Sourdough starter

Why

A sourdough starter is a mix of flour and water in which lactic acid bacteria and wild yeasts live; the bacteria usually outnumber the yeasts about a hundredfold and produce lactic and acetic acid, while the yeasts mainly make the carbon dioxide that raises the dough (see the Yeast dough card). In Czech recipes for buns and dumplings, however, “kvásek” usually means yeast mixed with milk, sugar and flour, not this culture. A new starter settles after 1–2 weeks of regular feeding: in the first days it is often lively thanks to other microbes from the flour, then it goes quiet, and only once lactic acid bacteria and acidity take over does it rise reliably. Warmth and time control the acidity: in the warm a starter ripens within a few hours, and if it stands long past its peak it goes hungry, the yeasts weaken and the acidity rises, so the bread turns out dense and sour; in the fridge everything slows down. Rye bread needs the acidity, because it curbs the enzymes of rye flour that would otherwise break down the starch and leave the crumb gummy.

How to do it

• Start a new starter from wholemeal rye or wheat flour and water at 1:1 by weight; every day remove most of it and feed the rest with fresh flour and water.
• Keep it somewhere warm in the kitchen, not in the cold; it is ready when it reliably rises within a few hours of feeding, is full of bubbles and smells sour.
• Add it to the dough at its peak, when it has risen most and not yet collapsed; feed a sunken, hungry starter first and wait until it rises again.
• Between bakes keep it in the fridge and feed it about once a week; the day before baking feed it once or twice in the warm to wake it up.
• Pour off or stir in grey liquid on the surface that smells of alcohol, the starter is just hungry; skim off a thin, flat white film and feed the starter.
• Do not scrape off fuzzy mould of any colour, pink or orange spots or streaks, or a putrid smell: throw the whole starter away and wash the jar.

If it goes wrong

Move a starter that does not rise after feeding somewhere warm and feed it twice a day for a few days; some wholemeal rye flour also helps. Overly sour bread usually comes from an over-ripe starter or a long rise in the warm; next time add the starter at its peak and shorten the rise. Dense bread that did not rise cannot be made light; slice it thinly or toast it, and return bread that is gummy inside to the oven (see the Baking bread and rolls card). Do not rescue a mouldy starter by removing the top layer, as mould also grows deeper.