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Fermenting under pressure

Anybody with experience fermenting under pressure? I’m about to try my first attempt and was wondering about foaming / blow-off to plan for headspace in my fermentation vessels. I avoid foam control products, but I would imagine the pressure would keep foaming down somewhat. I’m using WLP925 lager yeast which recommends fermenting at 62-68 F and less than 15 psi.

I’ve never done this but I just did a fast review, especially the Brulosphy exbeeriment…sounds like you won’t have any headspace issues at all. Do you have a spunding valve, homemade or otherwise?

Well it seems even the big shooters don’t purposefully ferment under pressure… So what are you anticipating happening? Sneezles61

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I was just looking for someone who had done it for a bit of practical experience. … yes, I plan on regulating the pressure thru my spunding valves on 5 gal cony kegs. I usually ferment 10 gallon batches, so I will probably end up with close to 4.5 gal or more in a 5 gallon keg, which I think is a bit tight. I was hoping to avoid plumbing the whole apparatus thru an extra (overflow) keg if possible which is why I was looking for inputs. I’m thinking I am going to gunk up my valves otherwise.

Why go thru the trouble of fermenting under pressure? Just an experiment actually,… or maybe like the chicken, to see what is on the other side of the road? Actually, if I need an excuse, they are as follows:
1, Quicker fermentation of lagers.
2. Warmer fermentation of lagers.
3. Easier to harvest yeast for the next batch, especially with yeast strains that are a bit hard to come by.
4. More hygienic and fewer transfer of fluids, … sealed, always under pressure, admittedly, I’ll have to be fastidious about keeping trub out of the fermenter.
5. Natural carbonation… a bit subjective, yes… but some people (not me) can differentiate between forced carbonation and natural carbonation.
6. If I choose to bottle it is easier to bottle out of corny than a gravity/siphon arrangement like many people do.

I’ve read the Brewlosophy article. A good article, but I suggest he was another hop-head looking for a method to keep more hops in his beer, which is not really my motivation. Furthermore, while fermentation under pressure is not common in the USA, it is not unknown in Europe. And with large fermentation vessels, at .43psi gain per foot of wort, it doesn’t take long to achieve significant pressures in a fermenter open to the atmosphere. I would suggest fermenting under pressure is more common in this country than one might think.

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Good thinking… Have you checked the actual volume of your keg? I did ferment in the keg a while ago and it just wasn’t something for me. But, I did find there is more than 5 gallons of volume, it was just over 5.25 in my pin locks. I would agree about the amount of head pressure in those big, tall fermenters, and they typical utilize a blow off tube of sorts if you will… heck, maybe its a pipe. Would you think it was more prevalent many years ago as they tried to capture the CO2? Sneezle61

Thanks,it never occurred to me to check the actual volume of a 5 gal keg.

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Hi Max9, I hope this is not too late. I´ve been doing this in the past and, in my own opinion, I get a positive outcome all the way (except for a little more effort on keg cleaning, which in turn I saved avoiding do same in the fermenting bucket). I have a keg fermenting right now.

The article that best fit my understanding and I use to guide me out is the next link from Beersmith forum:

Also I agree in all your post above re reasons for. I like the fact I use just one keg I never open (or open once after fermentation) to dry hop (I use hop tea, the hops in a cup or 2 of water for 3 min then rest to warm until room temp then straight into keg with all the hop trub) I don’t mind too much for that dilution deviation though.
My parameters so far: I am doing fermentation with 1.5 to 2 BAR (roughly 30PSI) and between high 60´s and high 70´s (yet testing) I am trying to go as higher temp as possible because I live in tropical weather sort to save some energy and cold chamber space, and at day 3-4 I close the spun valve to achieve for instance 37-38 PSI (depends on actual temp and CO2 desired carbonation vols) then cold crash just to serving temperature. This batch I am aiming for 2.7Vol CO2, and final temp of 46 Deg. Is important to start the cold crashing when you achieve the rihgt pressure at actual temp, unless you have a CO2 cilinder or you can add little more sugar (also needs to be calculated the right ammount based on actual temp and pressure achieved) and refermet about 3 days more, which for me is the opposite I am looking for, I like the taste of almost green beer let’s say kellerbier style. SO I can cook on a weekend and have replenish for next one.

ps: I was not caring too much on notes latest batch and cannot find what I did in previuos ones, but I will be fermenting few batchs in a row under pressure and I will be more consistent gathering more data, also as I lost my mash calibration parameters and need to recalibrate my old cooler in beersmith2.

I will keep you guys posted.

You are replying to a two year old post and the OP has not posted since that day so it is unlikely he will respond. That said your info is interesting so please do keep us posted.

Thanks for the note hd4mark.
Yep I know. I came at this post as I was refreshing my research on the topic, and hopefully giving feedback on the topic will be of help for other random people like myself researching or for the sake of curiosity visiting here, a way to keep knowledge HB’s on a practical manner.


Our local brewer up here ferments under pressure and claims he can finish a huge volume up to 5 days earlier! I don’t think he was fermenting at as high a pressure as you are doing… With what you’ve got going here, I’d follow along… Sneezles61

There are stories on here about yeasts that cannot even handle the pressure of an airlock w/o stalling.

Hi and thanks for the reply. I’m curious, what yeast are you using? I used Whitelabs WLP925 and fermented around 15 psi. About the only problems I had was the availability of the yeast I was using. The local shop didn’t carry it, and as far as I know the only source is to mail-order it from Whitelabs. In the end, I bought a conical (which is more versatile and easier to clean than a corny) and moved on to other projects. ^…^

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