Craftbrewer English yeast - stuck fermentation

[big78sam]

I brewed an AG Rye robust porter almost 4 weeks ago. It had an sg of 1068. I was running short of time so didn't have time to hit the wort with 02 or use a starter so I just sprinkled 2 packets (not rehydrated) into a 20L brew. I know that's not ideal but I've done this plenty of times in bigger beers with us-05 or the craftbrewer American ale yeast with no issues before. It was off and going 24 post pitching.

After 2 weeks it was 1026 so I increased the temp from 18.5 to 19.5. 2 weeks later it's dropped to 1023. I increased the temp to 20.5 today and swirled the fermenter to rouse the yeast. If that doesn't work I'm at the point of putting some us05 onto the stir plate and pitching it at full krausen.

I've never had to rouse yeast before so how vigorous do I need to be? Is it worth sanitising an erlenmeyer flask and trying to get a few litres of trub/yeast mixture from the bottom of the fermenter through the tap and back into the top of the brew? Has anyone has issues with this yeast dropping out and stalling early before?

 

[MHB]

I think there isn't a yeast that hasn't been blamed for dropping out or stalling early. Truth is its not the yeast at least 99% of the time it the brewer not the yeast.
You are at about 66% apparent attenuation, true that's short of where you would expect that yeast (well its probably S-04) but not way short.
Once a yeast gets going it usually takes some sort of event to pull it up short. Apart from the obvious ones of the yeast running out of food (finished) or reaching its attenuation limit.
Thangs that will cause yeast to stall are, sudden cooling, yeast hates rapid temperature changes, you clearly have temperature control but if you have the sensor in the wrong place you can make the temperature jump up and down this can upset the yeast. Being too cool, get too close to the bottom of the yeasts working range and it might give up early. Try bumping the temperature up to 22-23oC leaving it sit for a day then giving it a swirl to get it going.
The other big cause is people not really mashing at the temperature they think they are. If your mash measurement is off you could easily make a beer with an 66% AA limit. Well worth calibrating whatever you measure you mash with.
Said it before but every brewer should have one good lab grade glass thermometer to use as a reference.
I know its tempting to blame the yeast, in truth its rarely the problem, take a long hard look at your processes odds on the answer is there somewhere.
Mark

 

[yankinoz]

Craftbrewer English yeast is a blend. It's highly unlikely they all quit. For sure you did not underpitch.

Re MHB's note about mash temps, I'd add a sales pitch for doing Hochkurz matches, and yes, even on English styles.

 

[big78sam]

Thanks for the responses. Its a new thermometer (2nd brew only) so that could be the cause. The first brew was ok and it was the same mash temp (65.5, dropping to 64 after 75 minutes)

I get that there needs to be a "cause" but this is the first time I'd used that yeast so wasn't sure if it was prone to floc out early and stop. Some yeasts are more touchy than others. If I'd pitched 2 packs of Nottingham and it stopped I'd be more confident that was a far as it was going to go. I've increased the temp to 22 and will give it a rouse daily and see how it goes.

I did think about doing a forced ferment test in the stir plate as well but in the current cold weather temperature control might be problematic.

If it doesn't move I think I'll just throw a packet of nottigham at it.