The first thing a brewer needs to do before getting to work making beer is to ensure that their brewing grain is ready to go. Assuming they aren’t malting their own barley, this means milling, or crushing, the grains. This crucially important step can make or break a beer before it has even begun. The key is to crush the grains enough so that it exposes the starchy center of the barley seed without damaging the grain hulls that encase them. If the crush is too course, not enough of the starch will be converted to fermentable sugars. If the crush is too fine, the husks, which act as a filter bed for the brew will be destroyed, and the brew will become gummy and unusable.
Below is a picture of well-milled barley. Note how the barley kernels have been cracked into large pieces while the hulls have remained largely intact.
Beer Brewing is science,but also artical!