Certain dairy foods contain fumaric acid to help stabilize them and to add tartness. Chocolate milk and eggnog, for example, often contain fumaric acid, which helps enhance their flavor. Some types of fruit-flavored drinkable yogurts also contain fumaric acid, according to the Food and Agriculture Organization of the United Nations. Cheese, milk powder, cream powder, liquid whey, whey cheeses, dairy spreads and cream soups might also have fumaric acid added to them.