Irish stout fermentation

BIAB Recipe:
6 lbs 14 oz Maris Otter
2 lbs flaked barley
1 lbs roasted barley
5 oz black patent
Mashed at 152F, fermented at 66F OG 1.042 FG 1.011
The first time I brewed this recipe I used WL Irish yeast. Fermentation was great from the first week but after two weeks It just stopped. I raised the temp to 70 and roused the yeast, two weeks later gravity was still at 1.020. I pitched a package of Safale 04 and gave it two more weeks; after three hydrometer readings fermentation stopped at 1.016. Two weeks ago I brewed the recipe for the second time thinking that the problem was the Irish yeast. This time I used WLP 002 English Ale yeast. Took a hydrometer reading and the something happen 1.020. At this point I am not sure what it is going on. On both occasion I did a 2 L stater. Do I know that it's not the amount of yeast. Can some one help me understand this?
FirA

Could it be a recipe issue?

Neither the recipe or the yeast should be an issue. Have you tested the accuracy of your mash thermometer? Any chance you're using a refractometer for FG and not correcting for the alcohol?

dcp27 said:

Neither the recipe or the yeast should be an issue. Have you tested the accuracy of your mash thermometer? Any chance you're using a refractometer for FG and not correcting for the alcohol?

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I have a brewmometer that was just calibrated and I always double check with a digital thermometer and they are both accurate. I use a Refractometer throughout my brewing process just to check if i am on schedule to hit my numbers but both my OG and FG I get them by using a hydrometer.

I have read a couple of other threads and apparently that happens slot with stouts. Is it a common thing to get stock at 1.020?

Only thing I can think of is your mash temp. 1.011 is pretty dry, so maybe try mashing a little lower than 152. 150 or even 148 perhaps? That'll make for more fermentables in the wort. Just a thought.

Rake_Rocko said:

Only thing I can think of is your mash temp. 1.011 is pretty dry, so maybe try mashing a little lower than 152. 150 or even 148 perhaps? That'll make for more fermentables in the wort. Just a thought.

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Thanks, that's exactly what I am thinking. Appreciate the info.

If you are going to try and rebrew this beer repeatedly you have a great shot at doing a forced fermentation test. Save a pint if the wort and put it in a 2 liter flask or a quart mason jar. Sanitized of course. Then pitch a whopping amount of yeast in there. Like a half packet of US05. Shake it regularly and keep it really warm. 75-80F. After 5 days chill it to drop the yeast and check the gravity. If its lower than the main batch seems to be hitting you have a fermentation issue. If its the same then it's recipe/process driven. Make sense?

brewchez said:

If you are going to try and rebrew this beer repeatedly you have a great shot at doing a forced fermentation test. Save a pint if the wort and put it in a 2 liter flask or a quart mason jar. Sanitized of course. Then pitch a whopping amount of yeast in there. Like a half packet of US05. Shake it regularly and keep it really warm. 75-80F. After 5 days chill it to drop the yeast and check the gravity. If its lower than the main batch seems to be hitting you have a fermentation issue. If its the same then it's recipe/process driven. Make sense?

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I will try it the next time I brew this beer. I really want to get to the bottom of it. What is still a mystery is how already twice I have follow the recipe to a T, pitched the right amount of yeast and came out with the same results. Even more the fact that I have read in a couple of threads that it is a common thing for fermentation to stop @ 1.020 with stouts.
Thanks for the info.

Rake_Rocko said:

Only thing I can think of is your mash temp. 1.011 is pretty dry, so maybe try mashing a little lower than 152. 150 or even 148 perhaps? That'll make for more fermentables in the wort. Just a thought.

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while 1.011 is pretty dry, it's actually on the high end for a dry stout, plus this is only a 1.042 OG, so that's only 74% attenuation. that should easily be reached with a 152F mash (I tend to get around 78% with 002 at that temp). every system is diff tho, so it's possible the OP does need to lower it.

Paquitin said:

Even more the fact that I have read in a couple of threads that it is a common thing for fermentation to stop @ 1.020 with stouts.

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no idea who is saying that, but its wrong. you can't lump all stouts together. 1.02 is good for a RIS or milk stout, but its way wrong for a dry stout. I just made a milk stout with a similar strain (Wy1318) and it went from 1.072 to 1.023 with 1lb of lactose (so really like 1.014 if you take out the lactose) and mashed at 153F.