What happens to a San Francisco sourdough bread when it leaves San Francisco?

Boudin Bakery's team of bread makers and a cadre of newly-hired local workers will find out over the next few weeks, as the chain prepares to open a new store in Santa Rosa at the Montgomery Village shopping center.

On Tuesday, Boudin staff traveled from San Francisco to deliver 20 pounds of the "Mother Dough," which directly traces its bacterial roots back to 1849.

That's when Isadore Boudin made the bakery's first sourdough starter, known as the "Mother Dough," by mixing flour and water and capturing ambient bacteria and yeast in the air, the company said.

"He started baking with the old French technique, but when he baked in San Francisco .... the spores that live in San Francisco, the wild yeast and bacteria, changed the flavor of his dough," said Fernando Padilla, master baker for Boudin. "The dough changed, and it got more sour, and it got kind of tangy, with a very fine crust."

There's a reason why San Francisco sourdough bread has its own flavor. The wild bacteria and ambient yeasts in the air aren't found elsewhere, and they impart a unique flavor on the bread.

To keep that flavor profile going, Boudin bakers kept that sourdough starter alive for 164 years, the company said.

"All you need to do is add flour and water continuously every day, and she will keep growing," Padilla said.

A 20-pound starter, which was delivered Tuesday to the Santa Rosa store, can be used to make about 500 pounds of bread, Padilla said. Over the next three weeks, before the Santa Rosa store opens July 11, Boudin will be training about 45 new employees and testing out the new ovens, a spokeswoman said. The hiring of cooks, bakers, cashiers and guest attendants is almost complete, she said.

The sourdough starter will not take up permanent residence in Santa Rosa. If it spent too much time outside San Francisco, its character would change as the yeast in Sonoma County's air and the minerals in its water make their mark on the fermenting mix.

So instead of keeping the sourdough starter alive in Santa Rosa, the local Boudin store will rely on the San Francisco headquarters to deliver more starter from the city every few weeks.

"When it gets diluted, we'll bring more from San Francisco," Padilla said.

So, why would someone want to eat something with ingredients that are so old?

"I tell people it's like a seed," Padilla said. "Every day, you take a seed out, and you use a portion ... and it keeps growing."

So far, there are no plans to make a Sonoma County-themed sourdough, company representatives said.