Underattenuation or stuck fermentation?

[Snrub]

Hi Everyone

I started AG brewing a couple of months ago, and my first (extremely successful!) brew was Palmer's Porter.

Last week I brewed this again, making up a yeast starter with WL007. The starter went as expected.

I use a RIMS system and usually set the temperature approx. 5 degrees higher than required before mashing in, however last week I overshot by approx 5 degrees resulting in a mash which starter at approx. 74 degrees and then dropped it to 68 over approx. 20 minutes.

After the boil, I found that my immersion chiller was broken, so opted for a 'no chill' approach and left the wort overnight in the room it's now fermenting in - ambient temperature around 18 degrees. The OG was 1.060.

After pitching, I got plenty of activity from around 4 hours and a 1 inch krausen after around 12 hours. So far so good, but after 24 hours I noticed the krausen had dropped significantly, and by 36 hours it was gone and the airlock had slowed significantly. I'm used to longer and more vigorous fermentations for my beers, and I'm sure the porter kept up for a few days last time out.

Without wanting to panic after just a couple of days, I left it till day 4 to measure the SG, which came out at 1.030, so far higher than I expected at that stage in the fermentation. The expected FG for the yeast is around 1.012-1.014 (based on the White Labs profile for WL007 - predicted 80%).

So on day 5 I rehydrated some Youngs Ale Yeast I had knocking about, pitched it, gave the wort a swirl and put a heating belt around the carboy. I can't say this made a massive difference - very few surface bubbles and very slow airlock activity - perhaps a bubble every 30 seconds or so. Yesterday (day 7), I took another hydro reading and got an SG of 1.028.

So, what advice do people have to proceed from here. I think the likely answer is "leave it a week and see," but being relatively new to AG I'm obviously curious! Some theories based on my reading:

1. I mashed at too high a temp and so the expected attenuation will be much reduced - can't remember where I read this, so if anyone can confirm/deny/expand that would be helpful.
2. I didn't aerate enough before pitching so the yeast didn't have enough oxygen to finish the job, so need more yeast.
3. I messed up just pitching the 2nd batch of yeast rehydrated, I needed to make up a starter to get the little guys working.
4. It's just a slow fermentation and I should chill out, leave it and see where it gets to.

Any advice or suggestions?

Thanks,
Snrub

 

[prog99]

Too many unfermentable sugars due to the high mash temps?

 

[foxbat]

(1) your mash temperature. After 20 minutes most of the conversion will have been done and so you have a lot of unfermentable sugars.

I would leave it as-is and chalk it up to experience but if you really want to raise the ABV to balance out the unexpected sweetness you could boil up some DME solution and add that. Not sure how much you'd need, I don't have access to the calculators where I am now.

 

[prog99]

Or since you've not much to lose throw in some amyloglucosidase enzyme

 

[Ghillie]

Or since you've not much to lose throw in some amyloglucosidase enzyme

Amylase enzyme?

 

[prog99]

Yes, I think I used the posh name for it.

 

[Snrub]

Thanks for the feedback guys. I think on balance I'll leave it for a while, make sure it ferments all it can, then chalk it up to experience. It's still beer!

Am I correct in assuming there's little risk of bottle bombs, given that the only fermentable sugars will be those I add for priming?