What could be causing slow yeast (not a starting question)

[HiGravShawn]

I recently brewed a partial mash IPA very similar recipe to ones I've done before and I used my Pacman harvest. It's second gen and I harvested about 5 vials for freezing and this problem has never happened with the other three I've used although this is about 5 months old. I used yeast nutrient too. So the gist of the problem is I started it as normal up to 2L and saw nothing weird. I dropped the initial wort to like 60ish so it started slightly slow. I let it rise slowly overnight to 65F and stabilized it though and it's stayed in the 64-66 range in a cooler for three weeks today. Within four days I had strong activity in blow off tube. It has been expelling bubbles about every 6 seconds non-stop, but since usually I'm way finished by now I did a hydrometer reading and got 1.040!? At this rate it's barely half done!

TLDR; Normal start, normal brew, normal recipe and yeast, strong activity the whole time, but after three weeks it's barely half done. What is up wit dat?

 

[theredben]

Have you independently checked the temperature of the wort?

 

[HiGravShawn]

Yeah there's a thermometer on the carboy and checked the temp when I got hydrometer reading.

 

[sjbeerman]

It sounds like you possibly had a population of unhealthy yeast cells, possibly due to the age and number of generations. If that was the case then I would have made a lower gravity starter and stepped it up from there.

 

[HiGravShawn]

I did a smooth starter. I went from 300ml @ about 1.030 and doubled it while upping the gravity to 600ml and then 1200ml and then a little over 2L @ about 1.050. It was going like mad when I pitched.

I did remember something though. I usually use nothing but extra light DME when I use extract and design the color and flavor with grains, but this time I tried Amber DME. I would think if anything it could have more un-fermentables and stop high and sweet, but just slow? Not sure if it's that or just the yeast.

I guess I'll know more once it's done and I can taste it and see how it comes out.

 

[a10t2]

Have you calibrated your hydrometer, or tried a second hydrometer?

 

[HiGravShawn]

Only one hydrometer, but it's calibrated. Plus I brewed again last night and it matched up with the refractometer.

 

[PseudoChef]

How are you oxygenating the wort? Also, was the temp of the yeast culture the same as the wort at pitching?

 

[HiGravShawn]

Unfortunately I don't have an aeration system so it's just a few minutes of vigorous shaking. The temps should have been pretty close.

Around the time of the original post I shook it up real well and it seemed to speed up significantly and the bubbles seem larger so maybe it's been really slow and I couldn't tell. I could see it bubbling every 6-8 seconds, but didn't really have a basis of comparison on the size of the bubbles or anything. As of this morning it was still pushing bubbles out in the sanitized catch container. I guess this guy is going to end up in primary for about 28 days before dry hopping.

 

[ccudc9]

It's second gen and I harvested about 5 vials for freezing

How were these vials stored and where? Also, what was your OG?

 

[HiGravShawn]

I don't have the OG with me here at work, but I'd guess around 1.068 to 1.070. The vials were stored with glycerin in the freezer the same as always. Last night I removed the blow off since it hasn't been pushing krausen up for the last week or so and the air lock immediately started going like crazy. Weird brew.

 

[ccudc9]

If I were you, I would pull out 500ml or so with a little bit of krausen, and force ferment it. Swirl it as much as you can, and keep it 80+. See what you gravity is after a day or so, and see what you get.

 

[bannonb]

for aeration, just slosh around the wort in your fermenter. I do this for 5 minutes and usually have a krausen raised, then I pitch. Works great.

Since your starter went well and I assume you had a nice layer of white yeast cake, that part obviously went OK. You pitched at high krausen, so that's good.

Did you pitch the entire starter or did you drain off the wort and just pitch the slurry?

Pitch more yeast and call me in the morning

Really I'm stumped. Please post your outcome.

 

[HiGravShawn]

So still bubbling at 2 seconds and starting to throw off my brew schedule. Not too worried though, it smells great!