A-amylase, basically, liquifies starch turning it into carbohydrate soup. The enzyme breaks down the starch chain somewhat randomly, but at 1-4 links. Everytime it cuts the chain, a reducing end and a non-reducing end are formed. B-amylase will chop off two molecules from only the non-reducing end of the chain and combine the two molecules with one molecule of water, producing maltose. B-amylase, also, can chop off three molecules from the chain and combine with one molecule of water, producing maltriose. The more non reducing ends, the more b-amylase as to work on and the faster it works. Usually, to have conversion happen in ten minutes, the malt needs to have de-branching enzymes in it. The enzymes work with a and b amylase by producing a lot of non reducing ends. The problem is, the enzymes are kilned out of modern malt. It is not unusual for tri-decoction, using under modified malt, to convert in ten minutes. A small portion of the de-branching enzymes remain intact in low temp kilned malt. The decoction brewer, using under modified malt, will employ a rest at the temp favoring dextrinase and maltase. The iodine test is about the only thing a homebrewer can use as a conversion gauge. A way to do the test is to pour a table spoon or so of mash liquid into a plate and drop by drop add iodine to the puddle. Until a layer of iodine is formed. Check the color at the interface. If the color is deep red/brown at the interface, the sample contains gelatinized starch (amylose and large a-limit dextrins (not too good). If the color is light red, the sample contains simple a-limit dextrines. If the color is brown/violet it contains small a-limit dextrins. Absolutely, no color change indicates a good mix of a-limit dextrines (maltose and maltriose). After using iodine a bunch of times, gaining experience, you will be able to gauge what is in the sample by the colors. That is the method Siebel teaches. A drop of liquid into a drop of iodine, don't cut the mustard. Nor, does the chock method. If knowledge of what enzymes do and how they work is desired, Noonan's book on lager brewing is a good primer. The ASBC and ABJ have articles on the subject. Sometimes, there is more to brewing, than dumping hot water on grain. Single infusion allows a brewer to work with an extremely narrow pallette, when enzymatic action is considered. Check out recipes for programmed mashing and notice the various temps employed, that take advantage of enzymatic action. If desiring to move beyond infusion or program mashing, attempt tri-decoction, using low modified malt. You might be amazed at what can be produced. If a brewer is focused on two to three hour brew time, the processes aren't for that brewer.
