Before there was commercial yeast in a packet, there was the starter: a living culture of wild microbes, kept alive by regular feeding, that a baker could use to leaven bread indefinitely. A good starter was a possession of real value, tended for years and passed between generations, and in the harsh mining camps of the nineteenth-century frontier it became something close to a treasured pet. Prospectors in the Klondike and Alaska protected their sourdough cultures with such devotion — keeping the pot warm inside a coat, or even in the bedroll on a freezing night — that the men themselves came to be called "sourdoughs." The bread gave its name to the miners.
What a starter actually is
Sourdough is the oldest form of leavened bread, predating the deliberate use of purified yeast by thousands of years. Its rise comes not from a single organism but from an ecosystem. A starter is simply flour and water left to ferment, into which wild yeasts and bacteria settle from the flour, the air and the baker's hands. Two kinds of microbe do the work in partnership. Wild yeasts consume the sugars in the flour and produce carbon dioxide, which leavens the dough and makes it rise. Alongside them live lactic acid bacteria — lactobacilli — which produce the acids that give sourdough its characteristic tang and, not incidentally, help preserve the bread and keep hostile microbes at bay.
The most famous of these bacteria carries a name that fixes it to a city: Lactobacillus sanfranciscensis, first identified and named by researchers in the 1970s from the sourdough cultures of San Francisco. San Francisco sourdough is prized for its distinctive sharp sourness, and for a long time it was believed that something in the city's fog-cooled air or local conditions gave the bread its singular character. The reality is subtler — the microbial community of a starter depends on flour, temperature, feeding schedule and the hands that tend it as much as on geography — but the city's association with the bread is genuine and old. The Boudin Bakery in San Francisco, founded in 1849, claims to have kept a mother starter going since the Gold Rush itself, feeding a fragment of the original culture forward for well over a century and a half.
The Gold Rush connection
The link between sourdough and gold is no coincidence. When tens of thousands of hopeful miners poured into California in 1849, and later into the Klondike and Alaska in the great northern gold rushes at the end of the century, they needed to feed themselves in places with no bakeries, no shops and no reliable supply of fresh yeast. A sourdough starter was the perfect solution: it needed only flour and water to keep alive, it travelled, and it could produce bread, biscuits and flapjacks wherever a fire could be lit. A miner who let his starter freeze or die had lost his means of making bread, which is why the culture was guarded so jealously and kept warm at all costs.
So closely was the starter identified with the men who carried it that "sourdough" became frontier slang for an experienced prospector — someone who had survived at least one winter in the north, as opposed to a green newcomer or "cheechako." The bread and the identity had fused. To be a sourdough was to be a seasoned veteran of the goldfields, defined by the living culture kept alive in one's pack.
Starters older than the people feeding them
The most remarkable quality of a sourdough starter is its potential immortality. Because it is a self-renewing culture, a starter that is regularly fed can outlive not only its original owner but many generations of them. Bakers today maintain starters that are decades old, and some claim lineages stretching back a century or more, fed forward daily or weekly in an unbroken chain. The living organisms in the pot are constantly replaced as they divide, so no single microbe is ancient; what persists is the culture, the community, handed on like a family heirloom that must be fed to survive. People give their starters names and leave them in wills.
There is a lovely paradox in all of this. Sourdough is at once the most primitive of breads — the method by which humanity leavened its loaves for millennia before anyone understood what yeast was — and the object of intense modern fascination, revived in home kitchens whenever people rediscover the pleasure of making bread from almost nothing. A jar of flour and water, left alone, will fill with life; feed it, and it will feed you, potentially for longer than you will live. The prospectors who slept beside their starters understood something that the industrial packet of yeast made easy to forget: that leaven is not an ingredient you buy, but a living thing you keep.
Quiz nuggets
- Sourdough is the oldest form of leavened bread, predating the use of purified commercial yeast by thousands of years.
- It rises through a partnership of wild yeasts, which produce carbon dioxide, and lactic acid bacteria, which produce its sour tang.
- The bacterium Lactobacillus sanfranciscensis was named after San Francisco, whose sourdough is prized for its sharp sourness.
- Gold Rush and Klondike prospectors were nicknamed "sourdoughs" for the starters they guarded and kept warm.
- A regularly fed starter can outlive its owner; the Boudin Bakery of San Francisco (founded 1849) claims a starter dating from the Gold Rush.