One theory about the beginnings of peanut butter points to a St. Louis physician who, in 1890, ground up peanuts to serve as a nutritious and easily digestible food for his elderly patients. However, earlier evidence of the existence of peanut butter can be found in South American and Asian cooking, and in African cooking in the United States. A note in an 1883 Savannah newspaper suggests that peanut butter was already a Georgian favorite.
However, it wasn't until around 1890 that the peanut butter boom in the United States began. By 1900 grocers were selling it by the pound in big tubs, stirring the oil that rose to the top. In the 1920s, sweeteners and hydrogenated fats were added to peanut butter. (Hydrogenated fat is a combination of hydrogen and unsaturated oil. This produces a solid fat and prevents oil separation.)
To meet current United States Food and Drug Administration standards, peanut butter must contain 90 percent peanuts and have none of the following additives: artificial flavoring or sweetener, preservative, or coloring. It also must have no added vitamins.
Sources: Chalmers, Irena. Great American Food Almanac, p. 154; Garrison, Webb. How It Started, pp. 27-28; Harris, Harry. Good Old-Fashioned Yankee Ingenuity, pp. 219-20.