If you have a way to mash the oats, and then maybe steep the other grains, and then combine that into the kettle, then I think it could work.
I've never done a true BIAB mash, but you may be able to get a big BIAB bag and mash 8 pounds of grain in the kettle and then sparge up to your desired boil volume, and then add the extract at flame out. If you could do that, that would be my preference I think!
Would it look like this? I've got some bulk LME I bought to do a couple 15 minute Pale Ales. I was thinking I could do a 10 gallon extract batch in my BIAB setup if I did partial mash. So for 5 gallons (half the batch to keep the math simple) of that recipe, I'd have:
Partial Mash
4 lbs LME
4 lbs Pale Malt, Maris Otter (3.0 SRM) Grain 63.64 %
1 lbs Oats, Flaked (1.0 SRM) Grain 9.09 %
12.0 oz Victory Malt (25.0 SRM) Grain 6.82 %
10.0 oz Chocolate malt (pale) (200.0 SRM) Grain 5.68 %
8.0 oz Barley, Flaked (1.7 SRM) Grain 4.55 %
8.0 oz Black Barley (Stout) (500.0 SRM) Grain 4.55 %
8.0 oz Caramel/Crystal Malt - 80L (80.0 SRM) Grain 4.55 %
2.0 oz Chocolate Malt (450.0 SRM) Grain 1.14 %
2.00 oz Williamette [4.80 %] (60 min) Hops 31.6 IBU
1 Pkgs British Ale II (Wyeast Labs #1335)
If I am doubling that, I will have 16 lbs of grain, for a 10 gallon batch. Will I be able to mash that in a Bayou Classic 11 gallon pot? I have found that 15 lbs of grain was already pushing the limit with the basket in the pot. Although I also was using 9 gallons of water to mash (15 lbs/9 gallons water for a 5 gallon batch). How much water do I need to convert all of those grains?
I suspect that if I can limit the amount of water I use, I will be able to mash all of it in the pot. I can add more LME if efficiency is a concern. I am trying to use up the rest of that bulk LME.
Thanks.