Milling is done to better allow the mashing liquor to access the centre of the barley. It is important that the grain husk remain intact, as the husks are used to form a filter bed during lautering. At the end of milling, the brewer should be left with a range of fragments of barley, but no whole grains, and largely intact husks.
There should be little flour, as this leads to haze in the final beer and is poorly retained by the husk bed in the lautering process. It is also important that most of the endosperm is broken up, leading to better conversion of the starch to sugars. We supply large diameter smooth rollers running at different speeds in our brewery system. Smaller grain mills can be made with slotted or knurled rollers and the mill gap must be set wider to avoid crushing the husks.
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