SAN FRANCISCO (KRON) – It’s a staple of every San Francisco vacation itinerary — a sourdough bread bowl of clam chowder at Boudin Bakery while surviving the chills on Fisherman’s Wharf.

But why? And why does sourdough bread have such a strong connection with the City by the Bay in particular, and California in general?

The answer dates all the way back to the Gold Rush.

As columnist Carl Nolte wrote in a 1999 San Francisco Chronicle piece, French baker Isadore Boudin used the sourdough yeast common at the time to make French-style bread, creating the distinct California sourdough we know and love today.

Sourdough yeast was very common in the 19th century, and thus was often mixed with flour to create bread. Until it was replaced by barm from the brewing of beer, in the 1870s (and subsequently by cultured yeasts), it was the standard way of leavening bread.

But Boudin’s sourdough French bread grew into a life of its own, growing in popularity even as sourdough itself fell out of fashion in much of the world.

What gives the recipe its unique sourness is a local bacteria, fructilactobacillus sanfranciscensis (named for the city’s Latin moniker, of course), that thrives in San Francisco’s foggy, coastal climate. This makes it hard to replicate in other environments.

But while the Boudin Bakery may have spread to 29 locations, at least one of which is as far as San Diego, it will always feel most natural right where it was born.