Do you ever just dump all the ingredients for a cake into a bowl and start mixing, even if the directions give specific instructions on when and how to add ingredients? If you do, you probably end up with a decent cake, but if you followed the directions exactly there's a chance you'd end up with an even better cake. Why? It all has to do with chemistry.
These are the scientific reasons behind some of the most common baking directions.
1. Adding eggs one at a time
When eggs are added one at at time as you're mixing ingredients for something you'll bake, it takes them less time to incorporate into the mixture, according to Cook's Illustrated. If you add the eggs all at once, it takes more time to incorporate them, and that may be longer than the batter should be mixed. You may end up with textures in your baked goods that aren't ideal, which you'll learn about below.
The chemistry behind it: Oil and water don't mix easily. The oil in the batter — whether it's butter or a cooking oil — has a difficult time emulsifying with the large amount of water in the egg. When you add eggs one at at time, the mixture has an easier time thickening and emulsifying.
2. Creaming butter and sugar
Sugar is a solid, so why isn't it added around the same time as flour in many recipes? It's usually added with the butter or oil — like in this pumpkin bread recipe — before the dry ingredients like flour, salt and spices. Creaming together the fat with the sugar until they are light and fluffy will help your baked item rise better while making it more tender and soft.
The chemistry behind it: The Local Palate explains the air that's incorporated when creaming together sugar and butter acts as a "mechanical leavener," helping the baked good rise — often in conjunction with a chemical leavener like baking soda or baking powder.
3. Baking powder vs. baking soda
Speaking of leavening, some recipes call for baking soda, some call for baking powder, and many recipes call for both. They sound similar, but they aren't interchangeable.
They both help your baked goods rise, but they are different. Baking soda is sodium bicarbonate with nothing added. Baking powder is sodium bicarbonate mixed with a powdered acid, usually cream of tartar. The addition of cream of tartar makes the two different but they can work in harmony, too.
The chemistry behind it: Baking soda needs to be mixed with something acidic for it to produce carbon dioxide, which is what helps baked goods rise. Baking powder does not need to be mixed with something acidic for it to work. Baking soda reacts immediately when it comes in contact with acid. Baking powder simply needs something liquid for it to react with and works more slowly than baking powder.
Sally's Baking Addiction explains the two are often combined in a recipe because the baked good needs more lift than baking soda alone can give it. Using baking soda alone can neutralize the acid in a food where you want the acid in ingredients to shine through, like the buttermilk and goat cheese in Honey and Goat Cheese Muffins.
4. Using soft, but not melted, butter
When a cookie recipe calls for soft, room temperature butter and all you have is cold butter in the refrigerator, the microwave seems like a good way to soften it up. However, most of the time, this method results in the butter at least partially melted — something you don't want. Using melted butter in the batter will result in flat cookies.
The chemistry behind it: Melted butter in the raw dough makes it wetter than colder butter, and the wetter butter will make the cookies spread out faster, according to NPR's The Salt. The melted butter will also create smaller and more holes as the air pockets in the butter convert to gas, making for a chewier cookie. Cold butter chunks will make for fluffy, cake-like cookies. Soft butter, which is usually room temperature, gives you cookies somewhere in between.
5. Avoid over-mixing
Does it matter if you mix your ingredients together longer than the directions suggest? Yes, it does. Over-mixed batter can give your cakes and cookies a texture that isn't very pleasant, and worse, can negatively affect their taste.
The science behind it: The gluten in flour "provides structure and binds mixtures together" when it comes in contact with liquid, according to Spoon University. The more it's stirred, the more it's activated, and the batter is bound together too much. The end result is dense, stringy cake and dry cookies.
How do you know how long to mix batter? Spoon University says to "keep an eye on the mixer, and as soon as the batter is uniform (aka it has little to no streaks of flour remaining), you're good to go."