I cranked down on the gap in my mill a little at a time over the course of several batches, watching my efficiency go up with each adjustment. My current gap setting is .029" (.737mm) on the narrow end of the mill and .055" (1.40mm) on the wide end of the mill. (My mill only adjusts on one end.) The rollers are somewhat smooth with fine ridges that run the length of each which adds to the severity of the crush.
If you are relying on your homebrew store to crush the grain you order, ask if they will narrow the gap, or if not, to mill the grain twice. They should be accommodating but only after they warn you about a stuck sparge. Smile and nod politely.
"Oh, but what about a stuck sparge?" I hear you say.
Not to worry my little friend, I solved that problem awhile back when I switched from using a false bottom to a short length of braided hose. Go here if you're interested in that easy project. But, even if you choose to keep using the traditional false bottom, a minor adjustment to achieve a finer crush will probably increase your efficiency without causing any problems. There is a lot of emphasis on 'cracked but not crushed' milling in the homebrewing literature but I think there is a lot of leeway to that old saying. Have no fear.
|Flaked wheat on left and a severe crush of malt on right|
Secondly, I fly sparge for a good 45 minutes for a ten gallon batch. This is where I'm getting an additional 5% + efficiency in my process. From my personal experience, this continuous rinsing for an extended period will achieve greater results than the batch sparge method. I also make sure that I calculate the amount of sparge water so that when I reach 13 gallons of wort, my mash tun has run dry. In other words, except for the water absorbed by the grain, I leave no residual water behind at the end of the sparge. For me this means assuming I will loose half my mash liquor to the grain absorption and will off-set that loss with additional water in the hot liquor tank. On a side note, I don't mess with the mash once I finish the vorlauf and start the sparge. I've witness some brewers stirring the mash (trying to increase efficiency I suppose), especially batch sparge brewers and for the life of me I can't understand this abusive behavior.
Finally, (regarding the fly sparge method) to set my mind at ease, I will occasionally check the gravity of the final running of my sparge to assure that I am not falling down below 1.008-1.010 range and judging from the taste of my beers, I can tell that there is no tannin extraction happening.
So, be brave and give your grains that extra little nudge to provide you with a better efficiency which leads to savings when it comes to grain purchases.