Cookies are a microcosm of baking, in which the chemistry of each ingredient has a huge effect on the finished cookie. You make many decisions when deciding on a cookie recipe: which kind of flour, which fat, which sweetener, which leavener, whether to add liquid. Your choices determine if the cookie will be flat and crisp or soft and puffy, pale gold or deep brown.
Flour affects color, texture, and spread
Higher protein flours, such as bread or unbleached flour, can create more of the strong elastic gluten that makes cookies chewy. If cookies are too crumbly, use bread flour and sprinkle it with a little water (to form gluten) before combining the flour with other ingredients. Cake flour and bleached all-purpose flour have lower protein levels. If you prefer a tender cookie, rather than a chewy one, choose one of these flours and mix the fat, sugar, and flour before you add any liquid. The amount of protein in flour affects browning. The more protein in the flour, the browner the cookies. Cookies made with unbleached all-purpose or bread flour will be browner than those made with bleached all-purpose or cake flour. Low-protein cake flour is acidic, which reduces browning even more.
Higher protein flours absorb more liquid, so cookies will spread slightly less than those made from the same recipe with lower protein flours. If your recipe uses cake flour and an egg, however, you’ll get less spread because the acidic flour makes the egg set fast.
Protein levels also affect a cookie’s height. Lower protein flours don’t absorb as much water as high-protein flours, so they make more steam, which puffs cookies more.
Change the chemistry, change the character
The walnut–chocolate chip cookies on the left (below) are puffy, soft, and pale
gold. We used:
cake flour (low protein, acid)/ more steam and puff; less browning
shortening (high melting point)/ less spread
all brown sugar (hygroscopic, acid)/ soft and moist; less spread when used with egg
egg /moisture for puff; less spread with acidic ingredients
For the thin, crisp cookies on the right, we used:
all-purpose flour (high protein)/ browning
butter (protein)/ more spread; browning
baking soda (alkali)/ browning
corn syrup (glucose)/ browning; crisp
white sugar (sucrose)/ crisp
no egg/ no puff; more spread
Sugar type influences browning and texture
Corn syrup is mainly glucose—a sugar with a structure that makes it brown at a lower temperature than granulated sugar (sucrose). Cookies made with corn syrup will be browner. Sweeteners can make a cookie crisp or soft. Cookies made with sugars that are high in sucrose (granulated sugar and maple syrup) or glucose (corn syrup) tend to stay crisp. Sweeteners high in fructose, such as honey, act differently. Fructose is hygroscopic (meaning it absorbs water from the air), so cookies made with a lot of honey get soft upon standing. Brown sugar is also more hygroscopic than granulated sugar. Brown sugar is also slightly acidic, so it can help limit spread in cookies using an egg.
Butter makes cookies spread more
Butter melts immediately in a hot oven, so cookies made with butter will spread. Also, butter is only about 80% fat, with about 18% water, which contributes to spread. Shortening, on the other hand, melts at a higher temperature, so cookies have more time to set in the oven and will stay domed.
The fat you use makes a small difference in how brown your cookies will be. Since protein promotes browning, cookies made with shortening (which has no protein) will be slightly less brown than those made with butter (which has a little protein).
Leavenings affect color more than rise
Your choice of baking powder or baking soda influences color but rarely leavening. Baking powder contains baking soda and enough acid to neutralize the soda and doesn’t influence the color of cookies. But baking soda by itself is alkaline and is a major contributor to browning. In most recipes, 1 teaspoon of baking powder or 1/4 teaspoon of baking soda will leaven 1 cup of flour. When the leavening is much over this, the bubbles get big, rise to the surface, and pop, and there goes your leavening. In most cookie recipes, the amount of soda is excessive for leavening and is used primarily for color.
More liquid means more spread, unless you use an egg. Many cookie recipes have no liquid per se but depend on the water in the butter (about 18%) to make enough gluten to hold the cookies together. Other recipes may use 1 or 2 tablespoons of liquid or an egg. The amount and type of liquid can influence the spread and puff of cookies.
Usually the more liquid (if it isn’t an egg), the more the spread. When an egg contributes the liquid, there’s little tendency to spread. This is particularly true if there’s an acidic ingredient (such as brown sugar, cake flour, or chocolate), which makes the egg set quickly to limit spread. A bit of extra liquid, or the liquid from an egg, turns to steam and can make cookies puff more.