Gravity stuck at 1.020?

Ingredients
1

I’ve never seen this before. Brewed a clone of Deschutes Black Butte Porter, all grain, English ESB wet yeast from Community Cultures Yeast Lab (San Antonio) on Sunday. In the fermentor by 6pm. Bubbling in the Airlock in less than 24 hours. Bubbles slowed by late Wednesday night. Airlock still bubbling at same slowed rate today, Friday morning. Using a Tilt Hydrometer & Thermometer. Been fermenting at 68°F. OG: 1.050. Tilt has reported current gravity to be 1.020 for over 36 hours. Is that possible if CO2 is still gassing off? Did my yeast putter out? Think the Tilt is wrong? It has been flawless in the past. Should I pitch additional yeast?

2

Tilt is notoriously inaccurate once there is any yeast and/or hops stuck to it at end of fermentation.  You cannot trust it to be very accurate, only to tell you when FG is stable.

English yeasts are also well known to have low attenuation.

You probably are experiencing a combination of both factors.

EDIT:

No need to add any more yeast necessarily, unless perhaps the attenuation and ABV turns out to be much worse than you had anticipated, then it might not hurt.  But I would recommend measuring with a clean hydrometer before you do that.

Also… did the recipe contain any lactose?  That could explain part of the issue as well.  Lactose is unfermentable.

3

BBP is a porter and does not have lactose.

4

Sometimes when my Tilt gets glommed up or stuck against the side of the fermenter, a gentle jiggle or swirl of the fermenter is enough to free it up.

5

Think the Tilt is wrong?

My guess is it probably is the tilt. It will give false reading due to yeast caking, Co2 and not properly tared (is that even a word?). With that said, I tared mine last Sunday, set it up per color and beer, sanitized and plopped into the fermenter only to give me an instant read of 1.006 Next day it gave the same read. Clearly a failure. Weakening battery? possible but doubtful.

Take a sample and check with a hydrometer.

6

It was the Tilt.  Need to calibrate the thing.  Current gravity is between 1.017 and 1.018.  I’m saved!  Thanks for the help!

7

Once fermentation starts, I only rely on TILT to tell me when fermentation is complete.