You know baking is all about science, but it’s all about control as well. When you use unsalted butter in a recipe, you can control the exact amount of salt in your baked good. When you use salted butter, you have no idea how much salt you’re using because it varies between each brand you see at the store. Chowhound tells us the exact amount of salt in popular brands and some are double the amount of others! And this doesn’t even include store-brand butter, so who the heck knows how much salt is hiding in those. The flavor in your baked good is completely compromised, especially if butter is the main flavor– think poundcake, sugar cookies, pie crust etc. It doesn’t matter as much in cooking since you can taste as you go, but it’s crucial to control the salt in baked recipes. Pair this with the added salt in your recipe and you’ll wind up with super salty poundcake.
Salt is a preservative and therefore, salted butter has a longer shelf life than unsalted butter. We’re talking 3-4 months of shelf time. For fresher butter, reach for the unsalted variety. (Or heck! Make your own!) However, some brands add “natural flavor” to unsalted butter, which extends its shelf life (not quite as long as salt). This is usually lactic acid, which also helps regulate its pH.