Ridiculously high attenuation

I brewed an English Barleywine a little over 2 weeks ago. I had an OG of 1.097, which was right on the money (thanks to my brand new refractometer). I just took my initial sample post-ferment, and I ended up with a gravity of 1.017, giving me an attenuation of around 83%. Usually, this wouldn't be an issue, but I used WLP002 (London ale yeast), which is supposed to be between 63-70%. I'm concerned that this is going to turn out much drier than I wanted it to be. What could I have done to have this active of a ferment?

I did make a good, healthy 2.5L starter for it. Fermentation temps never got above 68. I'm baffled.

P.S. I did drink the hydrometer jar. It tastes pretty good thus far, but there's a noticeable hotness to it from the alcohol. Will aging mellow out the alcohol flavor, or is it something I'll just have to deal with?

Thanks!
Beard

 

What was your mash temp?

 

It came out a little HIGHER than I expected. I mashed between 157-155. Started at 157, ended at 155. I was aiming for 152, but I decided to leave it at 157 because I like a big mouth feel for most of my beers more than I like the simple sugars I would've gotten from lower temps.

 

did you add much sugar? if not, sounds like you might need to calibrate your thermometer

 

And or hydrometer. Something is a miss.

 

Did you calibrate your refractometer with distilled water first? What was your grain bill?

 

Oops didn't see it was a refractometer, you do know that they aren't really accurate for measuring alcohol, just sugars. There's a conversion chart you need to use.

 

I took OG with a calibrated refractometer and hydrometer, FG with hydrometer. The numbers I got as my OG were within 2 points between the 2 tests, so I figured it was close enough. I did add a half a pound of molasses, but I don't think it would be enough to thin it out this much. I know something isn't quite right here, but I don't know what. My thermometer hasn't been calibrated in 3 batches, so that could be the issue, but I don't think it is. I had a good mash, and ended up with an 83% efficiency for the day (not too shabby). I honestly think it's just the yeast. I haven't worked with WLP002 before.

Here's the recipe:
16lb Mariss Otter
1lb Crystal 60l
.5lb Blackstrap Molasses
1oz Nugget hops 15.2% AA (60 min)
2.5l Starter for WLP002 (london ale yeast)

Process:
(BIAB) Mashed for 90 mins @ 157-155F, batch sparged @ 169F.
Boiled 2 hours, 1 hour no hops, 1 hour 1 oz nugget in hop sock.
Wort chiller used until temp hit 65F, siphoned to carboy, aerated via shaking, and pitched my starter.

 

That 1/2 pound of molasses might be enough to bring that attenuation up, I'm pretty sure it is close to 100% fermentable.