We've been quite busy in the brewery in the last few weeks and posting a wee blog has been somewhat overlooked, so I'll try to remedy this with a few words and pictures on malt. More specifically on milling malt for brewing in our infusion mash tun..
When we grind the whole grains of malted barley in our mills, we're looking to unlock the soluble starch inside the husk so that our hot liquor (brewing water) can wet thoroughly the starchy granules in the mash tun. Here the the starch dissolves into the liquor and the malt enzymes, encased in the aleurone layer of the malt grain, then are able to start working their magic in turning the starch into sugars. Their work, in cleaving the long polysaccharide molecule chains into shorter sugar molecule chains, changes the indeterminate porridgy mash, or 'mash goods' into a distinct and discrete sweet wort and grain husk mixture, with the grain husks floating on top of the crystal clear sugary wort, or into the 'wort and grain bed'.
If the malt has been milled or crushed too finely, there is a tendency for the grain husks not to float on the wort, but to sink down and cause trouble and lengthy delays in the wort run-off to the copper - the dreaded 'stuck mash' and getting clogged up on the mash tun filter plates, where the wort is strained through slotted or perforated stainless steel plates, leaving the grain husks or spent grain or draff to be augured out for cattle feed. Another problem with too fine a grind, is that the malt husks contain much tannins, which can cause excessive astringency in the beer, if the husk is broken up too much.
Too rough a grind, with the grain husks hardly scuffed, will not expose enough of the white starch to the hot liquor, resulting in poor extract and a lower gravity of wort from the mash.