I just put my second AG batch into the primary, but I ran into an issue I need some help with.
When I did my first AG batch, I used water that was treated by a water softener (I know, I know...it was all I had at the time). My calculated efficiency came in at 75%, using grain points and pre-boil gravity formula. BeerSmith confirmed reading.
For my second batch I used a combination of water from a rural mountain property well and chlorinated city water. (I plan to profile PH, etc. at a later time)
After mash @ 153F and batch sparge @168F, I only had about 5 gallons of runnings...I think due to the difference in water profiles. I'm thinking the lack of minerals in the soft water for my first batch prevented the grain from hanging onto it...that's a different question.
To compensate for the additional 1.5 gallons of water I needed to reach 6.5 gallons, I ran more water back through my mash tun, over the grain until I had reached 6.5 pre-boil. I stirred the wort vigorously and took a gravity measurement, which came in at around 1.022.
Using the same efficiency formula used for my first batch, I show my mash efficiency for this batch super low at ~ 49%. I double checked in BeerSmith which reports ~ 47%.
Is it possible that the topping off of the additional 1.5 gallons diluted the water, giving me a false gravity reading, or is this more likely a water issue?