So I've been doing AG batches for about 10-12 times now. I was doing a brew last weekend and using my refractometer to check the brix (similar to Plato or SG) during sparging runoff. I've recently gone from 67% efficiency to 89% (per Promash).
The primary thing that changed was my mill. I had been using the local hobby shop mill with the belief they had it properly adjusted. Upon using my maltmill for the first time, I could easily see the grains looked extremely different than what I was used to. I found my sparge was MUCH slower due to dramatically slower drainage. I believe the Mill at my local hobbyshop has just been overused, and not adjusted regularly as it should and this is the biggest difference. I am very anal about temps during mash and sparge. I'm also very anal about water PH. Anyway, I'm getting off topic.
So, my observation was this. I kept checking my brix near the end of my runoff last 2 gallons. The ball valve on my mashtun was open all the way and the grain was regulating the runoff. Well it started to runoff twice as fast and my brix dropped from 6 to 3 almost immediately. I closed the ball valve to get just a trickle again, and retested my brix 4 more times and it came back to 5.5 again, then went back up to 6 and remanined that number for another gallon. It dropped down to five, four, 4.5, 4, 3.5, and so on, until I stopped it at 3.
My point is, that by dramatically slowing the sparge drainage I was able to get about 2-3 more gallons of wort. Due to the slower grain bed drainage (finder crush), and regulating my sparge (90 min) runoff I have made a dramatic increase in my efficiency. I'm now recomending my friends who don't want to mill grains at my house to at least mill them twice at the hobby shop. I even mentioned the issue at the hobby shop and they didn't seem too interested in the issue. I guess they get to sell 20% more grain that way....
Anyway, has anyone else ever noticed the fluctuating numbers during sparge speed? Does everyone else take 90 minutes to runoff? before the finer crush grains the best I could do on runoff is about 35-45 minutes at best....
Anywho, hopefully you all have some insight or find this information interesting.