What equipment are you using?
I had some initial trouble going to BIAB but I’ve picked up some lessons along the way.
You do need a finer crush with BIAB. Blichman recommends a “credit card” width between the grain mill rollers. If you’re using a drill to power the mill, SLOW the speed down or you’ll send bunches of uncrushed grain through. I will double crush some larger batches.
Use rice hulls if you have any wheat, rye or if you have a large mash bill. The mash may not be draining or flowing well enough to get a good extraction. It needs to drain well. As you mash, the temperature will vary in the mash bed, after discussing with Blichmann, I lift the malt pipe & bag out, let it drain back into the all in one for about 30-60 seconds, reseat, stir up the grains and get them fully immersed, resume recirculation. I find the temperature can drop on the Anvil about 3 degrees, so the mash is probably a bit cooler than this. I do this every 12-15 minutes.
I monitor with a refractometer like this :
https://www.amazon.com/Refractomete...=refractometer&sprefix=refract,aps,138&sr=8-3
This is within 0.003 of my 2 Tilts.
I typically mash for 75-90 minutes to meet my targets on bigger beers.
do you mash out? vourlauf? sparge?
if not, these can help your extraction efficiency. Without the sparge, I found that a 10.5 Anvil with a typical 5 gallon recipe I would ned about 1# more base malt to make my targets.
Doing a mash out, lift the malt basket & vourlauf and then sparge, I typically can do a 6 gallon batch or very close to 6 gallons with the same mash bill.
And as
@Brew Cat suggested, the bigger the beer, the more efficiency you’ll lose in a smaller kettle - the 10 gallon class units. I use an Anvil 18 for mostly 5-6 gallon batches, and sparge using a 10 gallon electric kettle. I can get into the 1.070’s easily with this setup where the 10 gallon was more of a challenge.
