The science of cookies vs cakes

Thanks so much for your help, everyone! I have a mother who makes delicious baked goods but uses the same technique for all of them. I grew up thinking the science didn't matter, but I now realize the recipes she makes over & over are the ones that work with her technique. As I explore new recipes, I'm having fun experimenting. I love that cookies are more flexible, because so many different results can still taste good, but I'm very interested in learning the science as well. It's fun.

It's not cookies vs. cakes. It is science, though, and it involves flour and water and leaveners and time and technique and. . .

To see for yourself how one tiny little tweak can make a giant difference in a cookie, mix up a batch of Toll House cookie dough exactly as the recipe directs. Bake cookies from half the dough; cover the rest of the dough and refrigerate it for at least six hours. Bring the dough to room temperature and bake the remainder of the cookies. The cookies made from the never-chilled dough will be somewhat flatter and will have a teeny bit more spread than the cookies made from the chilled dough. Oddly, the chilling has nothing to do with this effect, which is due to the length of time you've given the flour to absorb moisture from the eggs and butter; you've also given enough time to allow any strands of gluten to relax, and the cookies grow up and not out.

Icebox cookies, the homemade slice-and-bake kind, take advantage of this bit of science. The cookies don't have to be chilled--you could add an additional 1/4 cup of flour to the dough, then slice and bake them right away, but they'd come out a little harder than they're meant to be.

The same principle works for muffins, pancake batter and cakes, too. (For most muffins--if they don't contain frozen blueberries--and cakes, pour or spread or scoop the batter into prepared pans, but don't bake them for half an hour. For pancakes, leave the batter on the counter for 20 minutes before scooping onto a griddle.)

Letting flour absorb moisture is just one way to cause a variation between my cookie and yours. The differences multiply exponentially when you factor in specifics such as ingredient proportions and the addition (or not) of a leavener (or two), or techniques such as using a mixer to cream the butter and sugar or using a wooden spoon to stir melted butter into sugar.

To answer your questions: No, cookies are not less-finicky science-wise than cakes, and yes, they are so varied that they require different directions.

Am I as careful with cookie directions as I am with cake directions? If I'm experimenting and trying to make someone else's recipe my own, no. . .I'll do what I think it takes to get a cookie I like more than the original. However, if I want a cookie to turn out a specific way, I follow directions to the letter. To make my point, this is the example I always use because it's such a universal experience: Have you ever made or eaten a Nestle Toll House cookie where the chocolate chips are poking through very flat and crispy dough? That's what happens when the butter and sugars are not creamed together as the recipe directs. (But they still taste good, don't they?)

I think the reason cakes seem less forgiving is that everyone wants a light and moist cake, so the formula for getting that cake just right is quite specific. For cookies, there are many desirable outcomes depending on the kind of cookie you want - chewy, crunchy, cake-like, fluffy, huge, thin, lots of options. So, the adjustments in the recipe, baking time and temperature, all affect the type of cookie.

Cookies:
I've found cookies in general to be more forgiving than cakes. It all depends on how picky you are about your texture, though. Cookie recipes vary greatly, but so do those textures. All that being the case, if you mis-measure your flour in a cookie recipe, you'll end up with just as much of a mess as if you mis-measure it in a cake recipe. Beating eggs one at a time into a cookie recipe will usually result in higher, cakier cookies. But most cookies won't fail on you if you toss everything in together and stir.

Cakes:
Classic cake recipes (I'm not talking flourless cakes here) are geared towards getting the consistent texture that people expect from cake. You can toss everything in together and mix, but you have to be prepared for it to turn out denser and heavier than if you beat the eggs in one at a time. Cake ratios should be followed strictly if you want your end result to be like a bakery cake.

For cake you are essentially looking for a small range of variation with the outcome - you don't want a chewy cake for example. Cookies are more varied - some chewy, some crispy, some cake-like, etc... You don't have to be as careful with cookies because there is more range for an acceptable outcome. If you are looking for certain qualities you can tinker with the recipe. Here's some info from Cook's Illustrated:

By adjusting key ingredients, you can change the texture of any cookie recipe.
If you want chewy cookies, add melted butter. Butter is 20 percent water. Melting helps water in butter mix with flour to form gluten.
If you want thin, candy-like cookies, add more sugar. Sugar becomes fluid in the oven and helps cookies spread.
If you want cakey cookies, add more eggs. Yolks make cookies rich, and whites cause cookies to puff and dry out.
If you want an open, coarse crumb and craggy top, add baking soda. Baking soda reacts quickly with acidic ingredients (such as brown sugar) to create lots of gas bubbles.
If you want a fine, tight crumb and smooth top, add baking powder. Baking powder works slowly and allows for an even rise.