Fat Fat provides richness, moistness, and
suppleness. When it melts during cooking, it
lubricates the solid particles of flour and
sugar and encourages the cookie to spread and
thin — a quality that is sometimes desirable,
sometimes not. Because butter melts at a
lower temperature than margarine or
shortening, it gives cookies more time to
spread before the protein and starch set.
Butter is about 15% water, and is the main or
only source of moisture in such low-egg
recipes as shortbread and tea cookies.
Leavening Leavening, whether tiny bubbles
of air or of carbon dioxide, helps tenderize
cookies, and encourages them to puff. Many
cookies are leavened only with air bubbles
incorporated when the sugar is creamed with
the fat, or beaten with the eggs. Some are
supplemented with chemical leavenings.
Alkaline baking soda may be used when the
dough includes such acid ingredients as