Cold crash suck back from blowoff tube

[USMChueston0311]

I’d even kick the idea around of using an Un-drilled stopper bung and putting .5-1 lb of co2 in carboy and quickly plugging it closed with bung. I would try in plastic carboys before glass. I don’t see why this would hurt. You have put positive pressure in place. Just a though and something to experiment with.

 

[li walker]

Cheers!

 

[Bobby_M]

To be honest, I'm sure that there may be some potential risk from O2 entering during the cold crash. It does make sense but its unclear to me how much this actually influences the finished product. I cold crash often and like @USMChueston0311 , I don't believe any of my beers have had problems from it.

The idea of near zero O2 exposure during a cold crash sounds good but I maintain my initial response; I don't feel its worth the hassle. I think I'll stick to the K.I.S.S. principle for the time being..

Back to the OP, those jar solutions seem great for eliminating suck-back. They probably do a lot to minimize the related O2 infiltration too since they would be full of CO2 post fermentation and it would take a lot of suck-back to pull O2 in from the jars, up the tubes, into the fermentor and into your beer.

If I needed a blow-off tube and didn't want to remove it for a cold crash, I'd set myself up with the jars...

Try it with a NEIPA and report back.

 

[Nagorg]

Try it with a NEIPA and report back.

Thanks but I'll pass on the NEIPA... I kinda think those are flawed beers in the first place so adding another flaw....?

 

[day_trippr]

^boooo!^

 

[Bobby_M]

Thanks but I'll pass on the NEIPA... I kinda think those are flawed beers in the first place so adding another flaw....?

You dont have to like them. The point is that it is a style that most amplifies oxidation problems. Most people who attempt the style have oxygen damage and cold crashing is one way to do it wrong.

 

[doug293cz]

In another thread, someone did the math and determined that even with 1.5 gal. headspace and including the space in the jars, the suckback from chilling from 60s to just above freezing would only involve less than 1 qt. of contraction. If you get one of those "CO2 Harvester" units, use 1/2 gal jars and about a quart of Starsan in them. There won't be any air getting back into your fermenter.

Yes, if you just consider gas "contraction" due to cooling, the suck back volume when going from 68°F (20°C, 293.15°K) to 32°F (0°C, 273.15°K) is:

Headspace Volume * (293.15 - 273.15) / (293.15) = Headspace Volume * 20 / 293.15
= Headspace Volume * 0.0682
​

So, for headspace volume = 1.5 gal (6 qts) the suck back would be:

6 qts * 0.0682 = 0.41 qt
​

What all this misses however, is that as the temp is lowered, CO2 from the headspace will be absorbed into the beer. I did a complete analysis of the reabsorption here. The net is that when cold crashing to about 32°F, about 46% of the CO2 in the headspace absorbs into the beer (if cold crashed long enough to reach equilibrium), for an additional suck back of 0.46 * 1.5 gal = 0.69 gal or 2.76 qts. The total suck back during a long cold crash is about 2.76 + 0.41 = 3.2 qts. The good news is that you would have to cold crash about 3 weeks, or more, to reach equilibrium.

Using a simple exponential rate model for CO2 absorption, I come up with the following estimates of CO2 reabsorption vs. cold crash time:

​

You must add the 0.4 qts of gas cooling shrinkage to the right column to get the total suck back.

Brew on

 

[MaxStout]

Interesting. I didn't even consider CO2 reabsorption, but the math makes sense. The takeaway is that cold-crashing for a short period won't be enough time for a large qty. of CO2 to reabsorb (with subsequent air intake to replace the volume). Cold-crashing a few days (e.g., to get the yeast to floc) would be such an instance.

However, this could be a problem for lagering.

 

[Dland]

If wort is mostly cooled before gets into fermentor, and it is kegged before it is crashed, never had a problem.

Though I have to admit some people have come up with some nice work arounds in this thread, if it is a problem for them.

 

[mscroggi]

In another thread, someone did the math and determined that even with 1.5 gal. headspace and including the space in the jars, the suckback from chilling from 60s to just above freezing would only involve less than 1 qt. of contraction. If you get one of those "CO2 Harvester" units, use 1/2 gal jars and about a quart of Starsan in them. There won't be any air getting back into your fermenter.

Yeah I agree it isn't as much as you would think. I just did a cold crash with the Mylar balloon. It only deflated maybe halfway. Not really that much.. I wasn't even close to sucking star-san up into the fermenter.

 

[MaxStout]

There's a thread around here where they addressed this for users of the CO2 harvester with 1/2 gallon jars. It was suggested that you fill the first jar almost full with water (or Starsan). Outgoing CO2 will push this liquid to the 2nd jar. Due to the amount of outgoing CO2 volume, the air will be displaced such that the atmosphere in the headspace has only a few ppb O2. When cold-crashing, you now have 1/2 gallon of CO2 to be drawn in before O2 is sucked from the second to the first jar (and into the fermenter). Given the contraction volume plus the CO2 absorption into the beer, you'd have at least a few days of cold-crashing before O2 makes its way in.

 

[doug293cz]

There's a thread around here where they addressed this for users of the CO2 harvester with 1/2 gallon jars. It was suggested that you fill the first jar almost full with water (or Starsan). Outgoing CO2 will push this liquid to the 2nd jar. Due to the amount of outgoing CO2 volume, the air will be displaced such that the atmosphere in the headspace has only a few ppb O2. When cold-crashing, you now have 1/2 gallon of CO2 to be drawn in before O2 is sucked from the second to the first jar (and into the fermenter). Given the contraction volume plus the CO2 absorption into the beer, you'd have at least a few days of cold-crashing before O2 makes its way in.

That sounds really familiar. doug293cz's epic post on CO2 generation
https://www.homebrewtalk.com/forum/...voir-for-your-fermenters.632181/#post-8061426

Brew on

 

[MaxStout]

That's it!

 

[day_trippr]

"Another case cracked!"

 

[Vintage Iron]

In another thread, someone did the math and determined that even with 1.5 gal. headspace and including the space in the jars, the suckback from chilling from 60s to just above freezing would only involve less than 1 qt. of contraction. If you get one of those "CO2 Harvester" units, use 1/2 gal jars and about a quart of Starsan in them. There won't be any air getting back into your fermenter.

So if this is the case, and CO2 will always fall (and oxygen will always rise) does it really matter how much air gets in during cold crashing because the blanket of CO2 will always be in contact with the top of the beer in the fermenter. Right?? (Scratches head)

 

[day_trippr]

The whole "CO2 blanket" thing is a total myth...

 

[doug293cz]

So if this is the case, and CO2 will always fall (and oxygen will always rise) does it really matter how much air gets in during cold crashing because the blanket of CO2 will always be in contact with the top of the beer in the fermenter. Right?? (Scratches head)

CO2 does NOT fall, and O2 does not rise. Watch the following video. CO2 has just about the same molecular wt as the NO2 later in the video. The CO2 "blanket" is a myth.

GCSE Science Revision - Diffusion of Gases - YouTube

Brew on

 

[MaxStout]

If CO2 and O2 are together in a vessel, they will mix, despite their different densities. Just as air is comprised of different gases mixed together. The only time CO2 produces an effective "blanket" is when it is pure CO2.

 

[Vintage Iron]

Makes sense. Thanks for setting me straight. I'm still learning about this hobby everyday from you guy!

 

[Nagorg]

FWIW, all this O2 talk has made me opt for skipping the cold crash on the beer currently in my conical! I cant say that I've really noticed a benefit from doing it in the first place, I've mainly done it because I can. It will be cold crashed soon enough when its kegged and placed in my keezer for carbing...

I may consider the jars or something along that line for my next lager though... Or maybe I'll try spunding instead!

 

[mscroggi]

FWIW, all this O2 talk has made me opt for skipping the cold crash on the beer currently in my conical! I cant say that I've really noticed a benefit from doing it in the first place, I've mainly done it because I can. It will be cold crashed soon enough when its kegged and placed in my keezer for carbing...

I may consider the jars or something along that line for my next lager though... Or maybe I'll try spunding instead!

I built out a spunding valve not too long ago.. and I really liked it.. The last batch I brewed, I was going to go the spunding valve route.. but I messed around too long and the fermentation finished.. hahaa .. I have to say it doesn't get any simpler and the results were really good. The beer wasn't as clear as it would have been after a cold crash for a couple of days before transferring.. but I am not hung up on getting the clearest beer possible..

 

[cactusgarrett]

For what it's worth, I've done something similar yet less complex and expensive to combat the cold crash issue. Few bucks for the fittings and balloons. Allows for a quick changeout of balloons when needed.