Summer is coming to an end, but it's not too late to indulge in one of 7-Eleven's (NYSE:SE) delicious and refreshing Slurpees. And now, thanks to a new formula from Pepsi (NYSE:PEP), you can have your Slurpee without all the associated calories (and there are lots otherwise -- 100 per 8-oz. serving).

Today's Wall Street Journalreports (subscription required) that 7-Eleven's new Diet Pepsi Slurpee, launched last month, is enjoying "strong sales increases." This seemingly unremarkable feat is actually the result of some pretty nifty science on Pepsi's part. A Slurpee's smooth consistency is a function of the sugar crystal itself, so producing a non-sugar Slurpee was no simple matter.

7-Eleven approached both Pepsi and Coca-Cola (NYSE:KO) last summer in an effort to develop a suitable diet Slurpee formula. Ultimately, Pepsi's scientists won out with a formula consisting of three sugar substitutes: tagatose, erythritol, and sucralose. The Journal says that tagatose, produced by Spherix (NASDAQ:SPEX), was instrumental in attaining the smooth Slurpee consistency, without freezing up the Slurpee machine as the syrup is mixed at 28 degrees.

Coca-Cola, for its part, told the Journal that it did come up with a Diet Coke Slurpee formula but had concerns about drink quality. Too little, too late for Coke. Like Pepsi's winning bid for Gatorade and Sobe, this marks another instance of Pepsi beating Coke to the punch.