The Original Patent for the Slurpee Maker

"The machine produces a particularly good and unique drink or confection."

On a sweltering August day, what better to cool you down than a "semi-frozen drink comprising tiny frozen particles each of which contains the proper proportions of water, flavoring and carbon dioxide." Mmmmm.

What, that doesn't sound refreshing?

Okay, okay. How about if we just call it a Slurpee, which is what the language above actually describes, according to the original United States patent filing for what would come to be known as the Slurpee machine.

The idea for the beverage as we know it today came from Omar Knedlik, a Kansas Dairy Queen owner who, in the 1950s, began serving bottles of soda that had been sitting in the freezer. Customers loved the slushy consistency, so, according to the Kansas Historical Society, Knedlik began tinkering with ways to modify old ice-cream makers to produce soda slush. One prototype machine used a car air conditioning unit. Knedlik enlisted the help of Dallas-based engineers and branded his drink the ICEE. (Convenience chain 7-Eleven licensed the product and gave it the Slurpee name.) And in 1967, the patent for a "machine for dispensing semi-frozen drinks and control therefor" made it official.

Though the invention could be used for soft ice cream, too, the machine "produces a particularly good and unique drink or confection made from water and flavoring mixed with carbon dioxide gas," its inventors explained in the original filing. Here's a sketch from the original patent

The key was balancing temperature and pressure just so, in order to get the right viscosity and temperature. How it worked: Water and flavor were combined and poured into the machine in liquid form, then gaseous carbon dioxide was added. A refrigeration system cooled the mixture. Then, a pump designed to achieve the desired consistency would respond to the level of pressure in the container by opening and closing—which in turn regulated the temperature and kept the mixture from either freezing or or melting. 

The Slurpee was an instant hit, and enough of a cultural force to produce its own unbelievably 1970s record single called "Dance the Slurp" (which you can listen to below). Today, people slurp 13 million of the slushy beverages each month, with nearly 6.5 billion sold since Slurpees were invented.

That's "almost enough," 7-Eleven says, "for every person on the planet."