cookie chemistry: soft or crisp?

There are several things which affect whether cookies will be soft or crisp. Shirley Corriher, food chemist/writer/professional cook, illustrates how to make 3 different cookies from the same basic recipe: thin crisp, or soft puffy, or in between, by changing the type of flour, fat, sweetener, and liquid.

For thin crispies: use butter for the fat; use part sugar, part brown sugar, and a little corn syrup as the sweetener; use milk for liquid, and use bleached all purpose flour. Use baking soda.

For a puffy cookie, use shortening instead of butter (butter-flavored shortening works great), and use cake flour. Use an egg for liquid. Use all brown sugar for the sweetener. Use baking POWDER instead of baking soda.

For in between cookies, use half butter and half shortening; use mostly brown sugar with a touch of corn syrup; use cake flour; use an egg for the liquid. Use baking powder.

There's more to her cookie chemistry lesson, but her illustration of 3 different types of chocolate chip cookie hanging off one basic recipe shows you how many things are going on inside those little morsels. Proportions change slightly too - more liquid for more spread and crisper cookies, less sugar for less spread and softer cookies, more baking soda than a standard recipe for extra crispness. Kinda makes you want to go get a degree in food chemistry!