dinnerstick wrote:i would look at fermentation rather than mash, in my experience a few degrees difference in the saccrification temp does not alter the fermentability to a great degree (ie not a 5 gravity point swing), and at 68 you have optimal alpha activity as well as some beta, it's going to convert quickly! i do lots of 'single infusion' type mashes at 68 (60 minutes) and get highly fermentable wort, which a good pitch of any self-respecting yeast can take down to the 1.010 range.
i have a few questions then, when you added dextrine (what was the dextrine, was it malto-dextrine? or pure glucose? the former is not hugely fermentable by brewer's yeast) how did you monitor the fermentation, did it give off gas or really change gravity?
what was the yeast, how old were the packs, could the temp have dropped, i'd look more toward these variables myself. did you oxygenate well, although dry yeast shouldn't need a lot of oxygen...
or, was this a wacky experiment with 30% crystal malt?? (<- not a highly serious question)
good luck!
Sorry I meant to write dextrose not dextrine, I've corrected in the original.
I thought the same about the mash temp also, this should not be a problem. I ferment in a temp controlled fridge which was at a steady 19 C and I increased the temp by a couple of degrees once I noticed it was stuck, so I've ruled that out, I only added the sugar yesterday so not had a chance to check gravity, but a quick look at the airlock shows it bubbling at a steady 1 per second rate and has been now for over 15 hours and it restarted very quickly once I added sugar, so fermenting normally again.
It could be the yeast that is a problem, however when I added some more of the same yeast nothing happened and given that it fermented 30 points in 48 hours, that is quite normal. It was only when I added the sugar that it started fermenting again (also had some fresh yeast in there from the earlier attempt to get it going). The yeast is NBS Ale yeast 2, which I believe is repackaged Mauri ale 514, no date on the package. I aerated well as always by shaking the hell out of the wort.
Everything points to it being a lack of fermentable sugar, there is a possibility that it could be that the temp probe on the BM is reading too low, I'll have to test that and I'm not going to rule out yeast........yet

There is about 10% crystal in the brew but that was added at 60 mins along with some black malt, so I can't see that having an effect.
EDIT: the beer has dropped to 1.018 today and fermentation is slowing, I think it will reach around 1.016 if I'm lucky, I'll get a 5% beer and I'll be happy with that, I didn't want a dry beer anyway :/