Excess Foam When Priming

[Julez]

Hi all,

I've read some past posts on this issue, but can't quite figure out what's going on in my case.

I've had a lager in the fermenter for a few weeks, which has been sitting on a gravity of 1.012 for well over a week - i.e. it's finished (or so I thought). A week ago, I did a diacetyl rest at 15 degrees C, where it sat for two days, then I dropped the temp down to 2 degrees to try to clear out the yeast as much as poss before bottling.

I normally use carb drops, but ran out, so used dextrose instead for bottle priming (4.5 grams/tallie). The beer foamed quite a lot when filling the bottles. Now, I've read this is due to either the beer not being finished, or excess CO2 remaining in solution, that reacts with the dex. when bottling. I'm assuming it must be the latter. I tried swirling the fermenter a few times, to release some CO2, then left it overnight before trying again, but the same problem persisted. I went ahead and finished bottling anyway. Even when there was just dregs left in the bottom, I put the fermenter lid back on (with airlock) and bugger me if the thing started bubbling away as if it was a fresh batch of unfermented wort!

My question is, what causes excess CO2 in solution and how do you get rid of it or prevent it from building up to excess?

Cheers, Julez.

 

[PostModern]

The colder the beer is fermented, the more CO2 will remain in solution. Seeing as you diacetyl rest was 15C (ie the max temperature of the beer), that will leave about 1 volume of CO2 in the beer before you even prime it. No need to get rid of the excess, just prime accordingly. If you bulk prime with boiled dextrose (or whatever), there will be no nucleation points for the CO2 in solution to foam up on.

 

[Julez]

The colder the beer is fermented, the more CO2 will remain in solution. Seeing as you diacetyl rest was 15C (ie the max temperature of the beer), that will leave about 1 volume of CO2 in the beer before you even prime it. No need to get rid of the excess, just prime accordingly. If you bulk prime with boiled dextrose (or whatever), there will be no nucleation points for the CO2 in solution to foam up on.

Thanks PoMo. After reading a lot of the other thread on this topic, I will be bulk-priming in future and using one of the priming calculators.

Cheers

 

[Steve]

Silly question i know but you did put the dex in the bottles first and then the wort? The other way around will result in foaming.
Cheers
Steve

 

[Bribie G]

I generally bulk prime but now and again - for example if my 25L vessel is tied up in the fridge doing a polyclar job or whatever, and the brew can be adequately bottled straight out of its current fermenter (Bottled a toucan stout for Christmas yesterday) then I'll bottle prime. I use 2L PET and 3 supermarket sugar cubes per bottle (reaches for flame proof suit ). Works absolutely brilliantly and gives totally consistent results at a fraction of the price of carb drops - but as described above the sugar gives 'nucleation' points for foaming and by the time I had finished the bottles all had a nice little Guinnessy head on top of the brew.

Nothing to worry about and not a sign that you are going to get bottle bombs.

Edit: of course as Steve says you wouldn't want to put the beer in first THEN add the sugar cubes - that could become nasty.

 

[Julez]

Silly question i know but you did put the dex in the bottles first and then the wort? The other way around will result in foaming.
Cheers
Steve

Yep, put the dex in first and used a racking cane too. From wider reading it seems to be a common thing when using dex when the beer has a lot of residual CO2.

 

[Julez]

Nothing to worry about and not a sign that you are going to get bottle bombs.

That's what I was worried about, but according to a priming calculator I just tried out, I will end up with about 2.7 volumes of CO2 for my lager, instead of around 2.5, due to the residual CO2. So the foam scared me a bit, but clearly the beer was finished, so it might just be a whisker more carbed than I had originally intended, but nothing out of the ball park. I hope that calculator is right!!