The McDonald's Shamrock Shake is back: What you never knew about the green-tinged treat

(NEXSTAR) – Being one of the few green things on the McDonald’s menu, it’s always a notable event when the Shamrock Shake makes its annual appearance.

The shake, made from vanilla soft serve and minty syrup, first debuted at U.S. McDonald's locations in 1970. But it was originally concocted several years before by Hal Rosen, a Connecticut franchisee who was looking for something to draw customers around St. Patrick’s Day in the mid- to late-'60s.

“He was ahead of his time,” Mark Rosen, his son, said of his father’s contributions to the McDonald’s menu in a 2000 article published in the Hartford Courant.

As the story goes, Rosen debuted his Shamrock Shake at a location in Enfield, Connecticut, before sharing the idea with other local franchises. Upon its national debut in 1970, it was “an instant success,” according to McDonald’s. Its sales are even credited with funding the very first Ronald McDonald House in 1974.

It’s unclear how the original recipe differed from today's, but early commercials for the treat appeared to indicate it was merely a vanilla shake with green coloring. (“They’re vanilla-flavored,” a voiceover states in an early commercial. Another ad reportedly published in 1973 describes the shake as having “McDonald’s great vanilla flavor” while “the green is just a favor.”) A few online reports further suggest the original incarnation was actually lemon-lime-flavored, though it’s possible that was just a regional variation, the Dallas Observer reported last year.

McDonald’s and Rosen’s son, however, maintain that it was minty from the moment it was conceived. (A representative for McDonald’s was not immediately available to comment on why some older advertisements billed it as a “vanilla-flavored” treat.)

Most of the early surviving campaigns only added to the confusion: Old commercials shared to YouTube conspicuously avoid specifying the shake’s flavor, pushing it as a springtime treat because of its green coloring. Shamrock Shakes were also promoted in campaigns featuring McDonaldland character Grimace and his Irish-accented Uncle O’Grimacey — and both were satisfied simply by the shake’s “beautiful green” shade.

Later commercials more openly advertised the shake’s minty flavor. (In the early ‘80s, McDonald’s even pushed a Shamrock Sundae featuring green minty syrup.) And today, McDonald’s is still touting the periodic popularity of its mint-flavored shake — now often sold alongside the relatively new Oreo Shamrock McFlurry.

“Make your friends green with envy and snag one of these famously minty treats while supplies last,” McDonald’s wrote in a recent press release.

Both green items, of course, are only on the menu for a limited time beginning Feb. 5. (Pickles and lettuce, meanwhile, are green and readily available at McDonald's year-round, for anyone who may be interested.)