Usefulness of SG reading on first, second, third runnings in batch sparge
I now have 3 batch sparged all grain brews under my belt. All were for 5 gallons of beer. Here is brief summary of my methods:
-All calculations in Beersmith2
-Add strike water from HLT via march pump to MLT (Large coleman xtreme cooler, maybe too large for 5 gallons)
-Stir in grain, and let sit for 5 minutes
-Take temp to see if I meet strike temp, if not add boiling water from stove
-Continue to monitor temp for 60, adding boiling water if dropping below 145F
-Voulauf by recirculating wort in MLT via march pump until clear
-Lauter 1st runnings into Boil Kettle via pump
-First batch sparge, stir, vorlauf, and lauter into BK via pump
-Second batch sparge, stir, vorlouf, and lauter into BK via pump
Over the course of these 3 brew sessions I've been trying to dial in on my equipment variables for use with Beersmith2. VOLUMES were my biggest problem, especially since it took me 3 batches to get my strike temperature and mash temp high enough and stable for 60 minutes (needed to add boiling water more than I wanted).
My third brew session was on point. My question now: what is the usefulness of taking an SG reading on the first, second, and third runnings? I understand that they should be decreasing in SG, but how can I use these numbers on the fly to benefit my brewing? I've been monitoring these numbers somewhat, but I don't quite understand how I can "use" them in the moment of brewing.
I'm also taking the pre-boil gravity after ALL runnings are in the BK. At least with this number I have an estimated number from Beersmith to compare, and I can add water or boil longer in the BK to compensate.