Why pressure fermenting in a Flex+ is a bad idea

[Donoroto]

Started the Q3 brew and left for 2 weeks. Put 4 gallons in the Spike Flex+ fermenter, and was not around to monitor it, although I followed the progress with my Tilt.

Came back to krausen marks all the way up, past the lid and well into the blowoff flask, which was filled with yeast.

If this had been a pressure fermentation, it could have exploded after the krausen clogged the spunding valve.

 

[Sunfire96]

View attachment 17125

Started the Q3 brew and left for 2 weeks. Put 4 gallons in the Spike Flex+ fermenter, and was not around to monitor it, although I followed the progress with my Tilt.

Came back to krausen marks all the way up, past the lid and well into the blowoff flask, which was filled with yeast.

If this had been a pressure fermentation, it could have exploded after the krausen clogged the spunding valve.

Isn't that a risk with any pressure fermentation using a spunding valve?

 

[Donoroto]

I suppose, but Spike told me it was a bad idea, and though I never tried it, I was doubtful because I never had the krausen rise above the 6 gallon mark.

Except this time.

 

[Minbari]

yup. you would need a secondary blow off chamber. something To contain The blow off material, Then Connect your Spunding Valve to.

Trucks use This Technique in keep water out of the Brake likes.

 

[HighVoltageMan!]

Keep in mind that fermenting under pressure suppresses the krausen. So it may or may not be an issue. I have never pressure ferment 1318, but that would be a good test. Most of the yeasts that do well with pressure fermenting are lager yeasts, which have less krausen.

Most top cropping yeast are pukers and probably shouldn’t be fermented under pressure because the main reason to do so is to reduce esters. Those yeasts are known for fruity easters, putting them under pressure would be counterproductive.

 

[Hawkbox]

Woof, glad nothing major happened Don.

 

[Donoroto]

I wish I'd been home to see it though...

I agree @Minbari , a secondary chamber with a big 1/2" tube connection to the fermenter, with maybe a gallon or two volume, should be OK.

This was K97, first time using it ever. And with only 4 gallons in there, overflow was the last thing on my mind.

 

[HighVoltageMan!]

K97 is a top cropper yeast, very high and active krausen. It’s a beast.

 

[GFHomebrew]

Holly Moses Don that's Crazy!

Yup i fermented it under 10psi it didn't fully attenuate only 72% I did drop it back to 5psi and upped the temp to 24c but gravity didn't budge from 1.010.
So I'm expecting the pressure caused the under attenuation.
Nothing wrong that I can tell with the beer mind you it did have a touch of Sulphur that's fadded.
The bottle I had the other night tasted good. I bottled two one for comp and one for comparrison to take on holiday.

Looking to brew Kolsch next with the saved slurry will probably let it ferment without any head pressure and see if I can get some more attenuation.

 

[Josh Hughes]

So @Trialben and @Donoroto i may need to lower my psi fermenting or open the valve?ill have about 2 gallons of headroom so I may be ok, don’t want the attenuation issue though. May use my corny lid with an air lock the first day or 2.

 

[BarbarianBrewer]

I think the key lesson here is to not seal a pressurized vessel and then leave town for two weeks!

 

[Donoroto]

I think the key lesson here is to not seal a pressurized vessel and then leave town for two weeks!

Bingo.
Spike told me that I should not try to pressure ferment in this thing, and I haven't, despite thinking I probably could. Now I see why I should not.

Anyone fermenting under pressure merely needs to consider what will happen if the krausen rises too high and clogs the spunding valve. If the answer is dangerous, rethink the plan, but if merely a big mess, you're good.

 

[Sunfire96]

Hypothetically, if pressure fermenting in a keg, the PRV would release around 40 PSI IIRC, even if the spunding valve is clogged? The pressure would most likely stall the yeast if in primary fermentation still, but I don't envision a corny-shrapnel scenario

 

[Donoroto]

Hypothetically, if pressure fermenting in a keg, the PRV would release around 40 PSI IIRC, even if the spunding valve is clogged? The pressure would most likely stall the yeast if in primary fermentation still, but I don't envision a corny-shrapnel scenario

I thought corny kegs prv were around 100, but a clogged prv might not open. I suspect no fermentation could reach the 130 psi max pressure for a corny keg though.

 

[Sunfire96]

I thought corny kegs prv were around 100, but a clogged prv might not open. I suspect no fermentation could reach the 130 psi max pressure for a corny keg though.

Ah, yep seems like "stock" PRVs are rated to max 100 PSI. I've also read some people pressure ferment in a keg without a spunding valve by using a "low pressure" PRV

https://www.soundhomebrew.com/corny-keg-relief-valve-10-12-psi/

 

[Minbari]

Ah, yep seems like "stock" PRVs are rated to max 100 PSI. I've also read some people pressure ferment in a keg without a spunding valve by using a "low pressure" PRV

https://www.soundhomebrew.com/corny-keg-relief-valve-10-12-psi/

makes sense. if one wanted to get very clever, you could alter a PRV with set screw, so you could vary the spring pressure. *poof* instant adjustable PRV.

 

[GFHomebrew]

Bingo.
Spike told me that I should not try to pressure ferment in this thing, and I haven't, despite thinking I probably could. Now I see why I should not.

Anyone fermenting under pressure merely needs to consider what will happen if the krausen rises too high and clogs the spunding valve. If the answer is dangerous, rethink the plan, but if merely a big mess, you're good.

The pressure reduces the krausen .
But once the pressure is released WATCH OUT !

 

[Over The Cliff Brewing]

I have been thinking about trying pressure fermentation. I brew mostly IPA's and the occasional brown or blonde ale. From some of the articles I have read, IPA's don't really benefit from pressure ferm. Any other opinions on this?

 

[Sunfire96]

I have been thinking about trying pressure fermentation. I brew mostly IPA's and the occasional brown or blonde ale. From some of the articles I have read, IPA's don't really benefit from pressure ferm. Any other opinions on this?

I'm interested in pressure fermentation for the CO2 capture. When the brew is almost done fermenting, set the spunding valve and let the beer carbonate itself. I don't think I'll be able to get a 5# CO2 tank, so I'll be able to save CO2 for carbing and serving this way

 

[HighVoltageMan!]

I have been thinking about trying pressure fermentation. I brew mostly IPA's and the occasional brown or blonde ale. From some of the articles I have read, IPA's don't really benefit from pressure ferm. Any other opinions on this?

Sunfire hit on it pretty good. IPA’s really don’t benefit from pressurize fermentation, but the spunding toward the end works really nice. You should first dry hop before spunding to avoid a hop volcano. The other benefit is closed transfers.