An update! Quoting myself just for reference...
I ended up bottling this after about 2.5 weeks in secondary. There was a layer of obvious peanut oil scum at the top during this time. Also, as time went on, a fine tan substance began to accumulate just below the top layer of scum (what I referred to as "buoyant yeast" in another post). I now believe that this was just very fine peanut scum/oils slowly coming out of suspension. As many have said before, the PB2 leaves a HUGE layer of trub at the bottom. My initial batch was just over 6 gallons, and I ended up with
The beer sat in bottles for 3 weeks before I tried one, which was about a week ago. Over this time, another layer of the fine tan substance began to accumulate at the tops of most bottles. A quick shake sends it back into suspension, and I'm pretty sure it's not bacteria. The beer is otherwise very clear. Head retention has been interesting, with results varying widely based on how/into what I pour the beer. Sometimes the head is disappears almost immediately, having behavior that resembles the head on Pepsi. Other times, when I do a particularly vigorous pour, it comes out like this:
...and hangs around for a good 20-count. I did my best to rack under the oil at the top, but this behavior, combined with the tan scum presence and a slightly non-uniform color to the head, makes me believe that even more extended settling time in secondary is necessary if head retention is a priority. Personally, I'm not too disappointed.
Mouthfeel was surprising: not as thick or full-bodied as I expected. The first bottle I had almost reminded me of pop, while later ones have seemed heavier. Despite the lactose and cara-pils, it's not nearly as creamy as I expected from a full-on stout, but is noticeably heavier than the brown ale that I brewed a few months ago.
Finally, flavor. There's a heinous amount going on in this beer, as expected. The aroma is very nutty, though more like "cooked peanuts" than "fresly-opened jar of nuts". The chocolate comes through on the aroma, as well, but isn't as well-defined. Any hop aromas are fleeting. Up-front taste is sweetness from the lactose and malt. Then comes a very flabby chocolate flavor, and immediately after comes the peanut flavor. They really run together, and I'm a bit disappointed by the lack of flavor definition. However, the finish is all peanuts. Like with the aroma, you can tell the nuts have been cooked. For anyone wanting to brew this, let me be clear: It does NOT taste like a Reese's peanut butter cup. The flavor isn't as sharp, more like chocolate peanut butter ice cream, and the flavors are darker and gentler. Any hop flavors really need to be hunted for.
If I were to do this again, I would make a few changes. First, I'd drop the chocolate, or perhaps use extract instead of cocoa. The flavor isn't really defined, and just gets in the way. Hand-in-hand with this, I would reduce the amount of lactose. Also, I might take some of the PB2 that was added during the boil and add it to the quantity which was steeped in vodka and put into secondary. This will probably add more "tan oil scum" to the final result, but it's obvious that some of the peanut flavor was subdued by cooking during the boil.
Verdict: 3 jars of PB2 in the boil + 1 jar&vodka in secondary WILL get you a nice peanut aroma and flavor in your beer. It's not a "fresh peanuts" flavor, and it's not a "Reese's peanut butter" flavor, but it is distinctly peanutty and is pretty delicious.