Chocolate Rye is one of my new most favorite grains. You are right in the the roast is much more mild. But the flavor is also more intense. To me, you get a lot more smoother chocolate flavor and a lot less roasted bitterness. And you can add a lot.
In my regular chocolate rye stout, which was around 1.066 OG, I think I added 1.5# chocolate Rye and .75# 500lovi roasted barley. It turned out amazing.
Give it a try you won't be disappointed.
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