is a member of the class of elements called halogens; other members include chlorine, bromine, and fluorine, all of which are more reactive. As a solution of potassium iodide, iodine is used to identify the presence of the amylose component of starch. The helical structure of amylose supplies a matrix within which iodine molecules can assemble, leading to the formation of a blue–black color. After the saccharification steps of the mash, brewers will perform an “iodine test,” where potassium iodide is added to a small mash sample. If the starches have converted to sugars, the blue–black color will not form; conversely, the presence of the color indicates that starches remain. In this case, the brewer may decide to extend the mash sequence or take other action.

The second major use of iodine in breweries is as a sanitizing agent. Iodophor, a concentrated liquid containing iodine complexed with surfactants and sometimes acids, is a highly effective sanitizer with limited toxicity and corrosive effects. When diluted to 12 to 15 ppm, it is often used as a “no-rinse” sanitizer, especially for fermentation vessels and other stainless-steel equipment.