Cold crashing with a CCG

IMO the beer will be not care if the CO2 was from natural fermentation or a bottle (Reinheitsgebot be damned). The accountability of the dissolved CO2 (residual carbon dioxide) is temperature and time related and yes it can be significant. Here's a decent discussion on the subject and a calc that shows the difference in temps: https://www.brewersfriend.com/beer-priming-calculator/

Not sure I'm following your point here, but final grav measurements can be at any reasonable beer temp with later being preferred over early . . . you know, just to be sure. If really finished it would be the same at top of diacetyl rest or bottom of CC. Your concern here is how long the beer was chilled and how much of the additional CO2 (residual) was dissolved into the brew.

 

Yes.

From a naturally collected bladder full of CO2? Or a couple of PSI from a tank for a couple of days? Either way, no, the effect wouldn't be significant. Maybe a tenth of a volume or so?

 

Why would you want to raise the temp to bottle? Why not just bottle at CC temp? Either would work, but by raising you're dumping out some CO2 which you have to re-infuse. I regularly bottle (add priming sugar) at keg temps.

The problem in computing residual carbon dioxide (acknowledged in the link) is the uncertainty of equilibrium of the gas as you change temps. If you ferm'ed, rested, and packaged all at say 66 the calcs should be right on. But when you raise the temp, how long until it loses all that's predicted? When you cold crash CO2 will be reintroduced, but how long does it take to stabilize? There's some difficult math that actually addresses these problems plus lots of real-world variables that are cumbersome. Example: the dimensions of your fermenter (unitank) effects how fast gas moves in and out . . . a long neck bottle will off-gas slower than if you poured the contents into a large pan.

My guess, (and it really is a guess) is if you leave it cold for 48 hours it will hit the prediction in the calculator. Residual CO2 at 40F is ~1.5v, while at 70 is ~0.8v . . . that's too big of difference to ignore. Maybe keep good notes and refine your assumptions. Or just put a really big condum on the fermenter with XX points to go:

 

That additional "residual" CO2 has to come from somewhere. In a closed system, there's not enough headspace CO2 to provide that extra 0.7 volumes at equilibrium. A collection bladder (like the cold crash guardian) won't have enough CO2 to provide that, at least not the way @riptorn plans to use it. An extra 2 PSI of (absolute) tank pressure will provide more than the guardian, but even if allowed to reach equilibrium (like after a couple weeks) will only provide ~0.184 additional volumes at 40F. Less than that in the couple of days needed to cold crash.

 

I'd like to see those comps . . .

 

Pick your favorite force carbonation calculator. Start with a low-ish baseline value for CO2 volumes and note the pressure required at 40F. Tweak the CO2 volumes until the pressure required is 2 PSI higher than at the baseline. Subtract the baseline volumes from the tweaked CO2 volumes.

 

Not that I can think of. It's going to reach those kind of temps and probably higher for bottle carbonating anyway. Lots of people cold crash and then bottle.

 

That's not really the case here. Headspace pressure is zero before, during, and after all the stages of brewing. If the Guardian is used as directed it will start collecting CO2 after high krausen, this is additional CO2 to be re-infused later. When the brew is finished at say 66 the beer will have a residual carbon dioxide level of 0.89 and that bladder will be all puffed up. Raise to 70 and residual will drop to 0.83 and the bag will be a little bigger. Drop temp to 40 and the bag will shrink considerably and I say given enough time residual CO2 will drop to 1.46 (plus you'll meet the German purity law).

This is what @riptorn is looking for, what residual to put into the calc to figure priming sugar. If he let's the brew rise to room temp, say 70, (without the Guardian) the residual will drop to 0.83 which is a big difference from the 1.46 . . . remember, headspace pressure is zero the entire time. The variables are temp and length of time for the little bubbles to move into/out-of the beer. My guess is when cold crashing it will be done in 48 hours and raising the temp will kick out the CO2 within a day but that's just intuition and am open for corrections from anyone with in depth knowledge.

The BF people have some pretty deep knowledge on brewing and I appreciate their admitting to the complexity of what's going on here. For example: A typical brew profile for me is ferm at 65 for 5 days, then slowly raise to 70 over the next 5 days, then ~half-day's rest at room temp (high 70s for me), then rack to keg and let sit overnight. If any new refermentation took place I'll vent out the purge valve, which will include the loss of any residual CO2 due to temp rise. Then drop the corny into keezer at 39. My co-brewer doesn't keg, so on bottling day will siphon out 2.5g to bottling bucket, temp is rising as the last bottle is capped in ~15 minutes . . . so what temp should be used for the priming calc?

Gas Laws rarely lie . . . given the right incentive a sharp Fluid Dynamicist could actually work the problem, but of course not practical for homebrewers like us. I take BF's advice and estimate where the beer was most stabilized (time/temp) and use that for the calc . . . results are good.

 

But @riptorn is not proposing using the Guardian as directed. He's proposing putting it on at/near the end of fermentation. Also, my explanation of the ~0.184 added volumes was in reply to you asking for the comps on the volumes resulting from 2 PSI from a CO2 cylinder (and not the Guardian). It's the right answer for that scenario.

 

If the Guardian is put on at high Krausen, the correct answer to how many "residual" volumes of CO2 there will eventually be at any given temperature is "nobody knows." Not without knowing how much total CO2 is actually being produced by the fermentation and also knowing details about the elasticity of the Guardian. The reason is that it won't really be "residual" the way we normally think about it. It will be a function of the starting amount of CO2 in that bag and how much headspace the bag contains when everything reaches equilibrium.

If I were going to use this device (and planned to carbonate with sugar), I would make sure to have a pressure gauge on the fermenter.

 

Sorry for the piecemeal replies. In the middle of a project and missing the edit window.

With the Guardian going on at high krausen, the CO2 volumes in the beer are going to be higher than 0.89 (or whatever "residual" is at your temp) at end of fermentation. All of that CO2 that was produced has been creating pressure. Unless the Guardian can easily expand to a near infinite volume, a lot of that CO2 (that would otherwise escape through an airlock) is going to stay in the (pressurized) beer. (Thus my comment about using a gauge on the fermenter to see what's really going on.)

 

Ah, hell. I didn't realize it had a relief valve. Yes, at the end of fermentation you'll have 0.5 gauge PSI pushing on the beer. If we knew the volume of the bag at the end, we could figure out the math, but it may not be worth it. At 0.5 PSI at 68F, you'd have a smidge over 0.03 extra volumes of CO2 in the beer.

 

And, I should have mentioned... even unlimited CO2 (which you don't have) being pushed at 0.5 PSI isn't going to change your carbonation noticeably. Again, sorry for the piecemeal.

 

This is true if the temp is constant. But lower the temp and and with unlimited CO2 expect it to follow the solubility table shown below (this is shown for one atmosphere):

The idea is to ignore pressuring the fermenter like a corny, the variable working here is temp. There is no attempt to force CO2 into the solution . . . rather change the solubility factor and have the solution allow the gas to enter. The headspace is at one atmosphere the entire time (actually 0.5psi with the Guardian which is almost the same as zero). But drop the temp and bubbles will flow into the water (beer). Raise the temp and watch it off-gas. You see the same thing when you boil water . . . after a period of time the dissolved oxygen is zero. But as it cools the air above will supply O2 back into the water. Given enough time, the DO will be same as pre-boil. All at one atmosphere of pressure. Time is the other variable involved.

I wouldn't trust a $19 (retail) gadget like this with a 0.5psi check valve (and they have two) any more than I could throw the ferm fridge over the house. While computing the quantity of CO2 needed for the temp swings and seeing if the bag is large enough is doable, it's probably not worth it. But the theory is correct.

For @riptorn , did you puff it up with your tank before attaching? Pretty sure you know the developers are just tinkering around with this and seeing what happens (it's on Version 3), and that's not necessarily bad (worked well for Orville & Wilbur). If you're really motivated they make lab grade carbon dioxide analyzers for liquids. It would tell the story . . .

 

I get that, but you don't have unlimited CO2. You have what's already in the beer and what's in the headspace/bag. That's it. The solubility table assumes you're open to the atmosphere, where the CO2 supply is essentially infinite, and continuously replaced.

Yes, basically. That is, until the total mass of CO2 available reaches equilibrium between the beer and the headspace, given the temperature, the beer volume and headspace volume.

ETA: If we knew the beer volume, the headspace volume, and the inflated bag volume at end of fermentation, we could compute the change in beer CO2 volumes due to crashing from 68F to 40F.