Headspace in fermenter under pressure

[Alf34]

Hello

I have been thinking about purchasing the fermenter King Junior 10 liters PET Pressure Fermenter from Keg King. I always brew small batches, around 4-5 liters in the fermenter. I plan to ferment under pressure my next hoppy beers. I was wondering if this fermenter would suit my needs since in this case I would have a lot of headspace in the fermenter, being only half filled in the end. I am not sure if that could cause some oxidation problems or it would not be a problem, since it's fermented under pressure anyway and the C02 produced by fermentation fills that headspace regardless of how big it is.

My plan is to wait under dry hopping and then put It under pressure to capture all those volatile aromas, but I need to make sure this fermenter is a good option for me.

Thanks!

 

[doug293cz]

If your fermenter remains sealed during the entire fermentation, then you will not have oxygen exposure issues. The ratio of wort/beer volume to headspace volume will be similar to the situation of purging a 5 gal corny keg with a 5 gal batch of fermenting beer, so this analysis will be close.

However, opening the fermenter (which will allow more O2 into the headspace) complicates things. Most of the CO2 is generated during the early, most active, stage of fermentation, and CO2 generation slows way down near the end of fermentation. Since dry-hopping is often done near the end of fermentation, there will probably not be enough CO2 to do a complete headspace purge if you have to open the fermenter to add the dry hops. This is why brewers really serious about O2 exposure minimization use CO2 purged hop bongs for dry hopping.

Brew on

 

[Alf34]

But I could always open the fermenter, quickly add the dry hops, close it, and then apply CO2 and purge a few times right?

 

[doug293cz]

But I could always open the fermenter, quickly add the dry hops, close it, and then apply CO2 and purge a few times right?

That would help, but there is no way to know how much O2 you let in (unless you own a very sensitive, very expensive O2 meter), and therefore no way to know how much purging is needed to get it back down to acceptable levels. A pressurize and purge cycle at 15 psi gets rid of 1/2 of the O2 in the headspace, and a cycle at 30 psi gets rid of 2/3 of the existing O2. Trick is to get your total packaged oxygen (TPO) down below 100 parts per BILLION. So, if you have 5 liters (~5 kg) of beer, your O2 content (headspace + beer) needs to be below about 500 micrograms.

Brew on

 

[Willy]

@doug293cz - the analysis link above made me sit down, realizing I was overwhelmed by the breakdown of gases, pressures, etc. whoa. Very nice, and happy to be in awe. Wow.

So ... A question for this thread... If I am fermenting with a 10 gallon torpedo corny with a modified lid (w 1 1/2" TC)...
The corny is about 31" high.

I plan to ferment a lager at about 55°F, using a blowoff into starsan for the first few days, then a prv set to about 10-12 psi...
What volume of beer is okay for the fermenter batch size. My guess is 7.5-8 gallons but just a guess. I've fermented a 4.75 g batch in a 6.5g corny and all worked out well. But only a few batches - I don't really know from that experience. So, what do you think I safe volume of wort is for a 10 gal corny (with blowoff followed by PRV ) ???

 

[BBBF]

@doug293cz - the analysis link above made me sit down, realizing I was overwhelmed by the breakdown of gases, pressures, etc. whoa. Very nice, and happy to be in awe. Wow.

So ... A question for this thread... If I am fermenting with a 10 gallon torpedo corny with a modified lid (w 1 1/2" TC)...
The corny is about 31" high.

I plan to ferment a lager at about 55°F, using a blowoff into starsan for the first few days, then a prv set to about 10-12 psi...
What volume of beer is okay for the fermenter batch size. My guess is 7.5-8 gallons but just a guess. I've fermented a 4.75 g batch in a 6.5g corny and all worked out well. But only a few batches - I don't really know from that experience. So, what do you think I safe volume of wort is for a 10 gal corny (with blowoff followed by PRV ) ???

The exact volume is going to be dependent on Fermentable, Temperature and Pressure, but your batch of beer is easily going to produce 20+ times the volume of CO2 vs. the liquid batch. I wouldn't trust a 1/2 gallon batch in a 10 gallon fermenter because of the gasses mixing, but I wouldn't fear 5 gallons.