December is the time of year when many participate in cookie swaps, bring tins of cookies to a neighbor or friend and leave a plate out for Santa. Some people like their oatmeal cookies crispy. Some prefer a chewy chocolate chip. Still others want something more cake-like, like a black and white cookie.
How can you turn great-grandma's recipe for chewy into crispy?
Science!
"Cookies are actually really complicated," said Jeff Potter, the author of "Cooking for Geeks: Real Science, Great Hacks and Good Food," according to Live Science. "They're a whole microcosm. Every single thing in food science that happens pretty much happens in cookies."
Cookie basic ingredients are flour, water, fat and sugar. When flour is mixed with water, a protein called gluten forms. It's a long molecule that helps trap air bubbles that form in rising doughs, like bread dough, according to Live Science. Too much gluten makes cookies tough, but too little leaves you with cookie puddles spreading out and baking on your sheet as one big cookie blob.
The highest gluten percentage is found in bread flour - 15 percent - compared to 7 percent (by volume) in cake flour, according to Live Science. All-purpose flour is mid-range and OK to use for cookies, but some bakers like using cake flour for cookies too.
So, if water encourages the production of gluten from flour, what keeps it in check?
The balancing act is completed by fat and sucrose (regular table sugar).
Butter is 80 percent fat and 20 percent water while shortening is all fat. Since water makes more gluten, what would you use for cake-like cookies?
Butter.
Cookies made with shortening do not increase the cookie's gluten, so if you don't want cake-like cookies, use shortening.
But this is where butter gets complicated. Butter is an emulsion, according to Live Science, so the water is held captive by the fat in butter. In order to get the water from the butter to mingle with the flour, you need to melt the butter and break some of the water/fat bonds.
Now, let's talk the sweet stuff.
White sugar consists of molecules of sucrose. Corn syrup is mostly glucose and the molecules are about half the size of sucrose molecules, according to Live Science.
"There are actually more molecules of glucose in a cup (of corn syrup) than there are molecules of sucrose (in table sugar), because glucose is a smaller molecule," Potter said, according to Live Science. Using corn syrup as the sweetener will keep more moisture in your cookies. Brown sugar is a mix of molasses and white sugar, and the combination of glucose and fructose will keep the moisture levels of your bakes goods high, according to Live Science. If your cookie has less than 6 percent moisture, you'll have a crispy cookie.
How do you prefer your cookies? Crispy, chewy or cake-like?
