Current Beer Temp in Priming Calculators

[Epos7]

I'm drinking my first batch of beer at the moment. When I bottled I used one of the priming calculators, and entered the temperature of the beer as a few degrees warmer than what I had cold crashed it to, thinking the beer would warm up a little bit before I got it into bottles.

The beer is good, but a little on the flat side. I'm going to bump up my priming sugar amount a little bit next time.

I understand the logic behind the calculators is that colder beer can hold more CO2 in solution, but where is this CO2 coming from? The difference in priming sugar, per most calculators, is several ounces between cold crashed beer and room temperature beer. When it's fermenting, most of the CO2 is going to get pushed out the airlock, only leaving what can fit in the headspace. Once cold crashed, that CO2 in the headspace, could be pulled back into the beer, but the volume of the headspace is significantly smaller than the volume of the beer.

When I cold crashed, my fermenter sucked some of the Star San out of my airlock back into the fermenter. It probably pulled in some oxygen from outside the fermenter as well.

The difference in recommended priming sugar amount is about 1.5oz between cold crash temps and room temps. 1.5oz of priming sugar on its own provides 1.4 volumes of CO2. I don't see there being 1.4 volumes of CO2 left in the headspace - what am I missing here?

 

[Qhrumphf]

You're correct. I would expect a *slight* increase in dissolved CO2 from cold crashing, but I wouldn't expect it to be significant. Any CO2 build up greater than 1atm plus whatever pressure from the airlock is going to escape through the airlock. Plus if you open the lid/bung/whatever, you're going to have air mixing with that CO2 anyway. Plus it would have to reabsorb. Those calculators are going off of what remains at that temperature- if you ferment 50F and stay at 50F without a diacetyl rest or anything, I would expect it to be quite accurate for that temp. But I don't think cold crashing really factors in to the equation. Now, someone who knows their physics better than I could probably give you a better way to approximate, but I'd sooner go with whatever the warmest temp the beer reached was, and if cooled down below that, pad it a little bit for absorption of whatever residual there is.

 

[CJ-3]

You will find your beers will carbonate correctly if you enter the highest temperature your beer reached during the fermentation process as opposed to the temperature it is at after cold crashing.

 

[day_trippr]

You will find your beers will carbonate correctly if you enter the highest temperature your beer reached during the fermentation process as opposed to the temperature it is at after cold crashing.

Most accurate is to use the warmest post-fermentation/pre-crash temperature.
Using the highest temperature including the throes of fermentation will induce an error, because as the temperature drops to a stable level the CO2 level in the beer actually rises 'til fermentation is complete...

Cheers!

 

[EPbrew]

You will find your beers will carbonate correctly if you enter the highest temperature your beer reached during the fermentation process as opposed to the temperature it is at after cold crashing.

I read this recently and haven't had any problems since.
https://www.homebrewsupply.com/lear...ium=email&mc_eid=a19b3816fd&mc_cid=6053904675

 

[CJ-3]

Most accurate is to use the warmest post-fermentation/pre-crash temperature.
Using the highest temperature including the throes of fermentation will induce an error, because as the temperature drops to a stable level the CO2 level in the beer actually rises 'til fermentation is complete...

Cheers!

You are correct. I should have stated it that way.

 

[Epos7]

Thanks all. A few degrees over my cold crash temperature gave me 2.3oz of corn sugar, but it looks like I should have used ~4.5. Now I know I'm not crazy and why my beer is a bit flat.

 

[catdaddy66]

I read this recently and haven't had any problems since.
https://www.homebrewsupply.com/lear...ium=email&mc_eid=a19b3816fd&mc_cid=6053904675

Awesome link, thanks!

 

[doug293cz]

I'm drinking my first batch of beer at the moment. When I bottled I used one of the priming calculators, and entered the temperature of the beer as a few degrees warmer than what I had cold crashed it to, thinking the beer would warm up a little bit before I got it into bottles.

The beer is good, but a little on the flat side. I'm going to bump up my priming sugar amount a little bit next time.

I understand the logic behind the calculators is that colder beer can hold more CO2 in solution, but where is this CO2 coming from? The difference in priming sugar, per most calculators, is several ounces between cold crashed beer and room temperature beer. When it's fermenting, most of the CO2 is going to get pushed out the airlock, only leaving what can fit in the headspace. Once cold crashed, that CO2 in the headspace, could be pulled back into the beer, but the volume of the headspace is significantly smaller than the volume of the beer.

When I cold crashed, my fermenter sucked some of the Star San out of my airlock back into the fermenter. It probably pulled in some oxygen from outside the fermenter as well.

The difference in recommended priming sugar amount is about 1.5oz between cold crash temps and room temps. 1.5oz of priming sugar on its own provides 1.4 volumes of CO2. I don't see there being 1.4 volumes of CO2 left in the headspace - what am I missing here?

You're not missing anything. The reabsorption of CO2 during cold crashing is pretty minimal. The worst case reabsorption for a 5:1 beer volume to headspace volume ratio, and crashing from 20˚C (68˚F) to 1˚C (33.8˚F) is about 0.07 volumes of CO2, and that would probably take a week or more of cold crashing.

I presented the full blown cold crashing analysis in this post some time ago. Note that the numbers in that post are a little off, as I didn't use the best equation for dissolved CO2 as a function of temp and pressure, but the conclusions are still valid (the post is too old for me to edit .) The 0.07 volume worst case above is based on the "best" available equation for CO2 content.

The residual CO2 comes from fermentation. For each molecule of glucose "eaten" by the yeast, one molecule of ethanol and one molecule of CO2 is created. Most of this escapes the fermenter thru the airlock, but the beer will retain an equilibrium amount of CO2 based on the headspace CO2 partial pressure and the temperature of the beer. At the end of fermentation the CO2 partial pressure is 1 atmosphere (14.7 psi.) @EPbrew linked (in a previous post) to an article that gives some values of residual CO2 content vs. temperature.

You're correct. I would expect a *slight* increase in dissolved CO2 from cold crashing, but I wouldn't expect it to be significant. Any CO2 build up greater than 1atm plus whatever pressure from the airlock is going to escape through the airlock. Plus if you open the lid/bung/whatever, you're going to have air mixing with that CO2 anyway. Plus it would have to reabsorb. Those calculators are going off of what remains at that temperature- if you ferment 50F and stay at 50F without a diacetyl rest or anything, I would expect it to be quite accurate for that temp. But I don't think cold crashing really factors in to the equation. Now, someone who knows their physics better than I could probably give you a better way to approximate, but I'd sooner go with whatever the warmest temp the beer reached was, and if cooled down below that, pad it a little bit for absorption of whatever residual there is.

Been there, done that. See the link above.

Brew on