OK - I've always done session beers (everything was less than 1.060) so a "big" beer is new to me. I brewed up a 1.085 dopplebock. I pitched the slurry (WLP833) from a helles. I rinced the yeast slurry (1.5-2L) and pitched it into a 1L starter on brewday to get it active. That fully active starter was pitched into the beer later in the day (at 47F) and was fermenting the next morning. It fermented vigorously for a number of days (at 50F) and slowed down after 4-5 days and was showing no bubbling in the airlock at 10 days. I took a gravity reading on the 10th day and it was down to 1.028-30. There is still a lot of yeast in the beer - very cloudy just no signs of active fermentation.
This is about 65% attenuation and that yeast should do about 75% attenuation.
Again, this big of a beer is new to me. Assuming I keep it at 50F for another 10-15 days should I expect to see this continue to slowly drop down to about 1.020? I've always seen my 1.055 beers ferment out (actively) in 5-6 days and basically stop there (where they were expected to finish) so my experience says that this is done.
So, a little help for a newb in the deep water of these high gravity beers.
Prost......