We use iodine in this video to confirm that the starch in our mash has converted to fermentable sugars. Alpha amylase is the enzyme that does this wonderful work for us but it does it a 155 degrees F. We typically just follow the directions and have no way of knowing if all our hard work has paid off. This is one way to verify that your starches are now sugar and your yeast will thrive. When iodine comes in contact with starch it will turn black, scientist call this blue-black. If no starch is present it will remain its own color on solids and dissipate in liquids. It is an amazing test and can be done right in your own home.