Unsalted butter contains no added salt. Think of it as butter in its purest form. As a result, unsalted butter has a shorter shelf life than salted butter (and many cooks will also tell you that it has a fresher taste). In terms of flavor, unsalted butter has a more pronounced mellow sweetness than salted butter. It’s best used in baking, or in situations where straying from exact ingredient amounts can make or break a recipe.