Developed in 1890 and promoted as a health food at the 1904 St. Louis World's Fair, peanut butter is a blend of ground shelled peanuts, vegetable oil (often hydrogenated) and usually a small amount of salt. Some contain sugar and additives to improve creaminess and prevent the oil from separating. Natural peanut butter uses only peanuts and oil, usually peanut oil. Peanut butter is sold in two forms — smooth or chunky, which contains bits of peanut. It can be easily made at home in a blender or food processor. Natural peanut butter must be refrigerated after opening and can be stored in this manner up to 6 months. Most other commercial peanut butters can be stored at room temperature for up to 6 months. Peanut butter is high in fat and contains fair amounts of iron, niacin and protein. See also peanut.