Simple Test for Starch Conversion During the Mash
Simple Test for Starch Conversion During the Mash
One of the most critical aspects of whole grain brewing is determination of the completeness of your conversion of starch to simple sugars and this is critical if you are to provide the yeast with sugars they can metabolize. Grains contain sugars in long chains called starch and these chains must be broken into single molecules of sugar to be available to the yeast for fermentation. Failure to convert starch to sugars will mean failure to ferment completely. The result is more residual mouth-feel and sweetness than anticipated and lower alcohol content. The easiest way to test this process, and monitor its progress in real-time as the mash progresses, is called the iodine-starch test. Purchase a small bottle of Tincture of Iodine at a pharmacy (Kroger’s Pharmacy sold it for about $3-4 in the first-aid section). At the beginning of the mash and about every 15 min thereafter, mix the mash well and place one drop of the liquid wort (no solids) onto a white or clear glass dish. Add one drop of the iodine mixture (do not contaminate the applicator in the bottle with wort) and mix gently by tapping the plate. If starch is present it will form a distinct dark purple/black precipitate. This is very thick and black at the beginning and you will notice it rapidly disappear as the conversion to sugar progresses. Retain each test as you move around the plate during the mash and compare the starch content over time. Usually with well modified grains, this occurs in the first 15-30 min with a small amount of final conversion occurring in the last 30 min of a typical 60 min mash. However, using this assay you can monitor conversion and fix any conversion problems by lowering mash temperature to extend the life of the amylase enzymes causing this conversion (they are heat labile), slow conversion by raising the mash temperature a little or stop conversion by mash-out at 68oF+ to inactivate the enzymes if conversion has been too aggressive. The plate washes clean in tap water. Cheers, Curt.
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