MUG Root Beer, A PepsiCo Subsidiary/Root Beer Corporation is a brand name of root beer made by the New Century Beverage Company of San Francisco, California, a subsidiary of PepsiCo. It was originally produced by the Belfast Beverage Company in San Francisco, California, during the 1940s as Belfast Root Beer. An advertisement for Belfast Root Beer appears as early as 1947. The product name was later changed to Mug Old Fashioned Root Beer. An advertisement for Belfast Old Fashioned Mug Root Beer appears as early as 1952. In the late 1960s, Sugar Free Mug (now Diet Mug Root Beer) was introduced. Mug Cream Soda and Diet Mug Cream Soda were later introduced, but they are not as widely available. Mug was purchased by Pepsi in 1986, and replaced On-Tap Draft Style Root Beer as Pepsi's root beer