When a recipe calls for unsalted butter, as most (and nearly all baking) recipes do, how important is it to stick to the script? In other words, what's the harm in using salted butter in place of unsalted if that's all you have on hand? As it turns out, substituting one for the other is not such a simple swap.
Salted butter is great for spreading on toast, tossing with steamed potatoes, or melting and pouring over a bowl of popcorn. But in baking, every ingredient matters—even more than in other types of cooking. It's a chemical process, after all, and the properties of each and every component bear consideration. Here, we explain why.
Salt acts as a preservative, so salted butter has a longer shelf life than unsalted options. That means if you are looking for the freshest butter, unsalted is likely the better choice. You may not taste it on the tongue, but lots of cooks insist that you can taste the difference in freshness when the butter interacts with other ingredients in the finished dish.
The sodium levels in a stick of salted butter vary by brand, surprisingly more than you might think. By taking that variable factor out of a baking recipe and calling instead for unsalted butter, you retain control of the outcome. According to Sarah Carey, editorial director of food and entertaining at Martha Stewart Living, "Because most baking recipes are developed using unsalted butter, substituting the salted variety can be a bit of a challenge. How much salt IS in a tablespoon of salted butter? How to you adjust for it? It's kind of impossible to know. It's not the worst thing, but you might end up with a finished product that is slightly different than the original."
Salted butter contains more water than unsalted. Tests have found the water amount to range anywhere from 10 to 18 percent, depending on the brand. Butter with a low water content is preferable for baking, because extra water can compromise the chemical process that causes gluten to form, which will in turn affect the formation of the proper texture and crumb of your baked good. And because it's impossible to know exactly how much water may be in your butter (the amount is not listed on the label), it's best to stick to unsalted, for accuracy. You may not notice the discrepancy on your morning toast, but it will definitely alter the outcome of a cookie, cake, or especially, flaky pastry.
The bottom line is to heed the recipe's recommendations and stick to the butter that's listed. Trust that the recipe developers have done the testing—and the tasting—for you, and that the specific type of butter and amount of salt are included for very good reasons. Finally, it's worth nothing that there are instances when baking recipes are developed specifically with salted butter in mind. A few of my favorites are brown butter shortbread, developed using Kerrygold's salted butter and the classic ring-shaped Danish butter cookies. Both recipes rely on just a few ingredients, and are ultimately designed to let the distinctive taste of salted butter shine.