21. Although many varieties of cake can be made, they may all be put
into two general classes: _sponge cake_ and _butter cake_. These classes
may also be regarded as cake made without butter and cake made with
butter, for it is the presence or absence of fat in a cake mixture that
makes the difference in the method of mixing the ingredients and
determines the texture after baking. While there are many true examples
of each of these classes, it must be remembered that there are also
numerous variations of the two which must be placed in either one or the
other of these classes. For instance, a true sponge cake does not
contain baking powder, but some recipes for sponge cake are given in
which baking powder is included. Such recipes must be regarded as
variations of sponge cake, for they are more similar to that than to
butter cake.
The ingredients are not, however, the only source of difference between
these two general classes of cakes. They also differ as to the method
used to combine the ingredients, the correct oven temperature for
baking, and the length of time required for the baking. All these
differences must be thoroughly understood if successful cake making is
to be the result.