I made this on Friday and now Sunday morning, the fermentation is enthusiastic to say the least. I'm glad I listened to the posts on this thread and put on a blow off tube rather than the airlock. It's already blown the stopper out once and every now and then gives a big rumble and a bunch of bubbles come out of the tube.
The OG came out at 1.073 into the fermenter, which is way high, with a brewhouse efficiency (according to BrewTarget) of 84%.
This is my tenth batch so still a relative newbie, my previous nine batches averaged at 70% with variance between 63% and 76%.
I'm sure I'll end up with beer (worst case). I'd like to try and understand the cause for the jump in efficiency.
Two possible causes: 1) Grain crush. When I picked up my order from the LHBS, they had crushed the grain even though the instructions on the order were to NOT crush. I have a corona mill and have been crushing my own grain for the past 6-7 batches. There didn't appear to be a lot of flour in the crush, certainly less than when I use the corona mill.
2) Temperature of the mash. I really screwed the pooch on my temperatures this time. I've started trying to dial in my temps a lot closer, but really messed this one up. I heat the strike water to about 155 and then preheat the 10 gal igloo cooler MT. When the strike water reaches 170F, then I mix the remaining strike water in the cooler and adjust as needed to get to the right temp. In this case it called for 166F, since my grain temp was a little colder at 65F I adjusted the strike water to 168F.
After mashing in, I was watching the mash temp and it only went down to 167F. I stirred a little more and then said WTF, I better add some cold water. That brought the temp down to 165F...bloody hell! So I added more cold water and then ice, before the temp started falling. About that time I realized there was a glob of mash stuck around the end of the temp probe..so after stirring and moving the probe around, the temp ended up at 146F. Crap...so then I started adding boiling water to bring the temp back up, finally got it to 151F, now with the mash at the 8 gallon mark in the cooler.
Let it mash for 60 mins from this point, temp ended up at 146F. Normally, with preheating the MT, my temps will only drop 1F during the 60 mins.
1st runnings came to almost 6 gallons, so I added 2 gallons of sparge water and ended up with 7.75 gallons in the BK.
Preboil gravity ended up at 1.050, then post boil with the malto dextrin addition came to 1.073.
So based on what I've read (and hopefully understand) thanks to everyone on this forum, the lower temps will cause an increase in the fermentable sugar, as well as the longer mash time (took about 20 mins futzing about with the temp after the grain was added to the mash water).
Could the thinner mash also have contributed?
Lesson learned..always stir the mash well, move the temp probe around in the mash and give the temps a couple of minutes to settle out before you start making adjustments! Anything else I should take away from this one?