Unusual stuck fermentation

[belgbrew]

Hello everyone
First time writer - long time reader)

I'm brewing a couple of years now, but first time got a stuck fermentation.

This time I brewed a Belgian Trippel with OG 1.084 (20.0 Plato) and fermented with WLP540 yeast. Pitched propagated (15 Mln/mL) yeast at 66°F (19°C) and raised during fermentation to 73°F (23 °C).
Aeration by shaking the vessel.
Fermentation started in a few hours and was quite vigorous.
After a week of primary I got only roughly 50% apparent attenuation - 1.041 (10.2 Plato)
I left the beer to ferment one more week but the gravity fell down only to 1.034 (8.6 Plato) - ~60% AA, so I made another starter and pitched it (10 Mln/mL) again aerated by shaking - but the gravity still stays the same after another week.

Temperature is ok, pitching rate is ok, aeration is ok...
What's wrong with it? Is there any solutions to the problems? It could be my first batch to dump...

Here's the grist:
Pilsen 9.9 lbs (4.5kg)
Cara Gold 0.9 lbs (0.4kg)
Cassonade Dark (Candico) - 2.2Lbs (1 kg) - 10 min boil
Dextrose - 1.3lbs (0.6kg) - 10 min boil

Mash schedule ("Rochefortish"):
15 min 126°F (52°C)
35 min 145°F (63°C)
25 min 165°F (74°C)
mash out 172°F (78°C)

Mash thickness 3 L/kg


Thank you in advance for any help

 

[hercher]

I would just give it more time. You probably should not have aerated a second time, as introducing oxygen at that stage could lead to stale off-flavors in your beer. I'm not certain why you would have mashed at 165 for 25 minutes -- you pretty much stopped all enzymatic activity at that point. So it could be that you have a lot of unfermentables in your beer. If it stays stuck, try adding some beta amylase.

 

[belgbrew]

This schedule is from BLAM
Yeah 165(74) is on the upper limit but altogether with ramping the saccharification phase was nearly to 60 mins(temp in between 140-158°F ( 61-70°C), that usually is enough for conversion
Iodine test also was ok...

 

[belgbrew]

Ok guys, 2 weeks after the gravity is 1.012 (3°P) - 85% AA - close to what I 've expected
That was the longest fermentation I've ever had - 4 weeks - really really odd

 

[TNGabe]

I'd say you either didn't ramp the temp up enough or ramp it up soon enough and I'd guess the latter.

 

[hercher]

How was the flavor?

 

[belgbrew]

The flavor is marvelous. The only problem is that the beer is cloudy, even after 1 micron filtration...
It's on the carbonation now - we'll look at how it ends...
What I didn't mention in the recipe above is coriander
I'll post the beer photo after cold conditioning

 

[belgbrew]

Ok here's the final beer
Tastes really good

 

[hercher]

Looks good. It should improve with time (which will also help the clarity).