A starter is a place: why sourdough travels badly and does it anyway

A sourdough starter is a culture of wild yeasts and lactic acid bacteria living in a paste of flour and water. It is kept alive by regular feeding, and under reasonable conditions it can be maintained more or less indefinitely.

Bakeries advertise starters that are decades old, and a few claim considerably more. Families carry them when they emigrate, sometimes dried onto cloth, sometimes as a lump in a jar in hand luggage. There is genuine sentiment attached, and it is worth asking what exactly is being carried.

What is actually in there

A mature starter contains a community — typically several species of yeast and a larger number of lactic acid bacteria, often in ratios where the bacteria substantially outnumber the yeasts. The yeasts produce carbon dioxide, which raises the dough. The bacteria produce lactic and acetic acid, which give the flavour and the keeping quality, and which lower the pH enough to discourage things you would not want growing.

The specific composition varies. Some species turn up in starters worldwide; others are more regional. And the community shifts over time in response to how it is kept.

The uncomfortable finding

Researchers have looked at what happens when starters move. In one widely discussed study, bakers from different countries were given identical flour and identical instructions, made starters, and brought them together — and the microbial communities were substantially shaped by factors that had nothing to do with geography, including the bakers' own hands.

Other work has found that when a starter is moved to a new environment and fed different flour, its microbial composition changes over subsequent weeks. The community adapts to the new inputs.

Which raises an awkward question about the hundred-year-old starter. Is it the same organism population that crossed the ocean in 1912, or is it a continuously maintained culture in the same jar, whose members have turned over many times?

The honest answer is closer to the second. What persists is the practice — the feeding schedule, the jar, the habit — and the culture inside it is a rolling population shaped by the flour it is currently eating.

This is not a debunking

It would be easy to treat this as a deflation, and it is not.

The flour matters enormously, and flour is a place. Wheat varieties, milling method, extraction rate and whether the grain is stone-ground all affect what grows. A starter fed on locally milled rye in a cold kitchen in northern Europe develops into something genuinely different from one fed on high-protein white flour in a warm bakery elsewhere.

So the starter is not a relic carrying a fixed population. It is more like an instrument that keeps being retuned to the room it is in — which is, if anything, a better metaphor for what people mean when they talk about food and place.

The temperature dial

The variable most bakers underuse. Warmer fermentation tends to favour the organisms producing lactic acid, giving a milder, yoghurt-like sourness. Cooler and slower tends to produce more acetic acid, giving a sharper, more vinegary edge.

This is why the same starter produces noticeably different bread in summer and winter, and why bakers who move house often find their bread changes before they have altered anything else.

Hydration does similar work. A stiffer starter and a wetter one develop differently, and traditions differ on this — some European practices maintain a firm, dough-like culture; others keep a liquid one.

The traditions that are not called sourdough

Naturally leavened bread is not a European speciality, though the current vocabulary makes it sound like one.

Injera, made from teff in the Horn of Africa, is fermented over days and produces its characteristic sourness and its honeycomb surface from the same basic biology. Idli and dosa batters in southern India are fermented mixtures of rice and lentils, leavened by wild organisms. Various steamed and griddled breads across Asia use similar principles.

Each of these is an independent solution to the same problem: how to make grain more digestible, better tasting and longer keeping, using nothing but time and the organisms already present.

What to do with a starter someone gives you

Feed it with whatever flour you can get locally rather than trying to replicate the original. It will change. That is not a failure of stewardship — it is the culture doing what cultures do.

Keep a dried backup. Spread a thin layer on parchment, let it dry completely, and store it somewhere cool. Dried starter revives reliably, and it removes the anxiety that makes people treat a jar of flour paste as an heirloom too precious to use.