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Bunging the fermentation vessel to avoid oxidation during cold crashing

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Simonh82

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Wasn't sure whether to add this to the equipment forum or fermentation/yeast but I guess it's primarily about my equipment so hopefully that's OK.

After reading this article I've become concerned about the potential for oxygen pick up during cold crashing and wanted to get people's opinion's on a possible means to prevent it. I ferment in a 35L stainless steel fermentation vessel and at the end of fermentation I cold crash to drop the yeast/dry hops out of suspension.

Until recently, I've simply removed the top part of my airlock and covered it with sanitised foil, replacing the airlock when the temperature of the beer has stabilised. Because I'm often fairly busy, I regularly leave beers for a week or two at cold temperatures until I've got an evening free to keg. I now realise I've left them in contact with potentially a significant amount of oxygen for that time and I'd like to avoid this.

I can't remember where but I read recently about someone fermenting in kegs and simply sealing the keg when it came to cold crashing so that no oxygen could get in. Kegs are clearly not going to be troubled by the slight vacuum created inside. I wondered if you thought the type of SS fermenter I use would also be OK to do this with too. I don't want to go down this route if I end up with a fermentor with a caved in base for instance. It feels pretty robust. The lid is really solid and the walls and base are 0.6mm, which isn't super thick but doesn't feel flimsy. I guess that if I bunged the fermentor before cold crashing, the dissolved CO2 in solution would just be sucked out of the liquid to fill the vacuum in the head space, hopefully meaning that there wasn't a huge pressure created by the vacuum. I'd need to account for the reduction in CO2 this when kegging/bottling but I'm hoping that there wouldn't be any other issues.
 

Roland_deschain

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If your vessel will hold pressure, rig a bung with a gas port and hook it up to co2. If you kept it at even a 1/4 lb of positive pressure, there would be no worry of oxygen.
 
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Simonh82

Simonh82

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A bladder or bag of some sort will do the job without worry of draining an entire co2 tank should the fermenter not seal perfectly.View attachment 574807
I did think about using a bladder or balloon but I'm not sure there would be space in my fermentation chamber. I use an under counter fridge and the fermentor takes a significant amount of space. I might be able to squeeze something in the space above the fermentor.

If your vessel will hold pressure, rig a bung with a gas port and hook it up to co2. If you kept it at even a 1/4 lb of positive pressure, there would be no worry of oxygen.
It's not pressure rated, which I why I wanted to check if people thought that bunging it and letting a vacuum develop would damage it. Based on my rough calculations I think the pressure difference would be something like a drop of 0.46PSI. I hope that as the temperature fell slowly and the vacuum developed in the headspace, the CO2 would come out of solution and equalise that pressure. There should be about 0.8 volumes of CO2 in the beer at the end of fermentation, so there should be enough to compensate for the pressure difference.
 

eric19312

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I hope that as the temperature fell slowly and the vacuum developed in the headspace, the CO2 would come out of solution and equalise that pressure. There should be about 0.8 volumes of CO2 in the beer at the end of fermentation, so there should be enough to compensate for the pressure difference.
I'm trying this right now. I am dropping temp 5F at a time with a sealed spiedel fermentor. I do use a dual probe TC so I don't let fridge get lower than 5F below target. If I didn't have the dual probe TC I would just control the fridge based on fridge temp instead of beer temp during the cold crash. Idea being to keep the head space in the fermentor from getting too cold too fast. Give the beer time to gradually release CO2 from solution.
 
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Simonh82

Simonh82

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I'm trying this right now. I am dropping temp 5F at a time with a sealed spiedel fermentor. I do use a dual probe TC so I don't let fridge get lower than 5F below target. If I didn't have the dual probe TC I would just control the fridge based on fridge temp instead of beer temp during the cold crash. Idea being to keep the head space in the fermentor from getting too cold too fast. Give the beer time to gradually release CO2 from solution.
I'd be very interested to know how this turns out. Are you using a stainless steel Spiedel fermentor or one of the PET options?

I only ever control the air temperature in the fridge and usually chill in a couple of steps, so it probably takes 24 hours or more for the beer to reach cold crash temps. Hopefully this is long enough for the CO2 to come out of solution.
 
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Simonh82

Simonh82

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@eric19312 How did things work out when you bunged your fermentor? I'm about to start cold crashing and I'm trying to decide between bunging and seeing if I can attach some kind of co2 filled container.
 
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Simonh82

Simonh82

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@eric19312 How did things work out when you bunged your fermentor? I'm about to start cold crashing and I'm trying to decide between bunging and seeing if I can attach some kind of co2 filled container.
Sorry I didn't update this. I've been bunging the fermentor for a while now and it has been working well. Although the fermentor isn't pressure rated it doesn't seem to suffer from the vacuum created inside. The only issue is that to drain the fermentor into the keg I need to crack the seal and let in some air. I figure this is not a major issue as there is a blanket of CO2 sat on top of the beer but I have bought some foil party ballons with a view to fitting one during the cold crash. Not done it yet and bunging is certainly easier.
 
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