Iodine Tincture2% Tincture of iodine is used to test starch conversion for partial and all-grain brewing. Collect a spoonful of wort in a small cup or light-colored bowl. Put a drop of iodine on the side of the cup, then tip your wort into the iodine. If it turns black, there are still unconverted starches present and you need to continue your mash. If it turns red or light brown, starch conversion is complete and you can start sparging.
