I am planning to brew a dark patersbier. My thought is to take the recipe for a dubbel and scale it back to around og 1.040-45. Does that seem like a good plan, or is there something else I should think about when formulating the recipe?
I did something similar; basically imagined a patersbier that was brewed from the second runnings of a dubbel. I had some issues with my process, so I didn't get a very good result. But I think it's definitely worth trying. The small beer rule of thumb - mash high to get more flavor and character from less malt - definitely applies.
What grist and sugars are you looking at? You might want to slightly dial the % of sugar. E.g., if the dubbel uses 25% sugar, you might want to aim at 15% sugar and increase the malt proportion a bit. If your dubbel base has no dark malts, you might want to add some crystal in this case.
PS: I assume your dubbel base is something like 75% Pilsner and 25% dark candi syrup.
it should be in the 20% range for a patersbier. It is supposed to be dry and sessionable, and to me that means well attenuated with a crisp hop and malt character. Maybe look into using just d180 or sinamar to get you to the right color vs trying to do a partigyle. Maybe make a tripel, then for the patersbier 1/4 of the 2nd then all of the 3rd runnings to get you to the volume you want. As long as you don't run below what 1.008 on your run off. If not look at the 1.042-1.046 OG and use a sparge addition of roasted malts for a smoother dark wort.