Lillian Stone discussed the differences between root beer and sarsaparilla for The Takeout. The key distinction is where each drink comes from:
There’s a great scene in The Big Lebowski when Sam Elliott’s character inexplicably asks a bowling alley bartender, “You got a good sarsaparilla?” It’s an old-timey request, although it feels natural coming from Elliott’s brilliantly mustachioed mouth. The bartender passes him something that looks a lot like root beer—but isn’t. Ready for your cowboy lesson of the day? Here goes: While modern sarsaparilla and root beer have similar properties, they have very different origins.
Sarsaparilla has a rich history beyond hokey westerns and touristy roadside saloons. It was originally derived from the zarzaparrilla vine, which originated in parts of Central and South America.
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Today’s root beer is almost interchangeable with sarsaparilla, but it wasn’t always that way. Root beer was originally derived from the sassafras tree, a member of the laurel family which is native to North America and parts of Eastern Asia.
The operative words in root beer’s origin is “originally derived”. Apparently, the sassafras tree creates a potentially toxic byproduct called safrole, which the FDA banned and now root beer makers use different flavour additives instead.