Help, I think my fermentation has stalled!

[Erik the Anglophile]

So, I am fermenting a porter (OG 1.064) that I brewed last saturday. I pitched a pack of m15 empire ale yeast and it kicked off in just 4 hrs.
Took a test tuasday night and it was a tie between 1.023 and 24, and another today(thursday) around noon and it seemed to be 1.022-1.023, so pretty much the same.
I first thougt I might have under-pitched, but 1 pack of yeast for just above 9 liter of OG 1.064 should be sufficient?
Should I stir the bucket a bit or just accept that this yeast might come out low attenuated and not be a good yeast for beer with a little higher gravity and bottle it next weekend if there doesn't seem to happen anything in the coming days?
Also thinking of using another strain next time I brew this recipe, thinking about m42 new world strong ale at 19-20c or s-04 at 18c.

 

[BrewnWKopperKat]

How did you measure FG (hydrometer? refractometer?)

What did you use for estimated attenuation to estimate FG?

edit: also, recipe and mash characteristics would be helpful.

 

[Erik the Anglophile]

How did you measure FG (hydrometer? refractometer?)

What did you use for estimated attenuation to estimate FG?

Measured with my hydrometer, it has markings every 0.2 steps (1.050-1.052 and so on) and is tricky to read sometimes, gonna get a more exact one.

Used beersmith and it calculated the FG to around 1.015(70-75%attenuation)

I have read this strain may have some problems with low attenuation, especially in higher gravities, and is prone to stalling for a few days and then picking up again and finishing the leftovers.
Also mashed at 66c for 90 mins to account for this if it matters.
Just wondering if I should dismiss it as the strains low attenuation problems or keep it at the same temp and just wait and see for a couple of days?
I calculated the abv to be 5.4% as opposed to est 6.4% so it has evidently fermented the majority of fermentable sugars by now.

 

[BrewnWKopperKat]

it [estimated] the FG to around 1.015 (70-75%attenuation)

It appears it used 75% to estimate FG. Using 70% attenuation, estimated FG would be around 20.

If you have limited experience with this strain of yeast in this recipe, it may be reasonable to let it sit for a while to see what happens.

 

[Erik the Anglophile]

Yeah, gonna take a new test sometime on sunday, and if it hasn't changed I'll let it sit and clean up for a while and bottle sometime by the end of next week.
It tastes pretty decent already, some trace amounts of acetaldehyde and a smaaaall tart flavor, but that's probably because it's still so fresh and nothing a little bottle conditioning won't fix.
Thanks for the help!

 

[VikeMan]

Used beersmith and it calculated the FG to around 1.015(70-75%attenuation)

Beersmith doesn't take the makeup of the grain bill into account when predicting attenuation. If you can provide the grain bill, I could tell you what BrewCipher says about it. (You already provided yeast strain, and mash temp/length.)

 

[Erik the Anglophile]

Beersmith doesn't take the makeup of the grain bill into account when predicting attenuation. If you can provide the grain bill, I could tell you what BrewCipher says about it. (You already provided yeast strain, and mash temp/length.)

2.49kg 81% maris otter
310g Crystal 10% 150/UK light crystal (~170 ebc)
180g 6% low colour chocolate
90g 3% UK black malt
mashed at around 2.7 liter water/kg of malt

 

[VikeMan]

^ I ran this through BrewCipher. I would predict ~1.017 FG.

 

[Erik the Anglophile]

so a bit of under attenuation or possibly stalled fermentation, I'll wait until sunday and see if anything has happened then.
probably gonna use m42 and nottingham as my go to for stouts/porters and stronger ales from now on...

 

[VikeMan]

so a bit of under attenuation or possibly stalled fermentation, I'll wait until sunday and see if anything has happened then.

Based on what you've said so far, it sounds like it's still moving, but slowly. Personally, I'd try to be patient, especially at only 5 days in.

 

[Erik the Anglophile]

Based on what you've said so far, it sounds like it's still moving, but slowly. Personally, I'd try to be patient, especially at only 5 days in.

meant I'll wait till sunday and take a SG test then, to see if there has been eny fermentation going since today.

Edit: Checked the bucket and there is still some co2 production in there, saw the lid had a small budge and it looked lika a bubble was on its way out of the airlock, so it might very well still be some low activity in there, I'll have to see how it develops.

 

[Erik the Anglophile]

Update: Checked the gravity last saturday and this monday, it had stabilised at 1.023. Gonna bottle it tomorrow night, it tasted pretty good, altough a little weaker and a bit sweeter than anticipated. Also found out that my thermometer shows 2c under the actual temp, so my 66c mash was actually a 68c mash, this might have been a co-conspirator in this. But no worries, now i know to adjust for this in coming brews.