The below image is a high definition picture to provide detail of a good crush size that removes the grain husk while leaving it intact, and cracks the grain open without pulverizing it. The husks are useful for keeping the grain bed from compressing, and a lot of grain powder will become gummy, plugging the gaps in the grain bed and preventing water/wort from properly draining through. This crush was obtained with a single pass through a 0.045"/1.1mm roller gap on a three roller mill.
Other tips for increasing efficiency (and avoiding a stuck mash) include:
- not adding the grain too fast when mashing in (which then requires excessive mechanical agitation); if grain is added slowly in a circular motion it has time to sink naturally and might not need much if any mixing to remove air pockets
- adding toasted or dark malts after the pale malts to keep them near the top of the grain bed (they tend to fragment more when crushing and will be more gummy),
- not overmixing the grain when mashing in (mix just enough to remove air pockets;
- not moving the Mash Mixer near the false bottom on the Colander as this can force grain into the bottom (perforations or wedge wire) and plug it up,
- not starting a recirculating pump until at least 10 minutes after mashing in (allowing time for the malt to absorb moisture and expand); start the pump with the return valve closed and slowly open so as to not pump too quickly (if grain is in the line, the valve can be opened wide if necessary for a very short period to past the grain through)
Controlling vorlauf and lauter rates for best efficiency and preventing a stuck mash
How to build your own malt mill
