Wyeast 1968 attenuation range. How accurate is it?

[kiwipen]

How accurate is the attenuation range that the yeast manufacturers provide?

I have a beer brewed with Wyeast 1968 that was kegged with approximately 4 grams of sugar per liter, and stored warm. (Approximately 4 G/L because the beer was split evenly on two kegs, and the sugar was mixed with water and boiled in a small pot and poured as evenly as I could between the two kegs.)

At the time the attenuation was 72,2%
Now it has fermented further, and the attenuation at the moment is 77,7%

Wyeast states that the attenuation range is 67-71.

OG: 1076
SG on day 10: 1020
FG after 13 days in the fermenter: 1020

New FG after 3 weeks: 1016

Could this be the yeast eating more of the sugar, or is it most likely something else eating away?

 

[FermentedCulture]

Although I haven't used it yet (I've got some ready in my fridge and Fuller's bottles) I've read a bit about this yeast.

There are a lot of threads saying it is prone to over-carbonation in the bottle, this observation includes people who have harvested from the bottle.

I'm guessing it utilises maltotriose slowly. Maybe there's an unknown about this yeast like it secretes something when the cells die in the bottle or maybe the simple sugars help stimulate using up the rest of the maltotriose? I wonder if the least flocculant cells are in the beer when bottled, so they stay in suspension for longer and use up more sugar than they would if they went dormant earlier.

Fuller's says that it changed behaviour to a bottom fermenting strain when they changed to CCVs.

 

[brewcat]

I don't really pay attention to their ranges. My attenuation is consistently higher.

 

[flars]

Attenuation ranges given by a manufacturer are developed by using the same standard wort for all the yeasts that are offered. The actual attenuation depends upon the fermentability of your wort.

 

[ESBrewer]

I think it has flocculated before the fermentation was finished and this slows things down so that it appeared as if fermentation had ceased. It is a known behaviour for this yeast (floc before ready) and White Labs advices to rouse it a bit. When the yeast is transferred, it is also easy to get some extra cells from the cake back to solution to help with fermentation, despite the fact that the cake appears solid. Just speculating.. And yes, attenuation ranges are just estimates, each wort will be different.

 

[HollywoodTK]

I use this yeast all the time, and on the first pitch I usually get 72-75% AA. After harvesting and pitching usually over target rates, I'll get 75%-80% consistently. I've repitched the same harvested strain 4 times and AA stays fairly stable at that range.

I have heard people having issues with stalling, but I have never had any trouble. I ferment generally at 64-66F for three days and then ramp up naturally to 68-70F for about a week or so until I cold crash and fine.