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The day began with heavy rain soaking San Francisco’s hilly streets. But as we made our way to the Ferry Plaza Farmers Market, walking along the seagull-dotted piers that jut out onto the bay, the sun began to cut through thick fog and silvery clouds. We wandered past artisanal cheese stands, organic chocolate shops and vendors hawking avocados and oranges. As the briny air wet our cheeks, a familiar craving arose; my stomach was longing for that San Francisco tradition: sourdough bread.

Sourdough is the quintessential San Francisco comfort food, with yeasty and earthy aromas wafting out of the city’s bakeries, hinting at warm loaves fresh out of hearth ovens. Thick and hollow, sourdough is crusty on the outside and soft and chewy on the inside. Its complex taste is uniquely tangy, thanks to the pre-baking fermentation process that creates naturally occurring lactose acid, strains of wild yeast and copious flavours. In the San Francisco Bay Area alone, more than 3.5 million sourdough loaves are baked each week.

Bake like an Egyptian
“Sour” dough, one of the oldest known fermentations, likely began accidentally in Ancient Egypt around 4000BC. As the story goes, an Egyptian baker on the Nile set out to make unleavened flat bread with grain porridge, but left the dough to rest too long and wild yeast took hold; once baked, the bread naturally puffed up. Archaeologists and food historians point to both Egyptians’ well-documented relationship with yeast and remnants of sourdough discovered in Ancient Egyptian sites as evidence to this theory.

For centuries, the process uncovered in Ancient Egypt was the only form of leavening available, and generations throughout the Middle East and Europe passed down their recipes. It was not until 1860, when French chemist and microbiologist Louis Pasteur identified yeast as the cause of fermentation, that it was subsequently isolated and produced commercially for bakers.

All sourdough begins with a starter: a mixture of flour and water that is left to ferment for days – and in some cases years – at room temperature, creating a bubbly, sour mixture of wild yeast and bacteria. As long as flour and water are replenished to the starter, the dough remains active and its cultures alive. In just two cups of starter – enough to make a loaf – there are more than 200 million yeasts and 20 billion lactobacilli bacteria.

Sourdough rush
It is not clear when sourdough first landed in the United States. Local legend points to Basque immigrants who migrated to South America, mainly Argentina and Paraguay, during the Spanish civil wars of the 1830s. When news hit of gold in Northern California, thousands of Basque and pioneers from across North America rushed to San Francisco in search of wealth. From 1847 to 1849, the city’s population swelled from 1,000 to more than 20,000.

Lore credits these Basque migrants as the original carriers of sourdough starter. Sourdough was soon a staple of the miners who relied on it to make biscuits, breads and pancakes at their camps. They would mix flour into portions of their starters each morning, then slowly bake the blend in a large cast iron pot fitted with a lid, placed on coals in the ground and covered with dirt. Each night when they would arrive back at camp after a long, arduous day, the bread was baked, warm and ready to fill their bellies. So common were the loaves in the gold camps that “sourdoughs” became a nickname for the miners themselves (who – they say – slept hugging their starters to keep them warm).

San Francisco’s wild child
The Gold Rush is firmly entrenched in San Francisco’s history, its legends and traditions woven into the city’s fabric. Sourdough is no exception. The hyper-sour taste unique to San Francisco has taken it from a miner’s calling card to the modern urban dweller’s go-to bread, legendary around the world and iconic to the foggy city by the bay.

The principal wild yeast strain found in San Francisco’s bread is native to the region and it is the defining factor in its distinctive tanginess. Microbiologists Frank Sugihara and Leo Kline identified the strain in 1969, naming it lactobacillus Sanfranciscensis in honour of the city. Any sourdough starter left to ferment throughout the area will breed this native yeast.

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