Flaky piecrusts used to mean lard, or at least butter.
Solid fats are important in baking, as they separate sheets
of dough into thin, independent flakes.
Traditional solid fats are animal-derived saturated fats
such as lard and butter. Some vegetable fats such as
coconut and palm kernel oils are solid, but they are
more expensive than some liquid vegetable oils like corn oil,
cottonseed oil, or soybean oil. These oils come from
plants that are used for more than just the oil they provide,
making them more economical to grow than plants
grown only for their oil.
Saturated fats like the
in beef fat have higher melting points than the
unsaturated fats in vegetable oils like
Vegetable oils can be made into solids by converting some
of the double bonds in their molecules into single bonds.
This is done by adding hydrogen, and is called hydrogenation.
A catalyst such as platinum is used to convert one or more
double bonds to single bonds with an attached hydrogen.
Some of the double bonds are converted from the normal
cis orientation with both hydrogens on the same
side of the bond, to the trans orientation, with
a hydrogen on either side of the bond. Such fats are
called "trans" fats, and are implicated in cardiovascular
With the double bonds converted to single bonds, the molecules
can fold and twist more easily, and the fat is now a solid.
Shortening also contains pieces of fats, called
and diglycerides. These are emulsifying agents that
allow water and air to be whipped into
the shortening, and help to thicken it and make it gel.