Milk Stout - Carbonation Issues

[andyn2001]

I've made three Milk Stouts is the last year, all bottled:

1. First one, priming sugar level 1.8vols - extreme fobbing through over carbonation
2. Second one, priming sugar level 1.5 vols - same result
3. Third attempt - zero priming sugar. Opened one today beer fizzed out of the bottle!!! I had noticed it getting carbed over the last 2 weeks.


Now, first two attempts I assumed I had bottled when fermentation was not complete, so for the third attempt I waited 3 weeks before bottling and had a steady gravity reading for over a week.

Today I took a gravity reading of this now fizzy stout it was 1.010, 6 weeks ago on bottling day it 1.015, so it has obviously carried on fermenting.

My question is this, is it the lactose sugar, it's meant to be something like 99% unfermentable,
but can yeast slowly break it down over time??

Or, do I need to leave the stout more than 3 weeks before bottling.....if it's still fermenting 9 weeks after brew day, how long do I wait?!!

Anyone else had similar with milk stouts?

 

[MyQul]

Whenever I make stout/porters I never use priming sugar. Yeast seems to be able to scavenge a bit more sugars from the wort/beer enough to carbonate to low (English beer) levels.
However it sounds like you may have a wild yeast infect as it's happened to three beers in a row. Wild yeast can slowly munch their way through any and all available sugars left in the wort till the gravity gets down to 1.000 or even lower, but without having any off flavours This happened to me once.
I'd maybe suggest bleaching your FV and other equipment, this is how I stopped the infection in my brewery(I oven my bottles as standard, so didnt need to do them),

 

[andyn2001]

I thought about wild yeast, but wouldn't my other beers also have the same prob, which they don't? However, I have just bought two new stainless steel fermenters and will brew next in one of them.

 

[MyQul]

Thats the thing I wasn't entirely clear on from your OP, whether it was ONLY your milk stouts and you'd made other beers in between. If you had made other beers in between the milk stouts, and it wasnt happening to them, then your right, it probably isnt a wild yeast infection

 

[andyn2001]

The mystery then thickens!

 

[Sandimas]

What yeast did you use?

I've just started using several of the Mangrove Jacks yeasts and the 2+2+2 rule goes out the window. I bottled my first one at 3 weeks and that was definitely too early, I watched the 2nd and 3rd ones like hawks and they were both still fermenting at the 3 week point. All different MJ yeasts.

 

[andyn2001]

Fermentis S-04, always for porters/stouts for me :)

 

[Sandimas]

Hmm S-04 is a quick one, usually done in 2 weeks.

Where are you storing the beer, and at what temp? I store mine in the garage which is fine 90% of the year, but with this warm weather they can foam a lot, I had a couple do it last night. Always happens with mine when we have a summer heatwave, I've had them explode before.

 

[andyn2001]

I ferment in a temp controlled fridge, at about 18C, then these have been in a cupboard at room temp once bottled, but with other beers that don't have this over carbing issue.......especially when no priming sugar was added.

 

[Sandimas]

I'm stumped then.

Only thing I'd say is that it happens, I've had it at various times over the years, some have been infections but some have been in explainable. I do think sometimes the ferment has a very long tail and, whilst it may have appeared to have stopped fermenting, it's chugging along very very slowly towards the end. Tends to happen more with darker beers in my experience too.

 

[andyn2001]

I agree to an extent, but I have two porters that I have primed with sugar, and they are fine months after bottling. It's just milk stout I'm getting this prob with. To go from 1.015 to 1.010 6 weeks after bottling is just mental.....I can only think the lactose sugar is being slowly fermented, but I can't find anything to back that up.

 

[Llamaman]

This probably isn’t possible, but could it be an infection in the bag of lactose? That would explain why each lactose beer gets infected, but why subsequent brews don’t (you clean the equipment afterwards).