Casein is not vegan!

Casein (from Latin caseus "cheese") is the most predominant phosphoprotein found in milk and cheese. When coagulated with rennet, casein is sometimes called paracasein. British terminology, on the other hand, uses the term caseinogen for the uncoagulated protein and casein for the coagulated protein. As it exists in milk, it is a salt of calcium. (Source: Wikipedia)