Used to test starch conversion.
Tincture of iodine is used to test starch conversion for partial and all-grain brewing. Collect a teaspoon of wort in a light colored cup or bowl. Place one drop of iodine on the side and then tip your wort into the it. If it turns black, there are still unconverted starches and mashing should continue. If it turns red or light brown, conversion is complete and sparging can begin