But nearly all root beers went through a major trauma in the 1960s, when the Food and Drug Administration banned any sassafras extract that contained the suspected carcinogen safrole, a colorless essential oil. Safrole had been the flavoring most closely associated with root beer, and bottlers scrambled to find substitutes, including an artificial flavor to replace the prohibited extract. Wintergreen is now the dominant flavoring in most root beer, along with vanilla, which supplies creaminess.
Formulas vary, however.
Some root beers include oil of anise, adding a licorice taste. Cinnamon, lemon oil, orange oil and cloves also are used. An extract of the yucca plant supplies foaminess. Some boutique brewers, such as Virgil's, are again using sassafras extract, but in a safened-up version. There's no definition of what a root beer should be.