Last year, Starbucks (NASDAQ:SBUX) sent a warning shot across Green Mountain Coffee Roasters(UNKNOWN:GMCR.DL) nose with the introduction of the Verismo brewing system. As the latter's K-Cup patent expired and generics flooded the market, investors ran for the hills with the idea of do-no-wrong Howard Schulz moving his company in direct competition. Now, another home-brew innovator may be shaking in its boots as Starbucks has begun offering a new product in select stores. Should SodaStream (NASDAQ:SODA) investors fear the Seattle juggernaut?

Starbucks soda?
Most are aware that Starbucks has branched out beyond the typical coffee and espresso offerings. The company offers energy-infused fruit beverages, smoothies, and a full line of accessories in thousands of locations. It's part of the reason that Howard Schulz may be the most beloved CEO in the country. At least, his shareholders think so.

It looks like that product expansion isn't slowing down, either. The company has rolled out new products in some stores, including an artisanal root beer, and ginger and lemon ales. They are only available at approximately 10 stores in the Seattle area, but a Starbucks blog quoted in BusinessWeek used language such as "crazy good" to describe the root beer. Given that Starbucks clearly has the ability to offer quality home brewers to its loyal customer base, are we going to be able to make Starbucks soda in the comfort of our homes?

The Verismo has been a moderate success for Starbucks, but not really an issue for Green Mountain. The machine bridges a gap between traditional Nespresso-style machines and the Keurig, but it isn't really intended to replace either.

If the soda products test well, and I would be willing to bet they will (given the summer months are upon us), brace for a nationwide rollout of these tasty beverages. Will the company move into a home soda machine a la SodaStream? It's certainly possible. Should SodaStream investors be worried? I don't think so. The company's sales grew 50%  last year and it is the de facto name in the segment. Starbucks may be able to steal some market share, but I think it will be negligible to SodaStream's business.

Now, admittedly, this is merely speculation. There are a variety of paths the company can take -- including partnering with SodaStream, but given the tremendous ambition of Starbucks, it's far from fantasy.

Investors in SodaStream have little to worry about at this time. The company has hit 1% market penetration in the U.S. -- an incredible feat, but leaving much room to grow. On a forward-looking basis, the company is even cheaper than the soda giants, Coca-Cola and PepsiCo. You may soon be seeing tasty carbonated ales at a Starbucks near you, but don't let it spook your portfolio.

Fool contributor Michael Lewis has no position in any stocks mentioned. The Motley Fool recommends Coca-Cola, Green Mountain Coffee Roasters, PepsiCo, SodaStream, and Starbucks. The Motley Fool owns shares of PepsiCo, SodaStream, and Starbucks. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.