Weird and probably stupid cold crash question

[toddo97]

I know the big problem with cold crashing is suck back. If I were to use a solid bung rather than an airlock when I cold crash it would presumably prevent any suck back. Once it's reached 32-34 degrees for a day or two, would it make any sense to bring the temp back up to fermentation temps? Would that balance out the pressure difference caused by the crashing but still retain the settling benefits?

 

[Rob2010SS]

You fermenting in a plastic container or a glass carboy or other?

I get worried with the carboy because it's not meant to hold pressure, but I'm not smart enough to know whether that would cause enough pressure inside the carboy to cause an issue.

If you're using a plastic container, you could. It will definitely deform the container though.

Personally, I'd just use the "S" type airlock. Try to fill it with most of the liquid on the one side and as the beer cold crashes, it'll pull the liquid to the other side. This is how I do all my crashes now.

In regards to your question, if you brought it back up to fermentation temps, it wouldn't hurt the effects of your cold crash. As soon as you move the fermenter though, that usually stirs some stuff up.

In regards to the pressures, someone smarter than me will have to comment on that.

 

[GPP33]

It'll mostly come back to the same pressure but there will be more CO2 in solution so you'll still have a bit of a vacuum which means air will suck in when (even if) you can get the bung out. I'm not aware of any fermenter that is designed to hold a negative pressure. There are ways to ensure the suck back takes only CO2, I would figure out how to implement one of them before cold crashing. I would strongly consider asking yourself if cold crashing is worth the risk of oxidation. I cold crash only when I have more than a few ounces of dry hop and that's only to help with leaving the plant matter behind when I transfer. I do not notice a difference in clarity of the finished product but in all fairness the ones I do crash are dry hopped which naturally leaves some haze, though they eventually drop completely clear as do all of the ones that don't get cold crashed.

IMHO home brewers do more damage by cold crashing than not (no actual data to back that up, just an opinion). If you can't feed it CO2 during the crash you need to do away with it as we are doing away with secondary for the same exact reasons. It'll cold crash in the bottle/keg when you refrigerate it.

 

[GPP33]

And there are no stupid questions in this hobby. Just realize that most of what you get in response will come from very limited experience, non scientific observations and old wives tales about how things must be done. Question everything!

 

[seatazzz]

When I cold crash, I do it gradually (yes I have a fermentation fridge and a temp controller). That way I mitigate the suckback. Even so, I will usually sanitize some aluminum foil and wrap that over the top of the carboy (or the hole in the fermenter lid if I'm going that way). Once the temperature is where I want it I'll replace the airlock. Have not had one problem with oxidation. My thinking is, as long as you aren't agitating the fermenter, the co2 layer should stay intact and prevent oxidation (or nasties getting through).

 

[GPP33]

When I cold crash, I do it gradually (yes I have a fermentation fridge and a temp controller). That way I mitigate the suckback. Even so, I will usually sanitize some aluminum foil and wrap that over the top of the carboy (or the hole in the fermenter lid if I'm going that way). Once the temperature is where I want it I'll replace the airlock. Have not had one problem with oxidation. My thinking is, as long as you aren't agitating the fermenter, the co2 layer should stay intact and prevent oxidation (or nasties getting through).

Interesting theory but suck back caused by gasses taking up less volume at lower temperatures and gas absorption is a function of lowest temp reached, not the rate at which you get there.

Regarding the CO2 blanket, it’ll break down as molicules bounce around and mix. Given enough time the gas in the head space will be a homogeneous mixture. How much time is enough time is debatable but 24 hours is almost certainly enough.

 

[toddo97]

I have an SS Brewbucket so I'm not so worried about the pressure build up (vacuum build up?), but maybe I'll try and see how it goes. I suppose I could try gelatin for clarity, but I wonder how much more difficult yeast harvesting will be with all of that additional gunk that comes along with gelatin.

 

[GPP33]

This reminded me of this video. Note reason #4 for negative pressure. I highly doubt you’ll see this much vacuum but I also doubt SS Brew Tech will rate that bucket for a vacuum (my guess is it'll work if you can seal off the hole in the lid). For every 1 psi of pressure drop there will be 122lbs of pressure on the lid and the bottom, I’ve heard you can expect 2psi from cold crashing but I’m not sure if that’s at all accurate.

 

[eltorrente]

I wouldn't worry about it. I just make sure I have Starsan in my airlock, and don't worry about the suckback.

The CO2 isn't getting displaced by air coming in, plus CO2 is heavier than air, so the oxygen isn't going to dive right into your beer. You'll still have a blanket of CO2 in the fermenter.

 

[specharka]

I wouldn't worry about it. I just make sure I have Starsan in my airlock, and don't worry about the suckback.

The CO2 isn't getting displaced by air coming in, plus CO2 is heavier than air, so the oxygen isn't going to dive right into your beer. You'll still have a blanket of CO2 in the fermenter.

Oh good god, not this again. This myth needs to die.

There’s no such thing as a CO2 “blanket”, all gases disperse in time to the boundaries of their container, and do it much quicker than you would expect. Seconds of exposure is all your beer needs to become oxidized. And if you ferment in plastic, oxygen will permeate the fermenter walls, so even if your fermentation process is a closed environment, your beer is still not safe from oxidation.

 

[GPP33]

I wouldn't worry about it. I just make sure I have Starsan in my airlock, and don't worry about the suckback.

The CO2 isn't getting displaced by air coming in, plus CO2 is heavier than air, so the oxygen isn't going to dive right into your beer. You'll still have a blanket of CO2 in the fermenter.

It's great that you have a process that works for you but so the facts are straight, all of the CO2 isn't getting replaced by air but the vacuum created is certainly getting back filled with air, and a significant amount of air to boot. People on HBT have documented needing to add multiple balloons of CO2 to keep the pressure equalized. Also, while CO2 is heavier than air the gases mix. Ever smell perfume or your buddies fart from across the room? That's because molecules bounce around and mix. The air and CO2 bounce around and become a homogeneous mixture in pretty short order. The CO2 blanket is a very short lived phenomena. As I have said multiple times here, I have no idea why someone would cold crash a beer if they can't keep the container filled with only CO2 or another inert gas. We go to great extents to develop recipes, sanitize, pitch the exact amount of yeast, keep temps in check, then just open the door and let air and everything it carries in. No thanks, not in my beer.

 

[ApolloSimcoe]

or your buddies fart from across the room

unfortunately, yes i have.

I cold crash for certain beers and only in certain situations. Not sure if its best practice but in the past i have clamped the blow-off tube and dropped the temps over a 2-3 day period...no suck back however it is possible that the clamp, the bung etc are not 100% sealed and i am pulling in O2.

Also if you are using the brewbucket you should be able to cold crash easily. Can you connect CO2 to the hose barb? I have heard that people will slowly bubble CO2 through the hose barb. Once you see bubbles coming through the airlock replace it with a solid bung, CO2 off, then crash it. Never tried, just what i have heard has been done.

 

[specharka]

unfortunately, yes i have.

I cold crash for certain beers and only in certain situations. Not sure if its best practice but in the past i have clamped the blow-off tube and dropped the temps over a 2-3 day period...no suck back however it is possible that the clamp, the bung etc are not 100% sealed and i am pulling in O2.

Also if you are using the brewbucket you should be able to cold crash easily. Can you connect CO2 to the hose barb? I have heard that people will slowly bubble CO2 through the hose barb. Once you see bubbles coming through the airlock replace it with a solid bung, CO2 off, then crash it. Never tried, just what i have heard has been done.

It’s theoretically impossible to maintain a perfect seal if your beer has finished fermentation and your FV reaches equilibrium conditions. The volume of gas has to be made up from ambient air. Where else would it come from?

Here’s a few ways to cold crash without oxidizing your beer:
1) Ferment in a keg and use a spunding valve to build up pressure for the last 1.5-2P of fermentation. 99% effective.
2) Pipe in CO2 through a silicone bung and monitor pressure via a balloon, blowoff hose, or the like. I’ve found glass carboys are structurally safe to at least 2-3 psig (but I wouldn’t risk going much higher than that...there’s a lot of energy in that volume). Use a couple hose clamps and you can really minimize any leakage. Probably 90-95% effective since you still have to adjust the airlock.
3) Craft a double airlock with mason jars and use the CO2 evolved during fermentation to replace volume during a cold crash. Efficacy based on seal design and airlock size. Nifty and efficient, but not recommended.

 

[Murphys_Law]

It’s theoretically impossible to maintain a perfect seal if your beer has finished fermentation and your FV reaches equilibrium conditions. The volume of gas has to be made up from ambient air. Where else would it come from?

Here’s a few ways to cold crash without oxidizing your beer:
1) Ferment in a keg and use a spunding valve to build up pressure for the last 1.5-2P of fermentation. 99% effective.
2) Pipe in CO2 through a silicone bung and monitor pressure via a balloon, blowoff hose, or the like. I’ve found glass carboys are structurally safe to at least 2-3 psig (but I wouldn’t risk going much higher than that...there’s a lot of energy in that volume). Use a couple hose clamps and you can really minimize any leakage. Probably 90-95% effective since you still have to adjust the airlock.
3) Craft a double airlock with mason jars and use the CO2 evolved during fermentation to replace volume during a cold crash. Efficacy based on seal design and airlock size. Nifty and efficient, but not recommended.

Curious why you wouldn’t recommend the “double airlock”?

 

[specharka]

Curious why you wouldn’t recommend the “double airlock”?

Just because it requires perfect seals between each of the airlocks, which is remarkably difficult to achieve. The grommets on plastic fermenters are engineered and they are still leaky af.

Hose clamps and silicone bungs are a little bit more reliable, in my experience.

 

[GPP33]

It’s theoretically impossible to maintain a perfect seal if your beer has finished fermentation and your FV reaches equilibrium conditions. The volume of gas has to be made up from ambient air. Where else would it come from?

Here’s a few ways to cold crash without oxidizing your beer:
1) Ferment in a keg and use a spunding valve to build up pressure for the last 1.5-2P of fermentation. 99% effective.
2) Pipe in CO2 through a silicone bung and monitor pressure via a balloon, blowoff hose, or the like. I’ve found glass carboys are structurally safe to at least 2-3 psig (but I wouldn’t risk going much higher than that...there’s a lot of energy in that volume). Use a couple hose clamps and you can really minimize any leakage. Probably 90-95% effective since you still have to adjust the airlock.
3) Craft a double airlock with mason jars and use the CO2 evolved during fermentation to replace volume during a cold crash. Efficacy based on seal design and airlock size. Nifty and efficient, but not recommended.

I would add the balloon trick as I think it's a nifty and effective solution. I haven't done it myself but it seems to work well, it's easy and cheap to set up and there's no risk to life or limb if something goes wrong.

 

[Bobby_M]

 

[Bobby_M]

You fermenting in a plastic container or a glass carboy or other?

I get worried with the carboy because it's not meant to hold pressure, but I'm not smart enough to know whether that would cause enough pressure inside the carboy to cause an issue.

If you're using a plastic container, you could. It will definitely deform the container though.

Personally, I'd just use the "S" type airlock. Try to fill it with most of the liquid on the one side and as the beer cold crashes, it'll pull the liquid to the other side. This is how I do all my crashes now.

In regards to your question, if you brought it back up to fermentation temps, it wouldn't hurt the effects of your cold crash. As soon as you move the fermenter though, that usually stirs some stuff up.

In regards to the pressures, someone smarter than me will have to comment on that.

Oxygen will definitely be pulled into the fermenter. It wants about 1.5 liters of makeup volume.

 

[GPP33]

I love the creativity of brewers!

 

[MaxStout]

If you have 50 bucks, get one of these.

 

[toddo97]

Any other thoughts on my idea about raising temps after cold crashing to hopefully lessen suckback vacuum?

 

[day_trippr]

Any other thoughts on my idea about raising temps after cold crashing to hopefully lessen suckback vacuum?

A bit pointless, imo. The suckback would not change - it's defined by the coldest temperature reached - and the damage is already done...

Cheers!

 

[Bobby_M]

Any other thoughts on my idea about raising temps after cold crashing to hopefully lessen suckback vacuum?

Raising the temp will cause some particles to rise back up to the surface as co2 comes out of solution. If you are kegging, youd be wasting energy to go back down again.

 

[Blazinlow86]

Fwiw prior to switching to a unitank I did at least 50 double batches in glass carboys. Crash cooled everytime with a soft rubber stopper. Never had a broken carboy or even a sucked in stopper. When removing the stopper there was the slightest amount of suckback however I always removed it immediately when switching to the carboy cap then pressure transferring to the kegs. I tried a diy 2 jar setup another user poster but I couldn't get a good seal. Also tried using the balloon method but wasn't a fan of having to try to zap strap it to keep from leaking. After seeing how much easier it was to clean the unitank I sold my 8 glass carboys and bought 2 fermonsters for a backup system and added solid lids with ball lock gas connectors to avoid all that. Cheers

edit sorry i just noticed you are using brew buckets not glass carboys. i have no first hand experience but would imagine you may crush a brew bucket using my old method. i would think its pretty easy to get a ball lock gas post and mount it on the lid/ plug the airlock stopper and use low pressure like 1 -2 psi

 

[jiMithing83]

Oh good god, not this again. This myth needs to die.

There’s no such thing as a CO2 “blanket”, all gases disperse in time to the boundaries of their container, and do it much quicker than you would expect. Seconds of exposure is all your beer needs to become oxidized. And if you ferment in plastic, oxygen will permeate the fermenter walls, so even if your fermentation process is a closed environment, your beer is still not safe from oxidation.

Really? Because gases can and do separate. H2S, for instance, will settle close to the ground even outside, and is only ~5 g/mol more dense than air. You can also have co2 buildup in low lying areas (https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxide.html).

Whether or not this happens at the homebrew scale and with the turbulence levels cold crashing would cause, I can't say. But co2 blankets absolutely are a real thing. Ask anyone who works at a refinery or chemical plant, many use nitrogen blankets but some use co2.

/ nerdrant

 

[GPP33]

Really? Because gases can and do separate. H2S, for instance, will settle close to the ground even outside, and is only ~5 g/mol more dense than air. You can also have co2 buildup in low lying areas (https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxide.html).

Whether or not this happens at the homebrew scale and with the turbulence levels cold crashing would cause, I can't say. But co2 blankets absolutely are a real thing. Ask anyone who works at a refinery or chemical plant, many use nitrogen blankets but some use co2.

/ nerdrant

CO2 will certainly form an area of higher concentration in low lying areas UNTIL it diffuses. CO2 released from a tank is cold, so you have a denser (cooler) and heavier gas which will naturally sink and form a blanket. However, as soon as you stop the supply of CO2 it will rather quickly diffuse into the air. Remember that people will suffocate at slightly lower oxygen levels, so what OSHA is referring to isn’t necessarily a 100% CO2 blanket but an area with slightly lower O2 levels. Yes, you’ll have higher levels of CO2 down by the surface of the beer, no it won’t be oxygen free. Is it enough to ruin your beer? Why take a chance when it’s so easy to avoid. That’s my 2 cents.

 

[specharka]

Really? Because gases can and do separate. H2S, for instance, will settle close to the ground even outside, and is only ~5 g/mol more dense than air. You can also have co2 buildup in low lying areas (https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxide.html).

Whether or not this happens at the homebrew scale and with the turbulence levels cold crashing would cause, I can't say. But co2 blankets absolutely are a real thing. Ask anyone who works at a refinery or chemical plant, many use nitrogen blankets but some use co2.

/ nerdrant

That’s a bit of an obscure non-sequitur.

I’m not really interested in debating introductory physical chemistry. Point is that the “CO2 blanket” idea in the homebrewing realm effectively contributes to oxidized beer and deserves to be debunked to prevent novice homebrewers from falling into unnecessary pitfalls.

 

[AZCoolerBrewer]

And there are no stupid questions in this hobby. Just realize that most of what you get in response will come from very limited experience, non scientific observations and old wives tales about how things must be done. Question everything!

I think it’s interesting what you say, but I would even take it one step farther and say that few have experience, really only those who didn’t listen to anyone at all and had to learn the hard way through trial and error with no human input. Most just take the group think and it works so why screw up a batch of beer to see what doesn’t work.

Old wives tales are the only data that homebrewers have besides unhappy accidents and Brülosophy.

As far as science? No science has been done in my kitchen, maybe experiments, maybe direct observation, but no science. My favorite is when an actual scientist claims that you should brew one way or another based on the science they do, but those guys really aught to know better that in science only very controlled and categorized results can be compared apples to apples or the comparison is completely in question. I might use tools that scientists use that can give me pertinent information to help me, but doing science in and of itself? Probably not. Science has helped us at the yeast factories, hop farms and barley farms/maltster, but we don’t do any real science on the homebrew level.

The three pillars of good brewing are:

Do what works for other people.

Use quality ingredients.

Keep everything clean and sanitized

 

[doug293cz]

I've lost track of how many times I have posted this video (and others have posted before me), but the CO2 blanket myth lives on.



Note that Br2 has a molecular weight of 159.8. Air has an average molecular wt of about 28.8. CO2 has a molecular weight of 44. Br2 has a density 159.8 / 44 = 3.6 times higher than CO2, and the Br2 completely homogenizes with are in the video in about 15 minutes, without aid of air currents or convection. Later in the video the NO2 (molecular wt 46, slightly higher than CO2) homogenizes very much faster than Br2.

Just opening a closed vessel will create air currents that will greatly speed up the mixing compared to diffusion alone.

Brew on

 

[AZCoolerBrewer]

I’m just not sure that oxygen exposure is as big a deal as everyone makes it out to be. Even in the case of the purple NEIPA, how can we know that it is from oxygen and not some other chemical reaction. Maybe the myrcinol reacts with the beta glucodines to unisomerize the 2 diasinine?