Ever since I built my own grain mill, I’ve been seeking out the fabled “perfect crush,” that ideal mix of whole, intact husk and fully accessible endosperm to promote maximum mash conversion while avoiding slow or stuck sparges.
I mill at a very fine gap of 25 mils (0.026″, or approximately 0.625mm) using a high-torgue, low RPM gearmotor; my grains are usually conditioned with a few ounces of water prior to milling. The usual result is the spent grains in my mash tun have a noticeable flour-like appearance. If my (batch) sparge is proceeding at a slow pace, this is usually what I expect to see after all is said and done:
However, despite using the same settings for milling the grist, occasionally the spent grain bed will have virtually no flour on top:
I’ve yet to identify the culprit. Possible considerations include: grain conditioning,* mill gap, mill speed (rpm), sparge temperature, sparge volume, lautering speed; or perhaps a combination, or perhaps some variables I haven’t considered. More on this to come.
* More information is available on the topic of grain (or malt) conditioning at Kai Troister’s wiki site, braukaiser.com