Fading chocolate flavor in a stout

[LovesIPA]

I brewed a stout a few weeks ago and it's been on tap since 8/28. When I first kegged it, it had a slightly harsh up-front bitterness which faded quickly and left an absolutely delicious chocolate finish. If you've ever had a Boulder Chocolate Shake Porter, the finish reminded me of that. What I was hoping for was that the bitterness would become more palatable and the chocolate flavors would stay. The good news is that, after a couple weeks in the keg, the bitterness isn't harsh and the beer is quite good. One of the better batches I've made, actually. Everyone who tries it likes it and comes back for more. But those delicious chocolate flavors have faded into the background so much that I can barely tell they're still there.

Here's the recipe (5 gallon batch):

6.5 lbs Maris Otter
1.5 lbs white wheat
1 lb flaked oats
12 oz roasted barley
10 oz Crystal 80
8 oz black patent

Mashed at 156 for an hour. I added the roasted barley and the black patent at the end of the mash, stirred it up good, then set the grain bed and sparged.

1 oz Chinook pellets (11.1%) at 60 min

OG was 1.060. FG was ~1.018. Hydro sample was impossible to read in the sample vessel but it's +/- 0.002. ABV 5.8%.

How can I retain those chocolate notes? Do I just have to secondary with cacao nibs if I want a moderate to strong chocolate flavor?

 

[giraffe]

A few percentage points of medium roast malts would help, like in the brown malt to chocolate malt range. As will a touch of residual sweetness, from a lower attenuating yeast, or other method will help the perception of chocolate.

 

[LovesIPA]

Forgot to mention that I fermented at about 63 with a package of rehydrated S-04.