Thousands of years ago, the story goes, a shepherd filled his leather water pouch with cool, crisp water from a high mountain stream in the Caucasus Mountains. In the water were curdlike "grains" of kefir, a live, active "starter" that naturally fermented in the water, creating a beverage rich with beneficial bacteria — what we now call probiotics.

Or, maybe it was monks in Tibet who cultivated these magical bits of fermented goodness, then presented them to Mother Teresa of Calcutta as a gift. Then again, maybe water kefir grains were first discovered in Mexico, where their existence was first documented in 1899, occurring in the naturally sugared water of the Ountia cactus.

The point is, water kefir grains have been around for a long time, propagated and used by cultures throughout the world, says Tom Boyd, owner of the newly opened Kefiry in Sebastopol. The tiny shop is where Boyd and his business partners, Jeffrey Edelheit and Deana Dennard, age and sell their naturally-fermented sodas, called Enlivened.

"We are the first live-cultured soda sold in America," says Boyd. "It's really a living drink," he adds.

If this is all Greek to you, you're not alone. Because most Americans aren't familiar with this ancient fermentation process, Boyd's job is as much about education as it is selling his soda. That's where a glass beaker filled with what looks like lemonade and sediment comes into play. Tiny bubbles rise through the fluid, created by the kefir grains at the bottom — carbon dioxide being released by the hungry, sugar-eating bacteria.

"There are 30 to 60 bacteria colonies inside and as many micro-organisms as all the people on earth," said Boyd. The kefir grains self-propagate, and can be grown and shared with others, not unlike sourdough starter.

Like dairy kefir, which has been popularized as a health tonic, water kefir is a fermented food that is thought to promote digestion and healthy flora in the digestive system. Unlike dairy kefir, water kefir grains are lactose-free.

But it's a lot easier just to explain water kefir as naturally fermented soda that contains no alcohol and only a small amount of sugar. Flavors include Holy Basil, Dragon's Blood (with hibiscus), Tulsi Kola (which tastes the most similar to Coke) and lemon-ginger.

Boyd and Edelheit have perfected the production over the past eight years, breaking down the entire process, from the kefir grains to a proprietary water purifying technology.

"This is really going back to our ancestors. Before the industrial revolution, most beverages were fermented," says Boyd. In the back are buckets of the grains, which look like little florets of milky gelatin. Eaten raw, they're a bit floral in flavor, but unremarkable. Fermented with herbs like lavender, basil or hibiscus and their own specially filtered water, they're a fizzy, more healthful alternative to sugary drinks. Boyd suggests that the combination of purified water and kefir can help the body's immune system and provide antioxidants in addition to beneficial bacteria for the body.

Whether or not probiotics like water kefir are a panacea is something scientists are still debating, though current literature points to a number of health benefits. But there's no doubt that The Kefiry is fermenting a loyal local following.

Want to try it? The Kefiry, 972 Gravenstein Highway S., #120, Sebastopol. You can try their water kefir on tap at the Arlene Francis Center's new cafe at 99 Sixth St., Santa Rosa.

(You can read more Backstories about fascinating local people at BiteClubEats.com/backstory. Want to suggest someone to be featured in a future Backstory? Email Heather at heather.irwin@pressdemocrat.com.)