High Attenuation In A Strong Scotch Ale

[MartinS]

In December, I brewed a Strong Scotch Ale. I mashed at 70-71, and did a 3 hour boil. Everything went perfectly on the day. I pitched a healthy 2L starter of WLP028 to the 1.090 wort. I've somehow ended up at a final gravity of 1.012. That's 87% apparent attenuation... with a 70 degree mash...

After about 2 weeks in primary, it had hit 1.034. Things had slowed down a lot, and a lots of yeast had dropped out. I decided to rack it off to keep it off the cake, as I figured it might take take a while to get through the last few points. Another 2 week passed, and it had stabilised at 1.030 (spot on what I was after!). There was still some evidence of slow fermentation. I was about to go on holidays for 3 weeks, so I racked again.

I took a measurement this morning, and it has dropped another 18 points! It doesn't taste infected, apart from a "hot" alcohol flavour (which I think is to be expected for a 10.2% beer).

I'm pretty careful with the sanitation of my fermenters: I clean with very hot nappy solution after use, then repeat when I want to use the fermenter again. I then let them soak in iodophor for about half an hour before drip drying.

Is there anything else that could have caused my high attenuation? Anything I can do to recover the beer?

 

[THE DRUNK ARAB]

With a mash at 70-71C I would be amazed that you could get that much attenuation with the WL 028.
Whitelabs state 70-75% attenuation I notice.

Is your mash thermometer reading true? That is where I would start anyway.

Also did you add any adjuncts to your grain bill such as brown sugar or the like? Lets see the grainbill as well.

What size yeast starter did you pitch?

C&B
TDA

Edit: Fat fingers

 

[MartinS]

With a mash at 70-71C I would be amazed that you could get that much attenuation with the WL 028.
Whitelabs state 70-75% attenuation I notice.

Is your mash thermometer reading true? That is where I would start anyway.

I'm pretty sure the thermometer is good. I have two glass thermometers that I test against each other from time to time, which are within a degree of each other. I give it a thorough stir at dough-in, then measure in a few different places with one of the thermometers.

Also did you add any adjuncts to your grain bill such as brown sugar or the like? Lets see the grainbill as well.

No adjuncts:
~90% JW Pale
~5% Carafoam
~5% Caramunich
and a touch of Roast Barley

What size yeast starter did you pitch?

Two litre stir-plate starter.

 

[MartinS]

Hmm.. The more I think about it, the more I think I must have somehow picked up a bug in the third fermenter:

It dropped 4 points in two weeks in the second (hitting right on my expected target), but 18 points in three weeks the the third... Seems a bit sus..