Calculating Priming Sugar After Pressure Fermenting

[Petrolhead]

Having just bought a Fermzilla All Rounder I brewed my first beer, a Landlord Clone, under pressure. Not the right beer for pressure fermenting but I had to use the new toy. The brew has been brewing for around three or so weeks as I have been out of the country and thanks to my iSpindel I have kept an eye on things and fermentation is well finished.

As I have no free kegs, annoyingly one nearly empty, I am going to bottle the beer using a party tap straight from the Fermzilla. However, as I have brewed at 12psi and 20 deg I assume that the beer has some carbonation and I need to add a little to bring up to the right CO2 level.

I find that when I transfer a brew to the bottle after it has had a level of carbonation, usually when I nick a couple of pints from a keg, the carbonation drops so again I guess I need a small amount of sugar to increase the carbonation. Alternatively I could increase the psi in the Fermzilla for a couple of days and just transfer to the bottles but the beer will then foam and cause bottling problems.

Finally, whilst the Fermzilla held its pressure when fermenting I have a suspicion that after fermentation finished that the pressure may have dropped, the extended period in the fv may have added to this. So if pressure has dropped to nil can I just do the normal priming calculation?

Sorry for the long question which many of you would have known where I was heading right at the beginning but thanks in advance for any suggestions.

 

[uDicko]

Well done on the fermzilla :) great compact bit of kit.

So if pressure has dropped to nil can I just do the normal priming calculation?

Yes if you are totally sure there is no carbonation in the liquid, id say its safe to use normal methods of priming. If it does have carbonation then no.

Alternatively I could increase the psi in the Fermzilla for a couple of days and just transfer to the bottles but the beer will then foam and cause bottling problems.

Id do this personally. Get as much measured carbonation in the fermzilla and when you are happy, move to keg and/or bottles.

When it comes to the bottles, do you use normal glass or screwtop PET?

 

[uDicko]

As a side note, if you do use PET or plan to move to it (awesome for transferring under pressure to bottles) then getting one of these: Plastic Fermzilla / Carbonation Cap
and a small piece of tubing to reach to the bottom of the bottle makes for a great addition. Just need to unscrew the cap slightly to equalise the pressure and you are filling pretty quick

 

[peebee]

… Finally, whilst the Fermzilla held its pressure when fermenting I have a suspicion that after fermentation finished that the pressure may have dropped, the extended period in the fv may have added to this. So if pressure has dropped to nil can I just do the normal priming calculation? …

There shouldn't be any suspicion? The Fermzilla can be used to serve the beer out of if you really wanted and after only 3 weeks even small gas leaks wont have had much impression. If you are using the "common" naff poppet spunding valve they do have a habit of failing to seat and seal properly after venting (if so, get a different design!).

Otherwise, guessing will do the job as it is hardly a precision task: About half (or less) of your usual sugar amount (say 1/4tsp per pint/500ml) shouldn't harm

 

[Drunkula]

If you go here you can work out the residual co2 in the beer for pressure fermenting.
https://jollygoodbeer.co.uk/wp-content/uploads/2016/03/JollyGoodBeer_PSI_Chart_for_CO2.pdfYou'll have 2.0 volumes rather than the 0.86 residual vols you'd have brewing without pressure.

Ignoring the degassing of the headspace for now let's imagine you brewed as you did but want 2.3 volumes of carbonation. Go here :

https://www.brewersfriend.com/beer-priming-calculator/and enter 53.93c as the brewing temp - which wrongly puts in 1.00 residual volumes, just go with it because it makes life easier.

Now put into the desired vols (vols co2 required - vols you have + 1) -> (2.3 - 2.0 + 1) = 1.3
That gives 27.6g of sugar for 23 litres. I'd definitely be making that into a solution.

When you dry hop and open the lid the headspace co2 will drop and eventually the beer will offgas into it - I can't be faffed with the calcs but if you had a pressure gauge you could use that figure for the first step once it had equalised - or just pressurise it back to 12psi.

 

[Petrolhead]

@peebee my suspicion was only due to the fact that I was away and didn’t know if the fv was loosing pressure as it was new. Got back tonight and the spunding valve was set to 12psi but it had dropped to 4 psi so a small leak.

I have bought the pressure kit but it has the metal valves so I may follow @uDicko advice and fit the plastic caps.

Fantastic and perfect advice @Drunkula as always and I will enjoy getting my head around things but I may take the easy way out on this occasion and just add less sugar when priming as @peebee advises.

Thanks to you all.

 

[uDicko]

Metal valves are fine on the lid of the fermzilla. I use one carbonation cap to screw onto plastic bottles and pressure transfer to the PET bottle, coke bottle etc you can get the T cap for a bit extra cash but I think its largely unnecessary

 

[Petrolhead]

Sorry I should have answered your earlier question, I use 500ml glass bottles and run three kegs. Actually want to buy a few more.