Dark Mild finished at 1.020?

“Mashed for an hour at 158.” Mashing at that high of a temperature will yield a wort with lots of unfermentables (e.g., dextrins).

In addition a significant portion of the grain bill is specialty malts (e.g., crystal malts,…).

Given the above it makes sense to me that the final gravity would not be low.

Cheers!

 

With your grain bill, mash length, mash time, yeast strain, and OG of 1.039, I get an FG prediction of 1.012 in BrewCipher. Slightly higher than what you saw in BC, maybe because you expected a slightly lower OG. Whenever you get an actual OG that's different from what you expect, you should apply the predicted attenuation % to the actual gravity...or tweak the mash efficiency parameter to get the observed OG and thus a new FG prediction.

Having said all that, you only got about 48% apparent attenuation, which is very low, given your recipe. So low that I would first suspect that there was a gravity measurement error. But it sounds like you took multiple measurements with multiple devices. That leaves two possible issues I can think of.

- Your mash temp may have been higher than 158F and may have caused premature unravelling of some enzymes, producing a less fermentable wort.

- Stuck/unfinished fermentation.

If you haven't packaged this yet, I'd recommend giving it some more time, in case the fermentation wasn't done. If you have, and particularly if you bottled, I'd proceed with caution.

 

My personal feeling is, you've tasted the beer and it's not too sweet for your taste. You're kegging, so there's no danger of bottle bombs. I would proceed to keg.

 

It's always a race between conversion and enzyme denaturing. But usually conversion wins.

A lot of people mash in this way. And although some enzymes may be sacrificed early on, those grains you're adding in the latter part of the mash-in also contain more enzymes. If your strike water was of the appropriate temperature to settle at the target mash temp, I doubt this was a problem.

I would probably just let it go for the two weeks and if gravity hasn't budged any further, keg it like @minderbender suggested. Since it already tastes good and you're not bottling, I'd say that's a good option. i.e. I wouldn't go to great lengths to try to fix something that's not really broken.

As an aside, I don't think I would ever worry too much about a fermentation that may not be completed after only eight days. Usually it would be, but stuff happens.

 

That's not beer, that's ~ 2.4% ABV colored water