SodaStream (NASDAQ:SODA) took a hit yesterday after offering up uninspiring bottom-line guidance for the current quarter, and today it's losing even more of its fizziness after an analyst downgrade.

Stifel Nicolaus is lowering its rating on the shares -- from hold to sell -- and lowering its price target to $40. The analyst wasn't upbeat on the company behind the namesake soda maker system that turns flat water into flavored soda, but SodaStream's third quarter was enough to consider an even bleaker perspective on the stock.

A big sticking point for investors and Stifel Nicolaus is the decelerating growth in the U.S. this past quarter. Sales in the more established Western Europe market actually grew faster than SodaStream's stateside business, and that's something that we just hadn't seen since SodaStream's push into the U.S. three years ago. The recent acquisition of its Italian distributor has helped pad results in Europe, but that still doesn't take away from the less than stellar showing in the U.S. market, where soda consumption per resident is higher than in any other country in the world.

The real shocker is that SodaStream conceded during yesterday's earnings call that flavor sales in the U.S. actually declined relative to last year. Globally, flavor sales were disappointing, inching just 7% higher. However, in the U.S. -- where revenue climbed 36% on the strength of strong starter kit and CO2 refills -- syrup bottle sales fell 2.6%. Are folks using the machines less? That's not right. The carbonator refills continue to run strong. The more likely explanation is that folks are either fine with unflavored club soda or they're coming up with non-SodaStream ways to sweeten their beverages.

It's still not a welcome trend, but is it worth the sharp sell-off that has taken place on Wednesday and Thursday? The U.S. still accounts for less than a third of SodaStream's overall sales. Europe remains a larger market, but it's hard to sway stateside investors and analysts into thinking that this is a global opportunity if the high-margin flavors aren't moving. SodaStream explains this away as retailers engaging in inventory rebalancing, but it's still a trend that those sticking it out will need to keep a close eye on. Year-over-year flavor sales overall have decelerated for four consecutive quarters, and it's been a long way down from a 76% surge five quarters ago to just 7% this time around.

SodaStream has been offering a wide variety of metrics since blasting on the scene as a hot IPO three years ago, but now we know that everyone will be watching one particular gauge with intense interest three months from now. SodaStream had better make sure it puts some more flavor into its flavors.