It's 7-Eleven Day, which means free Slurpees for all. Here's what you need to know about America's favorite slush

It's July 11,  which can only mean one thing -- free Slurpees. Here's what you need to know about the beloved icy beverage.

(CNN)For many Americans, July 11 will proceed like any other summer day -- hot, sticky and Slurpee-less.

But for 7-Eleven worshippers, 7/11 is a celebration, a gift and the official harbinger of Slurpee Season.
Today's the day the convenience store chain offers a free small Slurpee to any customer who walks through its doors, no strings attached. The offer's good from 11 a.m. to 7 p.m.
But before you pledge allegiance to the Slurp, pay homage to its history. Here's everything you need to know about America's favorite slush.

    A Slurpee is a sugary brain freeze in a cup

    The Slurpee is an icy, sugar-soaked brain freeze customers have been sucking down since the 1960s. It comes in standard flavors like Coke, cherry and blue raspberry plus whatever odd mix-and-match combinations customers can dream up. Some of them are distressingly neon in hue, and yes, a few sips may dye your tongue to match.
    To achieve that "uniquely Slurpee" slush, Slurpee machines are equipped with a compact refrigeration system that combines syrup, carbon dioxide and water under pressure in a freezing chamber. They're served at a crisp 28 degrees, 7-Eleven director of proprietary beverages Jacob Barnes told CNN in an email.

    The first Slurpee wasn't called a Slurpee at all

    Believe it or not, the original Slurpee isn't indigenous to 7-Eleven, though it was created under a different (but familiar) name.
    The way the Kansas Historical Society tells it, Kansas businessman Omar Knedlik bought a humble Dairy Queen franchise in the early '50s. His store didn't have a soda foundation, so he'd keep bottles of cola cool in the freezer. Customers went crazy for the frosty-bubbly combo.
    7-Eleven sold ICEEs first. They rebranded the slushies as Slurpees in 1967.
    In 1958, with an air conditioner ripped from the dashboard of a car, Knedlik built a machine that would freeze carbonated soft drinks and dispense them in a sippable form. And thus, the modern ICEE was born.
    7-Eleven wanted in on the brain freeze business and licensed their own ICEE machine from Knedlik in 1965. People loved them, and by 1967, ICEE machines were installed in every 7-Eleven location across the country, Barnes said.

    You can probably guess the origins of its name

    It's named for the sound it makes when you sip it through the straw. Or at least that's what it sounded like when a 7-Eleven adman thought of the name during a brainstorm session in 1967.
    The company wanted to rebrand the ICEE with an original name, and thus the Slurpee was born. ICEEs are still sold at movie theaters, theme parks and random spots in between, but 7-Eleven is still the only spot sippers can score a Slurpee.

    The original flavor is still the most popular

    Like the very first Slurpee ever served, Barnes said the Coke Classic flavor reigns supreme in Slurpee sales. It's trailed closely by cherry, but Slurpers beware -- it'll leave a red-tinted ring around your lips.

    Teens made the Slurpee popular

    Slurpees broke big once Americans started taking road trips around the US via the newly constructed interstate highway system in the post-war era, Johnson said. And rather than explore mom-and-pops along the way, road trippers wanted consistency when it came to food. That's when franchises like 7-Eleven and Dairy Queen took off, food historian Sarah Wassberg Johnson told CNN.
    But to cement the Slurpee's place in the cultural canon, its creators knew they had to cater to the demographic that would make it cool -- the youths.
    Top 40 radio DJs heavily pushed the product on their morning shows with success, Johnson said. 7-Eleven licensed clothes and limited-edition cups advertising superheroes and sports stars to encourage kids to collect 'em all -- and drink more Slurpees in the process.
    Before coffee was cool, teens got their caffeine fix from sodas they picked up from gas stations after school, a ritual that took off with the Slurpee, she said.
    "It's a fairly inexpensive, yummy frozen thing that comes in way too big servings," Johnson said. "So if you're a teenager with a serious sweet tooth, walking around drinking a Slurpee is kind of a cool thing to do."
    There were apt to be some marketing misfires in desperate appeal to the younger set. In 1970, 7-Eleven released a groovy record based on its signature sugar bomb, aptly titled "Dance the Slurp." Yes, there is a rhythmic slurping solo, and yes, the only lyric is "slurp."

    The Slurpee's biggest fans aren't American

    They're American-made, but no one knocks back Slurpees quite as fervently as Canadians.
    For 20 years and counting, the province of Manitoba has been crowned the Slurpee capital of the world. Not even the harshest winter in decades could deter Canadians from their beloved frozen slush.
    The people of Winnipeg love the slush so much they voted to rename a road "Slurpee Way."
    Slurpee season, Barnes said, is clearly year-round.

    America's obsession with sugary drinks originated in Prohibition

    Americans can blame their sweet tooth on Prohibition, Johnson said. When alcohol was outlawed in 1920, people were forced to seek out a new, legal vice.
    Soda fountains that served shakes and colas took off, and sugar consumption, particularly among white adult men, skyrocketed, she said.
    Frosty, syrupy beverages have even earlier origins, dating back to the Roman empire, when emperor Nero sipped on icy drinks sweetened with honey -- nature's Slurpee.
    "People are just addicted to frozen sweet things," she said.

    The future of the Slurpee is neon bright

    The Slurpee's still kicking after 54 years, but can it endure?
    Johnson has no doubt.
    "I think they're still going to be a purchase of opportunity," she said, adding that as long as people still take road trips and stop at a 7-Eleven to get gas, the franchises will have a consumer base. "They're so cheap, and they're so tempting, and they come in a bajillion flavors."
    The Slurpee has survived even as consumers abandon fast food conglomerates in lieu of fresher, lower-calorie options. Perhaps, Johnson said, 7-Eleven will sub the artificially flavored syrups for a fruit-based puree in an appeal to health nuts.
    Barnes said the drinks remain popular among the generation of consumers who were teens when the slush got popular.
      "For older Slurpers, Slurpee drinks bring back nostalgic memories of school's out, fun-in-the-sun summers and sharing with family," he said.
      And for those who haven't tasted the Slurp's technicolor magic, there's no better opportunity than today to join the club. After all, it's free.