Looks like Starbucks is sweating out the summer heat wave, too.

Heavy demand for its cold, blended Frappuccinos during the morning, which can take longer to churn than hot beverages, slowed service and sales during a sweltering July. July sales grew at the slowest pace in nearly five years.

The company's stock sank 8 percent yesterday, down $2.66 to $30.64.

"They haven't been able to handle the demand. They've been besieged," says Dan Geiman, analyst at McAdams Wright Ragen. But, he adds, "It's probably a blip."

Starbucks executives began to notice the problem as temperatures climbed in mid-July. Sales at stores open at least a year rose 4 percent in July; the previous July they rose 7 percent. Among the states hardest hit: California and Texas.

Starbucks executives downplayed the July jam. "We're going to get it solved," CFO Michael Casey told analysts in a conference call.

The stock plunge comes as some restaurants — particularly such casual-dining chains as Outback Steakhouse, Applebee's and Cheesecake Factory — have struggled. Some customers are grappling with rising energy costs and credit card interest rates. Those factors may also affect Starbucks, particularly among the lower-income consumers the chain has attracted as it expanded, Geiman says.

The larger issue may be: Can a company that made its mark selling quality hot beverages in a flash turn on a dime and sell quality cold, blended beverages as quickly?

The answer depends on whom you ask. CEO Jim Donald says additional baristas will be assigned to work peak hours.

But retraining thousands of employees to blend cold drinks faster can take a while. Starbucks employees are trained as baristas, "not smoothie or blended-drink makers," says Sherri Daye Scott, editor at QSR Magazine.

Needed equipment changes probably won't resolve the problem until next summer, although things could improve this month as the weather moderates and Starbucks introduces its Tangerine and Creme Frappuccino, UBS Investment Research's David Palmer said in a research report yesterday.

Even with the cold-drink problems, Starbucks' latest quarter net earnings rose 16 percent from the same period last year to $145.5 million on revenue of $2 billion, up 22.6 percent. Excluding a 1-cent tax benefit, Starbucks' income met the 17-cent forecast of analysts surveyed by Thomson Financial.

In a nod to overheated consumers in New York City, Starbucks lured crowds by promoting free iced-coffee drinks.