Getting the Wort Out (Lautering)
A Good Crush Means Good Lautering
There is a trade-off between particle size and extraction efficiency when mashing crushed grain. Fine particles are more readily converted by the enzymes and yield a better extraction. However, if all the grain were finely ground you would end up with porridge which could not be lautered. Coarse particles allow for good fluid flow and lautering but are not converted as well by the enzymes. A good crush has a range of particle sizes that allows for a compromise between extraction and lautering.
A good crush is essential for getting the best mash efficiency and extraction. There are two basic kinds of grain mill commercially available today. The Corona corn mill uses two counter-rotating disks to grind the malt. This often results in finely ground flour and shredded husks, which is not good for lautering purposes. Setting the crush too fine often leads to stuck sparges. This type of grain mill can produce a good crush without too much husk damage if the spacing is set properly (.035-.042 inch). It is the least expensive kind of grain mill, usually selling at about $50.00.
The other type of grain mill crushes the malt between two rollers like a clothes wringer. There is much less damage to the husks this way which helps keep the grainbed from compacting during the sparge. The two roller mill is more expensive than the Corona mill, about $100-150.00, but will give a better, more consistent crush to the grain with less husk damage. Examples of this type of mill are the MaltMill - Jack Schmidling Productions, Marengo, IL, the Valley Mill - Valley Brewing Equipment, Ottawa, ON, and the Brewtek Mill - Brewer's Resource, Camarillo, CA.
There is also a single roller mill which uses one roller against a fixed plate to crush the grain. It is called the PhilMill - Listermann Mfg. Inc, Cincinnati, OH, and also produces a good crush, like the two roller mills. It sells for about $80.00.
The insoluble grain husks are important for a good lauter. The grainbed forms its own filter from the husk and grain material. The husks prevent the grainbed from completely settling and allow water to flow through the bed, extracting the sugar. It is important to keep the grainbed fully saturated with water so it doesn't get compacted and impermeable. The wort is drawn out through the bottom of the bed by means of a false bottom or manifold which has openings that allow the wort to be drawn off, but prevent the grain from being sucked in as well. Usually these openings are narrow slots, or holes up to an eighth of an inch in diameter.