolved in the beer. At the end of active fermentation, the beer is pretty much saturated with CO2. As I’m sure you know, the amount of CO2 that can be held in solution is a function of temperature and pressure. This is all at atmospheric pressure, so take that out of the equation. The hotter the beer, the less CO2 in solution, and the colder the more CO2 in solution.

The problem is that by the time CO2 is no longer being produced (i.e., the end of active fermentation), the hottest temperature the beer hits will determine the maximum amount of CO2 that will be dissolved. Cooling it down does not dissolve more CO2, as there is not any more CO2 being produced.

So the calculators are wrong. You don’t use the current temperature of the beer - you use the highest temperature of the beer once active fermentation is complete. But that’s complicated, so the calculators tell you to do something simple, which is to use current temperature.

For example, if the highest temperature after active fermentation means there’s 0.5 volumes dissolved in the beer (just pulling that number out of the air…) and you want to carbonate to 2.5 volumes, you need to add enough sugar to give you an additional 2 volumes of CO2 that will dissolve as pressure inside the bottle and keg rises.

The problem with these calculators, is if you cold crash or lager your beer, and then use that temperature in the calculator, you’ll get an artificially high residual CO2 in the beer, and will end up not adding enough sugar to get the carbonation you want.



Ah I always forget about residual CO2. Seeing as to how there is a 33% increase in the amount of sugar needed to reach the same Vol of CO2 at 44° to 68° I could see that being an issue.

It’s been awhile since I’ve actually done the calculations by hand and. Assuming however that fermentation temperatures at all times stay within a few degrees, one should be able to dial in an amount that will yield consistent results.

I’ve been getting much more consistent results ever since abandoning the 5oz corn sugar no matter what. Now it’s all about getting a correct (at least really close) volume and actually weighing the sugar. Excited to try kegging again now that I have a beer fridge. Still need a new poppit valve though

I’m still confused about the keg without any temperature… Reasonable impossible? Also as beer is pushed out of the keg, won’t that effect the amount of gas that can escape, albeit cold? So carbbing in the keg isn’t a constant, more of a variable? I’m lucky I use the CO2 tank… :neutral_face: Sneezles61

The keg carbing was on gas. More of a side note than actually on topic. Should have been clearer. My bad

My thought on the keg is that more co2 will leave solution when half full at 75 which was storage temp for the keg then it would sitting in ice which was my way of serving. I am guessing carbonation will stay more consistent if carbonated at a specific temperature and actually held there.

Since the co2 would not all instantly go back into solution, everytime I had to vent to serving pressure I would get less and less carbonation. I suppose one fix would be to drain a keg in one sitting :grin:

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Yep, in the keg you’re now increasing pressure. So as you dispense some, more CO2 flows into the keg to maintain pressure, so you don’t lose carb. If you took it off the gas, you could still dispense but the CO2 will start coming out of solution due to the lower pressure, until everything stabilized to atmospheric pressure and you couldn’t dispense any more.

If you take it off the gas and bring it up to temperature, the CO2 in the headspace will expand, increasing pressure and keeping most of the CO2 in the beer. Depending on the amount of headspace you may lose some carb but it should pretty much be stable due to the closed system.

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