I routinely take my pre-boil gravity after sparging to determine mash efficiency so that I can throw in DME or Dextrose for a lower than expected yield or add water for a higher than expected yield, all in an attempt to hit my target OG.
I batch sparge, and recently I realized that the force of circulation when collecting 2nd and 3rd runnings is not enough to fully distribute the collected sugar in the entirety of the wort.
When brewing today, I took a gravity reading directly after sparging, and then again after stirring for a solid minute. The pre-stir reading when cooled to 60F was 1.080. The post-stir reading reading when cooled to 60F was 1.050, so stirring definitely had an effect.
Unfortunately, with a pre-boil gravity of 1.050 compared to the projected yield of my grain bill, I would have achieved a mash efficiency of 96%. While this high of a yield would be great, it is not possible. I should be in the ballpark of 78-80%.
My thoughts are that either (A) I did not stir long enough and vigorously enough or (B) temperature variations in collected wort are preventing consistent absorption of the sugar throughout the wort.
It seems the best time may be just before boil when the wort's temperature is consistent and the process of heating has moved things around a bit.
Has anyone experimented with this and found the optimal time/process?