Why is root beer the only carbonated soft drink that seems to retain its head indefinitely? Does root beer generate so much foam for the same reason that alcoholic beer does?
Traditionally, as its name implies, root beer was flavored by extracts from the roots and bark of plants, most commonly sassafras. The foam associated with root beer is linked inextricably to proteins in the product. According to Brendan Gaffney, senior research specialist at Pepsi-Cola, makers of Mug root beer; “Protein stretches in contact with surfaces such as water, air and other contact surfaces to form films under turbulent conditions (shaking, pouring, pressure, etc.) that produce foam bubbles.”
The same sassafras that traditionally provided the flavoring for root beer also tended to produce and preserve the foam (so did the birch in birch beer).
But about thirty years ago, the US Food and Drug Administration ruled that sassafras was a carcinogen, and soft-drink producers scrambled to find substitutes, natural and chemical. Anthony Meushaw, executive director of the Society of Soft Drink Technologists, said that when the FDA ruling was issued, some soft drink producers chose to shift to artificial flavorings but wanted to retain the distinctive “head” that has been responsible for many a foam mustache on children. So some companies chose to introduce artificial, chemical “foaming agents” that did not add to the taste of the drink – their sole purpose was to make sure that a head was formed and retained.
Many of the most popular root beers use natural foaming agents instead. For example, Pepsi’s Mug root beer includes yucca and quallia (a tree found in the Andes Mountains of Chile) extracts that are natural protein emulsions. But the slightly bitter taste of these plants is overpowered by the vanilla flavor in Mug: If it weren’t for the foaming properties of the proteins in these plants, they probably would not be included, according to Gaffney.
Root beer became popular in the 1840s, long before the invention of colas. Presumably, the “beer” in root beer derived from the carbonation and head of the soft drink, and from the fact that some of the ancestors of root beer contained alcohol. Beer takes advantage of the natural proteins in rice and barley to retain its head. As you pour beer (or root beer) into the glass, the “shock” stretches the proteins and forms a head. Barring artificial foaming agents, the more protein in a drink, the higher and longer the foam is likely to form. By this measurement, then, Guinness Stout must have as much protein as a filet mignon.
(Submitted by Bob Foreback of Ann Arbor, Michigan. Thanks also to Chuck Flagg of Houston, Texas, and Jim Wright of Cordele, Georgia.)