A sourdough starter is a stable ecosystem, not a temperamental pet

The theory of how a sourdough starter works is well covered elsewhere. This is about the version you meet in practice.

What is living in the jar

A mature starter contains wild yeasts and lactic acid bacteria in a stable partnership, with the bacteria typically far outnumbering the yeast. The bacteria produce lactic and acetic acid, dropping the pH to a level most spoilage organisms cannot tolerate.

The yeasts produce the carbon dioxide that lifts the bread and are comfortable in that same acidic environment. This mutual arrangement is why a starter kept in reasonable conditions does not go bad in the way a bowl of flour and water would. The specific organisms vary by flour, kitchen and feeding habit, which is why starters behave differently in different homes.

Feeding ratios and what they control

A one to one to one feed, meaning equal weights of starter, flour and water, will typically peak in four to six hours at 24C. A one to five to five feed dilutes the culture heavily and might take ten or twelve hours to reach the same point. Larger feeds do not weaken the starter; they simply give the organisms more food and therefore more time before they run out.

Weighed out, this is the lever to use when you want a starter ready at a particular hour rather than whenever it decides. Keep the flour consistent, because switching between white and wholemeal changes the timing as much as the ratio does.

Reading the peak

A starter is at its most active when it has risen to its maximum and is just beginning to flatten on top. Using it well before the peak means fewer active organisms; using it long after means a hungry, acidic culture with less lifting power. The float test, dropping a spoonful in water to see if it swims, is a rough indicator and fails on stiff or wholemeal starters.

The dough tells you first: a rubber band or a marker line on the jar tells you far more, because you can see the rise directly. Peak time is repeatable in a stable kitchen, which is what makes planning a bake possible.

Storage between bakes

In the fridge a fed starter will hold for a week or two with no attention, slowly acidifying but remaining viable. Bringing it back usually takes two feeds at room temperature over a day, and the second will be visibly more vigorous than the first.

At oven temperature, a dark liquid on top, sometimes called hooch, is alcohol from a hungry culture and is a feeding signal rather than a spoilage sign. Pour it off or stir it in, feed, and the starter recovers without drama.

Genuine spoilage looks like fuzzy or coloured mould, and that jar should be thrown away rather than rescued.

Stiff versus liquid starters

A stiff starter at around 50 to 60 per cent hydration favours acetic acid, producing a sharper, more pronounced sour note. A liquid starter at 100 per cent hydration or more tips towards lactic acid, giving a milder, creamier acidity.

Once the crumb sets, stiff starters also ferment more slowly and keep longer between feeds, which suits an irregular baking schedule. Neither is better; they are two settings on the same instrument and you choose the flavour you want. Changing hydration takes a few feeds to settle, so judge the result on the third or fourth cycle rather than the first.

Proving times are written for a warm kitchen, and yours may not be one.

Troubleshooting without panic

A starter that has stopped rising is almost always cold, underfed or being fed too much flour relative to its strength. Move it somewhere warmer, feed it at a smaller ratio such as one to two to two, and give it two or three cycles. A vinegary smell means acidity has built up, which more frequent feeding corrects within a day or so.

Discarding feels wasteful but exists to keep the population from drowning in its own acid and waste. The most common error is impatience, since a genuinely struggling starter usually needs days, not a new recipe.

The takeaway

Feed it on a rhythm, watch the peak, and stop treating a competitive ecosystem as delicate.

Bake it badly once on purpose. The failure teaches more than the photograph.