All of the real extract and calorie approximations were reported to the homebrewing community by Fix (most of it is originally due to Balling). You might try Fix's books. His day job was as a mathematician.
The explanation of DMS removal from wort and beer in Principles of Brewing Science was pretty interesting.
If that isn't mathy enough for you, I would recommend getting access to the Journal of the ASBC and learning to read German.