Bit of help needed

[Jon1964]

Recently put a brew into a Rotokeg, which has a schrader valve to measure pressure, and a brand new 4 inch cap

My thoughts are the beer is absorbing the co2 in the barrel (carbonisation) so the pressure keeps dropping
Here`s my notes
05.11.20 - 9.2 psi
06.11.20 - 7.4 psi - gassed up to 10 psi
07.11.20 - down to 4.2 psi so tightened top nut up and regassed to 10.8 psi
08.11.20 - 12.00 pm down to 4.4 psi so resealed with ptfe and regassed to 10.8 psi
08.11.20 - 1.30 pm down to 9 psi
08.11.20 - 2.50pm down to 8.4 psi

I`m thinking the 40 pints is absorbing so much of the co2, which would exsplain this
If I had a leak the pressure would drop to zero not stay at the 4 psi mark

I have my original Rotokeg cap as a back up, fitted with a new s30 valve - is it worth swapping out the caps if the pressure drops again to 4 psi ??

Cheers Jon

 

[Clint]

Where have you got the keg? Mine seem to absorb more as they get colder as they're out in the shed. Or you have a leak!?

 

[MmmBeer]

If temperature reduces in a fixed volume, the pressure will drop too. - Gay Lussac's Law

 

[Jon1964]

In a spare bedroom - temp may have dropped a couple of degrees

 

[Jon1964]

I`m thinking the threads are slightly different on the Balliihoo 4 inch cap to the original Rotokeg cap
If it drops down to 4 psi again I will swop out the caps

 

[The-Engineer-That-Brews]

Spray a bit of strong washing up liquid solution on it and see if you can spot any bubbles?

 

[The-Engineer-That-Brews]

The pressure certainly will drop, as the beer absorbs CO2 - and the amount and rate of that drop will be much faster if the keg is very nearly full with only a small headspace.

 

[The-Engineer-That-Brews]

If temperature reduces in a fixed volume, the pressure will drop too. - Gay Lussac's Law

Also, cold fluids absorb more gas

 

[Jon1964]

The pressure certainly will drop, as the beer absorbs CO2 - and the amount and rate of that drop will be much faster if the keg is very nearly full with only a small headspace.

It`s a 40 pint brew so not that much headspace - i will keep monitoring it
Cheers Jon

 

[Buffers brewery]

When I was doing some leak testing recently on my King Kegs with a near full Keg, almost 6 gallons of water, I pressurised to 10 p.s.i. with CO2. 10 hours later the pressure was 4 p.s.i. I checked the cap under water (in an adapted water butt) and there were no leaks. I repressurised with air. There was a small drop over several hours, probably the last of the CO2 being absorbed. Third repressurisation with air resulted in no further pressure drops.

 

[Jon1964]

When I was doing some leak testing recently on my King Kegs with a near full Keg, almost 6 gallons of water, I pressurised to 10 p.s.i. with CO2. 10 hours later the pressure was 4 p.s.i. I checked the cap under water (in an adapted water butt) and there were no leaks. I repressurised with air. There was a small drop over several hours, probably the last of the CO2 being absorbed. Third repressurisation with air resulted in no further pressure drops.

Thanks Buffers, so my understanding is that the beer will absorb upto a certain amount of co2, then provided nothing is drawn out, then the psi should remain static, give or take for temperature changes

 

[peebee]

As you have said; "My thoughts are the beer is absorbing the co2 ...". And @The-Engineer-That-Brews hinted at it too.

I get the impression you are attempting to "force carbonate" your beer? That 10psi is about the maximum a plastic Rotokeg will take? That will be about 1.7 "volumes" of CO2. That you haven't got a reliable regulator to leave the CO2 attached (which if you have a leak you definitely don't want to do!)?

The nice thing about using "volumes" to measure the gas content is it is very easy to visualise. So lets say your beer has 0.9 volumes of dissolved CO2 (it'll actually have about 0.85-0.9 - "saturation" at atmospheric pressure) so you need to add about 0.8 volumes of CO2. So you pressure up the headspace with 10psi and the headspace is about 10% of the keg's volume. 10PSI is about 2/3 of atmospheric pressure, say 4/5 to keep the visualisation easy. So the first pressurisation will put about 10% of the required 0.8 volumes (4/5 of one volume) into the beer ...

See where this is going?

But you also want to be sure of no leaks! Priming is the way to go with plastic pressure barrels. Being careful not to overdo it! The extra gas is just used to keep the pressure topped up while serving.

 

[Buffers brewery]

Thanks Buffers, so my understanding is that the beer will absorb upto a certain amount of co2, then provided nothing is drawn out, then the psi should remain static, give or take for temperature changes

Yes. But as @peebee says, usual practice with a plastic pressure barrel is to prime the fermented beer on transfer from your fermentation bucket with sugar solution. I flush the headspace in my barrel with CO2 after transfer and pressurise to around 3 p.s.i. The fermentation that takes place in the barrel will generate CO2 and increase the pressure, so you need to be careful how much you use and make sure your pressure relief system is working.

 

[Jon1964]

As you have said; "My thoughts are the beer is absorbing the co2 ...". And @The-Engineer-That-Brews hinted at it too.

I get the impression you are attempting to "force carbonate" your beer? That 10psi is about the maximum a plastic Rotokeg will take? That will be about 1.7 "volumes" of CO2. That you haven't got a reliable regulator to leave the CO2 attached (which if you have a leak you definitely don't want to do!)?

The nice thing about using "volumes" to measure the gas content is it is very easy to visualise. So lets say your beer has 0.9 volumes of dissolved CO2 (it'll actually have about 0.85-0.9 - "saturation" at atmospheric pressure) so you need to add about 0.8 volumes of CO2. So you pressure up the headspace with 10psi and the headspace is about 10% of the keg's volume. 10PSI is about 2/3 of atmospheric pressure, say 4/5 to keep the visualisation easy. So the first pressurisation will put about 10% of the required 0.8 volumes (4/5 of one volume) into the beer ...

See where this is going?

But you also want to be sure of no leaks! Priming is the way to go with plastic pressure barrels. Being careful not to overdo it! The extra gas is just used to keep the pressure topped up while serving.

I`m not force carbonating, I just couldn`t get my head round why the psi had been dropping.
You lost me with the volumes bit BTW

 

[Buffers brewery]

I`m not force carbonating

So have you primed your beer with sugar solution?

 

[Jon1964]

So have you primed your beer with sugar solution?

Yep Buffer, primed with 100 g, but had to unseal the cap some days after as the top tap float had got itself upside down and was just drawing gas out when i went for a sample taste - hence wht I had to use the gas to repressurise

 

[Buffers brewery]

Yep Buffer, primed with 100 g, but had to unseal the cap some days after as the top tap float had got itself upside down and was just drawing gas out when i went for a sample taste - hence wht I had to use the gas to repressurise

Ok, so if you've got everything sealed up again the pressure should settle. Check your Schrader valve, I've had them leak on me. That's why I changed to corny posts. I also have a pressure gauge fitted to my tops.

 

[peebee]

I`m not force carbonating, I just couldn`t get my head round why the psi had been dropping.
You lost me with the volumes bit BTW

Sorry, just that "volumes" seems to be that way everyone describes carbonation levels these days. And you are not force carbonating? You even say "primed with 100g", quite enough to generate the CO2 needed to burst the barrel! That pretty well provides the proof that the barrel is leaking gas!

 

[Jon1964]

Sorry, just that "volumes" seems to be that way everyone describes carbonation levels these days. And you are not force carbonating? You even say "primed with 100g", quite enough to generate the CO2 needed to burst the barrel! That pretty well provides the proof that the barrel is leaking gas!

The kit was Youngs American IPA - I followed the instructions to the letter, I quote
"BOTTLING AND/OR BARRELING YOUR BEER 14. If bottling syphon beer into another sterilised vessel, then dissolve your primary sugar by stirring the brew. Once dissolved you can now syphon into your bottles. This method will guarantee an even spread in each bottle.If barrelling, add your priming sugar directly into the barrel then syphon beer directly from your bucket. "
Actually I weighed the priming sugar bag, think it was 115g of Dextrose - not Household granulated, so perfectly fine I believe
(I always used to use 4oz of priming suger 25 years ago without exploding a barrel - I brewed 77 kits without priming problems)
Cheers Jon

 

[Buffers brewery]

I think what's happened here is your priming sugar has done it's thing but you've lost the pressure it produced cos you had to take the cap off to fix the float. You now need to re-establish that pressure. Assuming you DON'T have a leak you can either use gas or reprime, something I know @terrym has done when he used pressure barrels.