Secondary FV beer explosion?

[Gawain]

Hi all,
I'm in the final straight (I hope) of my first brew. A kit IPA which had an OG of 1040 and a FG of 1008 when racked into a plastic pressure barrel (with tap). I added 80g of sugar dissolved to aide the secondary fermentation process and let it sit for a week at constant 18c indoors.

Everything seemed to be going fine, except on Sunday (2 days ago) I moved the barrel into an outside shed to cold condition. I have a digital thermometer in the shed (not in the barrel) and noticed the temp never dropped below 5.4c and is usually around 8c at present, which I thought were ideal conditions.

When I checked this morning at 9am, all was okay and the temp was around 6c in the shed (the barrel stick on thermometer only shows 12C and above so not sure exact brew temp). However when it was checked again at 12pm beer has exploded all over the shelf above the barrel and the old blanket it is sitting on is soaked.

There is minimum liquid loss in the barrel, but obviously a pint or so all over the blanket. My question is what exactly would have caused this? Has fermentation not completed? There was plenty of headroom in the barrel once it was racked and I didn't think cold conditioning would cause this to happen. Could it be the barrel warming up during the day from the cooler temp overnight has reactivated the yeast?

How do I prevent more exploding liquid? Draw a couple of pints to relieve pressure? Move back indoors where temp is constant and controlled (although it will be less than ideal drinking at that temp).

Any advice much appreciated. The whole process has been going on nearly 5 weeks now and I hope nothing I've done has ruined the brew.

 

[cheshirehomebrew]

You said the FG was 1008 but how long was this stable for? its entirely possible fermentation hadnt stopped (technically levelled out) and the addition of the extra 80g of sugar kicked it off again

glad not much was lost though !

 

[Gawain]

Thanks for the quick response. It was steady from the Friday - Sunday, which is when I racked it into the pressure barrel.

Just as a visual aide, here is the headroom the barrel head when first racked and after the "explosion" (if that's the right term?)

After racking:

After explosion:

 

[Brewtus]

Looks to me like a poor seal at the tap couldn't handle the pressure of carbonation and leaked.

 

[Cwrw666]

I've got a couple of PBs like this and they both tend to suffer from drips from the tap and one of them from the rubber seal where the tap screws into the barrel. If it's the latter - you would see drips of beer from around the rubber seal - tip the barrel on it's back, open the tap to let the gas out, unscrew the tap from the barrel and wrap the threads in lots of PTFE tape (from jewsons or somewhere similar) and screw it back in. In my case this has worked but has needed to be done both times I've used it since. You may have to re prime the barrel.
By the way I always stand my PBs in a roasting tray when I've just filled them just in case they leak.

 

[Brewtus]

Looks to me like a poor seal at the tap couldn't handle the pressure of carbonation and leaked.

 

[Gawain]

Thanks for your comments all. I really don't think the tap has leaked. The shelf above the barrel was covered with beer which leads me to believe pressure (and beer) was forced out of the valve in the screw top. Though it may have leaked through the tap also, I see no sign of this around the tap itself.

I have brought the brew back indoors and leaving it to settle at a constant temp now. So far, no further explosions. But I have drawn a (very gassy) pint and released a bit of pressure from the top.

I'm still confused how this happened during cold conditioning, I am quite certain fermentation had stopped, but I guess maybe not. Will be tasting for the first time Sunday so fingers crossed.