Dear Jason,

In the old days when root beer was ROOT BEER, there was some intrinsic quality of the brew that gave it a rich foam. Actually, that was why it was called root beer rather than root ale or root cider, neither of which are as foamy (I am told) as beer. However, in the days of real root beer there was still a variation in the degrees of foaminess. A BOWEY’S root beer sign from the 1930's promoted its product as being "solid" or "creamy", as opposed to foamy or frothy.

However, the key to the early root beer flavor, sassafras root bark, was banned by the FDA in 1960, as it was found that a chemical compound called safrole, the principal component of sassafras, was a weak hepatic carcinogen, which causes cancer of the liver. Thus, since then root beer has been artificially flavored, just like all the other soft drinks, and the manufacturers can make it with any degree of foaminess that they want to.

But back to the original question, regardless of its history, why is root beer so foamy? Since the manufacturers won’t tell us and since we have no ready means of experimentation, we will have to do as the early Greeks did. The Greek scientists, who developed much of the base of our modern reasoning process, were above experimentation. Such menial tasks were left to the slaves. They used pure logic.

The ancient Greeks were very good reasoners, but not always correct. For instance, they deduced that men had more teeth than women since men’s heads were generally larger. To actually count the teeth was beneath them. So let’s do a little reasoning. The first element of foaminess is carbonation. No CO₂, no foam. Therefore, the more CO₂, the more foam. However, increasing the CO₂ content would also make the drink more pungent (some people would say that it would have more of a ‘bite’.) So, undoubtedly, since root beer is not generally more pungent than many other soft drinks, the carbon dioxide content alone would probably not account for the foaminess.

Another factor that would be involved would be the viscosity of the liquid. As the viscosity of the soft drink is increased, the bubbles constituting the foam would have more of a tendency to form and to remain. (One doesn’t get much foam on a glass of carbonated water.) A third condition would be the surface tension of the liquid. As surface tension is increased the bubbles would have greater strength and a tendency to remain longer. So, the manufacturers of today’s root beer undoubtedly play with the degree of carbonation, viscosity and surface tension in their artificially flavored concoction to produce just the degree of foaminess that they want to market. The only unfortunate aspect of the whole thing is that the artificial flavors for root beer have never been a match for the real thing.