Author Topic: Cold crashing techniques to avoid suckback?  (Read 1022 times)

Offline Z-man

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Cold crashing techniques to avoid suckback?
« on: October 22, 2020, 02:23:01 PM »
Trying to avoid suckback during cold crashing and am exploring some ideas, but wanted to see what people think/have done. For reference, I have a plastic fermenter.

  • leave the S airlock on, filled properly with sanitizer, and hope it pulls in minimal oxygen
  • Remove the airlock and seal shut with sanitized tinfoil and a rubber band (sanitized) - do i risk collapsing the fermenter?
  • Fill a 1qt plastic bag with Co2 and run it into the bung so it only sucks in Co2

What have people done? Thanks all!

Offline ynotbrusum

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Re: Cold crashing techniques to avoid suckback?
« Reply #1 on: October 22, 2020, 03:30:20 PM »
If you have a large balloon (or similar capture bag) to attach as you approach the end of fermentation, you could let it fill and then use that CO2 blanket to fill the fermenter air space as the pressure drops with the temperature drop...
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Offline Richard

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Re: Cold crashing techniques to avoid suckback?
« Reply #2 on: October 22, 2020, 03:30:49 PM »
I have done all 3 of these. I started by doing nothing, just refilling the airlock as stuff got sucked in, but after a couple of lapses I decided that was too much trouble. Once I just sealed it shut, but I got a bit alarmed when I saw how much the sides of the fermenter buckled in. It is flexible material, but less flexible when cold and I worried that in the long term this could cause cracking.

Now I have a top with two holes: one for the airlock and one for a mylar balloon. The balloon hole is plugged with a small stopper until fermentation is chugging away and I feel that most of the head space has been purged with CO2. Then I pull out the stopper and add an empty mylar balloon that is attached to a shot bit of stainless tubing that fits tightly in the grommeted hole. The balloon fills with CO2 with plenty of capacity to cover the suckback during cold crash.
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Offline Z-man

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Re: Cold crashing techniques to avoid suckback?
« Reply #3 on: October 22, 2020, 04:20:56 PM »
Sounds like a balloon or airbag of some sort might be the best way. If you replace the airlock near the end of fermentation with a balloon or bag, it will just naturally fill up with Co2, then during cold crash suck that back in?

Any recommendations on the best kind of bag or balloon to use?Thanks!

Offline Z-man

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Re: Cold crashing techniques to avoid suckback?
« Reply #4 on: October 22, 2020, 04:25:03 PM »
Also, assuming you have to sanitize that balloon.....

Offline Richard

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Re: Cold crashing techniques to avoid suckback?
« Reply #5 on: October 22, 2020, 04:34:09 PM »
I first tried to replace the airlock with a balloon, but the timing turned out to be a bit tricky. Too early and the balloon fills up and blows itself off, too late and it doesn't fill up enough. That is why I decided to go with a balloon and an airlock in parallel. The CO2 fills the balloon, and when it is full the airlock begins to bubble again and keeps the pressure in the balloon from getting too high.
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Offline Z-man

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Re: Cold crashing techniques to avoid suckback?
« Reply #6 on: October 22, 2020, 04:42:14 PM »
Smart.  When you use both, doesn't the temperature drop still suck in the sanitizer from the airlock when crashing?
It's probably too late for me to do that this time around, since i am about 6 days in to fermentation and it will be ending soon-ish (it's an NEIPA with london ale iii - super aggressive)....I have my last dry hop tonight/tomorrow then will let it rest til i crash it.

i may just fill the balloon with Co2 from my 5lb tank and place it on there right before crashing instead.

Offline BrewBama

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Re: Cold crashing techniques to avoid suckback?
« Reply #7 on: October 22, 2020, 04:52:04 PM »
I transfer to a keg and apply CO2 pressure to cold crash.
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Offline Z-man

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Re: Cold crashing techniques to avoid suckback?
« Reply #8 on: October 22, 2020, 05:39:02 PM »
Do you get super yeasty pulls from the keg with that? I've read diff opinions on that method...

Offline BrewBama

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Cold crashing techniques to avoid suckback?
« Reply #9 on: October 22, 2020, 07:43:18 PM »
Do you get super yeasty pulls from the keg with that? I've read diff opinions on that method...
No. I use a floating dip tube and often fine. Crystal clear beer after the first cloudy pint.


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« Last Edit: October 22, 2020, 07:53:02 PM by BrewBama »
“From man’s sweat and God’s love, beer came into the world.” — St. Arnold

Brewed in the Tennessee Valley. Rocket City — Huntsville AL

Offline Richard

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Re: Cold crashing techniques to avoid suckback?
« Reply #10 on: October 22, 2020, 07:51:05 PM »
Smart.  When you use both, doesn't the temperature drop still suck in the sanitizer from the airlock when crashing?
It's probably too late for me to do that this time around, since i am about 6 days in to fermentation and it will be ending soon-ish (it's an NEIPA with london ale iii - super aggressive)....I have my last dry hop tonight/tomorrow then will let it rest til i crash it.

i may just fill the balloon with Co2 from my 5lb tank and place it on there right before crashing instead.
There is no drop in pressure unless the balloon is completely emptied, which never happens for me. Until then the balloon can crumple down and shrink its volume to keep the pressure constant during the cold crash. Filling a balloon from a tank and putting it in place of the airlock will also work. Now that I have the parts I find it very easy to put the balloon in place during active fermentation and then be done with it.
« Last Edit: October 22, 2020, 11:01:52 PM by Richard »
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Offline ynotbrusum

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Re: Cold crashing techniques to avoid suckback?
« Reply #11 on: October 22, 2020, 08:22:30 PM »
Do you get super yeasty pulls from the keg with that? I've read diff opinions on that method...
No. I use a floating dip tube and often fine. Crystal clear beer after the first cloudy pint.


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This is what I do, but not fining (whirlfloc and Brew Tan B, though).
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Offline scrap iron

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Re: Cold crashing techniques to avoid suckback?
« Reply #12 on: October 23, 2020, 11:51:03 AM »
I tried using a long blow-off tube in a loop, worked ok but still some suck back. Then tried the balloon method and couldn't get the timing right. I finally bought the Jaybird co2 harvester after making a homemade one out of drilled stoppers and canning jar lids. The homemade worked but was hard to drill the lids and they started to show some rust after sanitizing. They are pricey but I got mine as a gift.
https://www.norcalbrewingsolutions.com/store/CO2-Carbon-Dioxide-Harvester-Kit.html
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Offline kramerog

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Re: Cold crashing techniques to avoid suckback?
« Reply #13 on: October 23, 2020, 02:02:44 PM »
I have done all 3 of these. I started by doing nothing, just refilling the airlock as stuff got sucked in, but after a couple of lapses I decided that was too much trouble. Once I just sealed it shut, but I got a bit alarmed when I saw how much the sides of the fermenter buckled in. It is flexible material, but less flexible when cold and I worried that in the long term this could cause cracking.

Now I have a top with two holes: one for the airlock and one for a mylar balloon. The balloon hole is plugged with a small stopper until fermentation is chugging away and I feel that most of the head space has been purged with CO2. Then I pull out the stopper and add an empty mylar balloon that is attached to a shot bit of stainless tubing that fits tightly in the grommeted hole. The balloon fills with CO2 with plenty of capacity to cover the suckback during cold crash.
I'm going to have to try this since I have the "bungs" that go over the top of the carboy and have two prongs with outlets on top.

Offline Z-man

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Re: Cold crashing techniques to avoid suckback?
« Reply #14 on: October 23, 2020, 03:28:02 PM »
I'm just adding the mylar balloon to a tube and attaching to the bung right before crashing. I have the whole apparatus set up and ready to go, so the swap out time should only be a matter of seconds (to reduce oxidation). I also have the floating dip tube for the keg, works great.

Seems like the best method, with the least fuss, is to harvest Co2 from the beginning combined with an airlock of some sort. going to try to build one of these sometime in the future:

https://varikonniemi.wordpress.com/2018/07/26/co2-harvesting-airlock/

i like this idea because there are no tubes to mess with, unless you need to attach the blow off to the airlock, which is pretty easy to do.