work in progress
--Kaiser 20:24, 26 December 2007 (CST)
When malt is crushed not only the endosperm is crushed, but also the husks which should remain intact as much as possible since they are needed as the filter bed for lautering. Depending on the tightness of the crush, enough of the husks generally remains intact to allow for smooth lautering. Besides impeding the run-off during the lauter, overly shredded husks can also contribute to astringent flavors. During the mashing process, tannins are extracted from the husks. This tannin extraction can get over the taste threshold if the pH is to high and/or the sparge water is to hot. But husk-dust can also cause excessive tannin extraction due to the significantly increased surface area of the husk material.
To alleviate lauter problems and/or astringent off-flavors, many commercial brewers either condition their malt before crushing or crush their malt wet (wet crushing). The latter is also done to reduce the O2 intake during milling and dough-in process in a modern low O2 brewhouse, but is fairly impractical for the home brewer as it requires milling grain that is already mixed with some of the mash water.
Malt conditioning can however be employed by the home brewer. But it is strongly recommended NOT to do this with mills in home brew stores due to the risk of making a mess. In order to condition malt, the moisture content of the malt is raised by about 2% [Narziss, 2005] with the use of low temperature steam or a very fine spay of water. 2% is a very small addition of water. For a 5kg (11lb) girst) this is only 100ml (3oz) of water. This moisture collects in the husks of the malt which become much more pliable as a result of this treatment. If to much water is used for the conditioning, it is not completely absorbed by the husks and will cause malt flour to stick to the roller of the mill. If this happens try to run some dry malt through the mill to clean it up.
To condition the malt put the malt in a bucket and use a spray bottle of water to spray the top of the malt a few times. Now mix the malt and repeat. You want to distribute the added moisture as evenly though the malt as possible. Soon the malt's feel with become less like dry straw and more like leather. Once it looses it's dry feeling and a few of the kernels start to stick to your hands let the malt sit for a few minutes to let the husks soak up the moisture. Get the mill ready and set it fairly tight. After all, you conditioned the malt to be able to crush it tighter. When you mill the malt you will notice that once in a while a crushed kernel will stick to a roller of the mill. This is ok and it only becomes a problem if a dough starts to build up on the rollers. In this case you used to much water. Run some dry malt through the mill to remove the dough.
After crushing a hand full, look at the crush. You want to see kernels that look more flattened (like oatmeal) than crushed. Pick them up and the endosperm should be dry and come out easily. If this is the case you can continue crushing the rest. If they still look more broken than flattened add more moisture and try again. In the beginning you may want to stay on the safe side and don't add to much water to avoid the risk of doughing-up the rollers.
When you mill conditioned grain it will not as easily flow from the hopper into the mill. If it starts to stall, agitate the hopper or use a stick to help it along. Do not use your fingers especially of the mill is motor driven.
Here are pictures to illustrate the difference between the crush of dry and a conditioned malt at the same setting of the mill (JSP Maltmill, 19mil/0.48mm)