Belgian Dubbel final gravity

[bionut]

A few weeks ago i brewed a belgian Dubbel from some ingredients i had left.
6.5 kg Pilsner
0.1 kg Melanoiden
0.2 kg Wheat, flaked
0.02 kg Chocolate malt
0.5 kg Dark candy syrup (180ebc)
0.3 kg Sugar Molasses (raw cane sugar, unrefined)

The OG was 1.064 on my setup and i fermented it with WLP530 Abbey Ale yeast. Now the gravity is 1.020 for two weeks. It feels a little high for me, around 70% attentuation, while the yeast have a potential of 75-80% attenuation.
I under pitched a little to encurage the yeast to give aromas, can this be the problem? Or is something normal for this grain bill and i can bottle it?

 

[Build]

What temperature was your mash? What temperature did you ferment at, was it constant? With your grain bill/yeast you should be able to go to 1.010 or less with no problem.

 

[Denny]

Forget the attenuation rating of the yeast. Attenuation depends a lot more on wort composition. Using the same yeast, I can get from 60-85% depending on the wort. Did you make a starter? How big? Otherwise, what Build said.

 

[ACbrewer]

What temps did you ferment at? Typically Belgians start in the 65's and then go up on the last day or 2

 

[bionut]

The mash temperature was quite high, i over shooted it a bit, around 68°C. I fermentent at around 20°C and rise it to around 25°C.

 

[ACbrewer]

Mash temp could be it. There are several temps that are important for making malt out of the grains, and if you miss, you will under produce the malt (I'm explaining that wrong). Although 68degC is 154.4 degF which is very close to perfect iirc. Which I probably don't.
Basically there is long starches and one protein breaks them down to small starches, but it is active round 145F ~63C and is destroyed as the temp goes up (and doesn't work below a certain temp). Then another rest usually takes place higher up to break the small starches down to sugars like maltose. Depending on the grain, you can skip the first rest around 145. But if you were to high on your mash, it may have made it so all the enzymes that break down those starches were destroyed before they did the temp breakdown. This would leave more residual material to be in the finished beer.

 

[EarthwormJim]

Are you using a hydrometer or refratometer for your reading? Once alcohol is present it will throw off the reading on a refractometer. There are calculators online to correct the reading if that is the case. Hydrometer will be ok though.

 

[Denny]

Mash temp could be it. There are several temps that are important for making malt out of the grains, and if you miss, you will under produce the malt (I'm explaining that wrong). Although 68degC is 154.4 degF which is very close to perfect iirc. Which I probably don't.
Basically there is long starches and one protein breaks them down to small starches, but it is active round 145F ~63C and is destroyed as the temp goes up (and doesn't work below a certain temp). Then another rest usually takes place higher up to break the small starches down to sugars like maltose. Depending on the grain, you can skip the first rest around 145. But if you were to high on your mash, it may have made it so all the enzymes that break down those starches were destroyed before they did the temp breakdown. This would leave more residual material to be in the finished beer.

You'd have to be well over 165F for that to happen. Also, most malt these days has such high diastatic power that mash temp makes a lot less difference than it used to.

 

[bionut]

I use a hidrometer which i tested in water and it is calibrated. The beer is now in bottles, will see if i made bombs or not.
LE: a friend made the exact recipe so we can meet and compare the two. His fermented to 1.018, so it may be the grain bill or the sugars...

 

[ACbrewer]

You'd have to be well over 165F for that to happen. Also, most malt these days has such high diastatic power that mash temp makes a lot less difference than it used to.

Thanks. I'd forgotten the exact numbers. It was why the OP's "68C (155F)" didn't seem high to me, but he said it was so I went with that.