Building the Perfect Slurpee

What emerged from the research competition was a caffeinated, zero-calorie, nonfat product with 2 grams of sugar in an eight-ounce serving, 25 milligrams of sodium and 2 grams of carbohydrates.

Even as makers of frozen carbonated drinks work on the next diet flavor, none is ready to give up on the sugar-laden slushes that have made the category popular.

"In most of our locations we have two valves, two different purchase options for consumers," said Susan Woods, the vice president for marketing at Icee, based in Ontario, Calif. "To devote one of those strictly to diet is giving up a lot. There's less people who are looking for a diet than there are who are looking for a cherry."