Angel cake is a type of cake that became popular in the U.S. following the invention of the han-crank egg-beater in the 19th century. It may also have been called angel food cake as a contrast to chocolate Devil's food cake, but the two cakes are completely different in type. Because of its white color and airy lightness it was said to be the "food of the angels". The chocolate, butter layer cake appeared at the same general time period, as one of the many new American cakes made possible by the invention of baking powder. Angel food cake is a type of foam cake whereas the Devil's food cake is a type of butter cake. Angel food cake requires that the egg whites be whipped until they are stiff, and gently folded into the other ingredients. For this method of leavening to work well, it is useful to have flour that has been made of softer wheat. This — and the lack of fat — causes angel food cake to have a very light texture and taste. It has led some detractors to liken the taste of the cake, as well as its appearance, to cotton. Angel food cake should be cut with a serrated knife, as a solid blade tends to compress the cake rather than slice it. Forks, electric serrated knives, special tined cutters or a strong thread should be used instead.