Dusty Miller and the truth of the Grind

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.

Above you can see the sample port of our two-roller mill, showing a sample of the grist (past participle of grind) which has come through the mill, on its way to the grist case. The malt has not been ground like flour, not even like wholemeal or stoneground flour, as the husk sizes are far too big. The gap between the two rollers is 1.50 mm, which is sufficient to crack open the malt kernels, yet not break the husk up completely, so that we have plenty of big husk fragments, each having a bubble of air attached, which allow the grain bed, as we call the body of husks, to float successfully above the draining out wort.

Here is another shot of a sample of grist, just on a plain white background for contrast.Plenty of husk fragments, looking almost as if they had been cleft lengthways. The malt starch granules don't show up too well as they are white also! A perfect crush for an infusion mash tun.

 And here is the cone of grist inside the grist case from today's Blackfriar. The grist does look very pale, considering Blackfriar is quite a dark beer, but then the dark crystal and roasted malts only consist of about 7% of the grain bill.

That'll be getting mashed in at 6.30 tomorrow morning, so I'd better see if I have a bottle of Blackfriar in the cupboard to celebrate the brew with in the evening!
Slàinte,
Ken