I am very allergic to casein and even a small amount will make me very out of breath. If I have it in a liquid form, which is not cooked, I will have a reaction in 15 to 30 min. If I have it in a cooked form, such as a cake, cookie, or bread, I will not have a reaction until the next day, usually 15 to 20 hours. It must have something to do with the cooking of it that makes me have such a delayed reaction. It was very confusing when I was trying to figure out what was wrong with me. Debbie Jones