Butter also contains water and milk solids. In the U.S. butter is graded by letter code according to flavor, color, texture, aroma and body. AA, A, and B are the letter codes used. Grade AA will give you maximum results in your baking because of its sweet aroma and flavor as well as its smooth creamy texture.
Butter comes in two forms salted and unsalted.
Salt is added to butter for flavor and as a preservative so it will have a longer shelf life. However, salt can overpower the sweet flavor of the butter and can also mask any odors. Salted butter also contains higher water content. Also, the amount of salt added to salted butter varies from manufacturer to manufacturer and it is hard to know how much extra salt to add to your recipe. Unsalted butter has a short shelf life because it contains no preservatives.