I recently started an imperial stout using brown sugar. I made some modifications to the midwest imperial stout recipe. I did a partial boil due to using an older electric stove and less than ideal sized brew kettle. Using brewtarget to plan this out, my recipe was this:
2 gal filtered water for boil
steeped:
8 oz chocolate malt
8 oz roasted barley
4 oz caramel 120L
boil:
6 lbs dark liquid extract
1 lbs dark brown sugar
1 oz Glacier @75 min (would have been another oz of northern brewer if i had bothered to double check what hops i was going to use before ordering)
3 oz Norther brewer @75 min
1 tsp Irish moss @15 min
5 tsp yeast nutrient @15 min
2 oz Willamette @2 min
late addition:
6 lbs amber liquid extract
1 lbs dark brown sugar
Once i was sure that the late additions were completely dissolved and mixed in i topped up to 5 gal in my primary with semi frozen filtered water which also brought everything down to (slightly high) pitching temp for me. I came out with an og of 1.113 (right on the head for brewtarget) and pitched a well rehydrated packet of safale s-04 and hoped that the sugar wouldn't just over power the yeast or something. It smelled awesome, somewhat like a caramel espresso or something like that. I drank the hydro sample and considered licking the brew kettle, but i had other places to be that night (11/20) so had to skip that.
By the next morning i heard a strange whistling coming from the closet. When i looked in i found the airlock whistling and spraying foam out with the lid of the alepail bowed out. I quickly fit it with a blowoff tube and my closet sounded like i was boiling water in there for the next 16 hours before it slowed enough to put the airlock back on. By the end of the 2nd day all airlock activity had stopped (which means nothing really i know).
I plan to check the sg this saturday and transfer to secondary while pitching the champagne yeast (as instructed by the origional midwest kit "to reach a drinkable attenuation"), and i'll definately be tasting it then to see how it's coming. Og 1.113, expected Fg 1.028, 11 abv, 50 ibu, 42.7 srm if all goes as planned.