It's hard to find stocks that look particularly undervalued in today's bullish -- and arguably fizzy -- market. However, SodaStream International(NASDAQ:SODA) (NASDAQ:SODA) is refreshingly cheap following investors' sudden, and probably temporary, burst of pessimism. That's why I'm adding even more shares to the real-money Prosocial Portfolio I manage for Fool.com.

I bought shares of Israel-based SodaStream for the second time in October. However, the stock tanked shortly afterward, as many investors fretted about disappointing quarterly results and panicked about weak syrup sales and lower revenue guidance from the maker of home soda-producing machines.

Like many investors, I was bummed that I didn't get shares of SodaStream at the ensuing cheaper price. But since the situation hasn't changed my overall long-term investment thesis, I'm going to add more shares to the portfolio.

Getting over a taste of pessimism
The Prosocial Portfolio's philosophy -- finding solid long-term companies that take socially responsible elements into consideration -- reduces the number of choices as well. Even though the universe of such stocks is expanding rapidly, there are still many companies that don't strongly reflect these qualitative values for the long haul.

SodaStream's fall from grace illustrates overall investor pessimism about this company, which still has plenty of room for growth in consumers' lineup of useful home gadgets.

Even though investors found a lot to dislike in the relatively young company's third-quarter results, there's not much to indicate a reason to panic. Revenue increased 29% to $145 million. Net income dipped negligibly to $16.4 million from $16.8 million on a quarter-over-quarter basis.

With the exception of the Asia-Pacific region, revenue grew in all of SodaStream's geographies. The company is also moving into plenty of other flavors on its own and through partnerships, and these may not have gotten completely on customers' radars yet. In addition, another important part of its business, CO2 canister refills, increased by 34% on a year-over-year basis.

More stores, more syrups
Whether SodaStream's core self-branded syrups need improvement is definitely a concern. However, the company has established relationships with well-known brands like Ocean Spray and Mondelez International's Country Time Lemonade, Crystal Light, and Kool-Aid. It's also trying to attract the party-hearty crowd with its Happy Hour line of cocktail mixers: cosmopolitan, margarita, pina colada, and strawberry daiquiri.

SodaStream also hits on America's interest in healthy alternatives, since its products focus on sweeteners like cane sugar and sucralose, the latter of which is often seen as a better alternative to other diet sweeteners.

And SodaStream creates plain old bubble water, too. Its business also includes CO2 canister sales; CO2 makes the water bubbly. These canisters are available for purchase, and if consumers exchange their spent canisters they get discounts, which fits into both the environmentally minded reduction of waste as well as consumers' budget consciousness.

Another bullish aspect of SodaStream is its increasing presence in major retail stores such as Wal-Mart, Bed Bath & Beyond, Staples, Target, and Macy's.

Interestingly, according to management on the third-quarter conference call, Best Buy included SodaStream in its advertising of its own volition, and Wal-Mart has called it a momentum brand.

Running down a few risks
For many first movers, imitation may be a form of flattery, but it's also a form of extreme risk, especially coming from well-established companies. Green Mountain Coffee Roasters, which provides the Keurig single-serve coffee machine, filed an application this summer for a trademark for the name "Karbon," a product widely expected to be a direct competitor to SodaStream's do-it-yourself soda machines.

Beverage giant Starbucks plans a product called Fizzio, which similarly carbonates beverages. Investors are probably forgetting, though, that the Fizzio appears to be intended for the institutional market at first, not the household market, although it could branch out into other areas. 

So far, there hasn't been any movement on the make-your-own soda front from either of these big-name companies in terms of actually getting a product on the market. SodaStream still has an edge with an existing product that's already on many major retailers' shelves, increasing distribution and brand recognition. Still, there is certainly the risk that this attractive, nascent niche will be targeted by biggies with big pocketbooks.

Another more logical risk to keep an eye on is SodaStream's inventory, which increased by 40.3% on a year-over-year basis in the third quarter. When inventory increases at a faster rate than sales, it can indicate a buildup of unsold products. SodaStream attributes the increase to the acquisition of its Italian business and business growth. This will be a good area to revisit going forward, with particular emphasis on the holiday season.

Getting a refill
Growth stocks often get slammed when investors get any impression of negative tidings. But when you still feel strongly about the company's future, this is one of the best times to buy or add to your position.

I don't always anchor on price when I purchase stocks; some of the stocks in the Prosocial Portfolio strike me as good buys regardless, as long as investors believe in the long-term growth story and plan to hold for long periods of time. Stock-price seesaws and changing investor sentiment can sometimes cause fears about whether fundamental businesses are well positioned for the very long haul or not.

Like many investors, I'd certainly prefer to get good deals when I can find them. Right now, I'm finding a good deal in SodaStream.

Gunning for growth
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Alyce Lomax owns shares of Starbucks. The Motley Fool recommends Green Mountain Coffee Roasters, SodaStream, and Starbucks. The Motley Fool owns shares of SodaStream, Staples, 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.