After a lesson on starch, we tested for its presence in foods that we eat (cheese, rice, crackers, cucumber, potato, and flour). Iodine (brown color) will turn blue black when starch is present. Our biggest surprise?  The cheese turned dark blue. After checking the ingredients, we discovered that potato starch was added to the grated cheese. I researched why it was added and found that it is used to prevent clumping.