Fifty years is a long time. It’s half a century. It’s the average life span of a chimpanzee. It’s enough time to create one (1) Mariah Carey (maybe?). And as of this year, it’s also how long people have been ordering Shamrock Shakes at McDonald’s.

Every March since 1970 — along with St. Patrick’s Day, possibly corrupt college basketball tournaments, and the opportunity to misquote Julius Caesar — the seasonal tradition has returned to McDonald's. Despite not being the fast-food chain's best-known (or, arguably, best) limited-time product, it’s garnered a cult following over the years. So in honor of its golden anniversary at the Golden Arches (and our collective slow march toward death), let’s take a look at its backstory, which is surprisingly rich for a novelty fast-food beverage.

A green-tinted tradition born in the ’70s

The Shamrock Shake, as manufactured by McDonald's, is a pale neon green milkshake, served with whipped cream. It comes in three sizes ranging from small (460 calories and 13 grams of fat) to large (790 calories and 22 grams of fat).

The Shamrock Shake is only available seasonally, typically arriving on the McDonald's menu sometime in February and remaining there at least through St. Patrick's Day (March 17), generally disappearing again in mid- to late March. After debuting in 1970 and returning annually for the next two decades, it was briefly discontinued in the 1990s but brought back in the 2000s due to customer demand. In 2012 it was made available at every McDonald's nationwide, but it's currently a regional offering in the US. It’s also available at some stores in Canada and Ireland.

In 1980, McDonald's also introduced the Shamrock Sundae, a vanilla sundae drizzled with disconcertingly green syrup, but due to low sales it was discontinued after a year. Now it's mostly relegated to awesomely '80s commercials like this one:

What flavor is the Shamrock Shake?

This might seem obvious — it's mint, right? — but Googling the query turns up quite a few debates on the matter. Some people claim it has a hint of lime, others say it's as minty as toothpaste, and still others think it's just a vanilla shake dyed green. Turns out these have all been correct at various points in history: At least one account says the original recipe contained lemon-lime sherbet; the formula was changed in 1973 to be just vanilla with food coloring. Not until 1983 did the shake become the mildly minty confection we know today.

Per the McDonald’s website, the shake’s three components are vanilla reduced-fat ice cream, “Shamrock Shake syrup,” and whipped light cream. It probably would not surprise you to know that all of these ingredients contain various forms of high-fructose corn syrup.

In 2017, McDonald’s experimented with several chocolate Shamrock shake versions, including a Shamrock chocolate-chip frappe, a Shamrock hot chocolate, and a Shamrock mocha — plus a special straw specifically designed for the shakes. This year, the chain is offering the OG shake plus an Oreo Shamrock McFlurry, in case your utensil of choice is spoon rather than straw.

The history of the Shamrock Shake is more detailed than you'd expect for a fast-food novelty beverage

When McDonald's introduced the shake in 1970, it was called the St. Patrick's Day Shake; it received its new, catchier name a few years later. The Shamrock Shake is also partially responsible for creating the network of Ronald McDonald House Charities, which provide housing and other services to sick children and their families.

In early 1974, the daughter of Philadelphia Eagles tight end Fred Hill was undergoing treatment for leukemia, and Hill and his wife, Fran, were spending most of their time in the hospital. They wanted to find a housing solution for other families like them, so Hill turned to his teammates to help fundraise for alternate accommodations.

Eagles general manager Jim Murray had the idea to harness the power of McDonald's advertising; through a friend at the company's ad agency, Don Tuckerman, Murray learned that the next McD's promotion would be to add the Shamrock Shake to the menu for St. Patrick's Day. Murray worked with McDonald's founder Ray Kroc and regional manager Ed Rensi to organize a week-long promotion wherein all proceeds from Shamrock Shake sales would be donated to the Eagles' fundraising efforts.

They raised enough money to buy a seven-bedroom house near the hospital, which in 1974 became the first Ronald McDonald House. The nonprofit network has since expanded to include 357 houses in multiple countries.

Though Shamrock Shake sales no longer benefit the nonprofit network, the two have been linked in recent publicity stunts — like this one from 2010, in which a 24-foot shake was dumped into the Chicago River in honor of a McDonald's donation to build a new Ronald McDonald House in the city.

This year, McDonald’s is doing a splashy fundraiser for the charity: Per CNN, it’s auctioning off an 18-karat gold, gem-encrusted Shamrock Shake cup supposedly appraised at $90,000, with all proceeds going to Ronald McDonald House.

According to the eBay auction page, the cup, which is sized to fit around the plastic container your garden-variety Shamrock Shake is served in, is adorned with “50 green emeralds and white diamonds — representing 50 years of Shamrock Shake flavor and delicious whipped topping. There are 50 yellow diamonds in each of the Golden Arches for 50 years of being a fan fave at McDonald’s.”

As of the morning of February 28, the cup was going for $32,100 with 52 bids; if you happen to have tens of thousands of spare dollars lying around and want to get in on the action, the auction is open until March 6.

The secret to the shake’s popularity: artificial scarcity

More than 60 million Shamrock Shakes have been sold since 1970, according to Fox News. David Zlotnick, senior director of global public relations for McDonald's, told Vox that it's "one of McDonald’s most popular seasonal menu items and has gained a cult-like following over the years," though he declined to provide any hard numbers. He also said the Shamrock Shake is most popular in Philadelphia, the birthplace of its "origin story," so to speak.

The primary driver of the shake's popularity is its "seasonality," a.k.a. limited availability. Not only is the drink only available for a short time each year, it's also not offered at every McDonald's, which has led to more than one journalist chronicling an ill-fated search for the shake.

The shake has even been the subject of a scandal or two. In 2010, Jimmy Fallon caused a Shamrock Shortage at the McDonald's in New York's Union Square when he bought 100 of the shakes to hand out to members of his Late Night audience after taping that evening's show. And in 2017, McDonald’s drew mockery and ire for a (since-deleted) Twitter video advertising its new chocolate Shamrock shake, featuring a man in a tartan hat with bagpipes sipping his beverage as Stonehenge appeared in the background. That the Shamrock Shake is not exactly a symbol of authentic Irish culture doesn’t lessen the ridiculousness of a fast-food chain using Scottish cultural signifiers and one of England’s most famous landmarks to hawk its tangentially St. Patrick’s Day–related novelty drink.

Controversy aside, the shake's cult fandom pales in comparison to that of the McRib, which is arguably the most well-known limited-time offering ever to grace a McDonald's menu. Many news outlets (including Vox) have tried to explain its meaty mystery. But this fascinatingly in-depth piece from the Awl's Willy Staley, though focused on determining whether the unpredictable emergence of the McRib is tied to the price of pork, sums up the psychology behind the sandwich as well as its fellow limited-time menu items, Shamrock Shakes included:

We’re marks, novelty-seeking marks, and McDonald’s knows it. Every conspiracy theorist only helps their bottom line. They know the sandwich’s elusiveness makes it interesting in a way that the rest of the fast food industry simply isn’t. It inspires brand engagement, even by those who do everything they can to not engage with the brand. I’m likely playing a part in a flowchart on a PowerPoint slide on McDonald’s Chief Digital Officer’s hard drive.

In other words, the Shamrock Shake is a classic example of the "art of artificial scarcity": By limiting the Shamrock Shake and McRib to certain times of the year, McDonald's ensures added interest and higher sales. (Plus, it gives us great Onion articles like this one.)

Don’t I remember a weird green mascot of some kind?

You're thinking of Uncle O'Grimacey. Blobby and bright green with an Irish accent, O'Grimacey was the uncle of Grimace, the big purple ... creature ... that frequently appeared in the McDonaldland series of TV commercials that McDonald's began airing in the early 1970s.

The web series Irate the 80's explains how O'Grimacey was introduced in the '70s and became the star of several McDonald's TV commercials and merchandise items before being phased out in the '80s. (If you fear clowns, beware: Ronald McDonald appears in this video.)

The actor who voiced Uncle O'Grimacey, Lennie Weinrib, also lent his voice to numerous cartoon characters including Scooby-Doo's nephew Scrappy-Doo, Bigmouth from The Smurfs, and Gomez Addams from the animated Addams Family series.

I’m only reading this to find out where to get a Shamrock Shake

Well, hey, you made it almost all the way to the end! You can order a shake via the McDonald’s app; there’s also a separate finder app available on Google Play. Or you could just make your own — the internet is replete with recipes in every variation you can think of.

And while making your own might require a little more effort than just pulling up to the McDonald’s drive-thru, a homemade version is almost guaranteed to have less high-fructose corn syrup. Plus (and perhaps more importantly), it can be made any time of the year you please, thus finally freeing you from the tyranny of artificial scarcity.