How do I keep a sourdough starter alive?

A starter is a stable culture of wild yeast and lactic bacteria living in flour and water. It needs feeding to stay active, but it survives a great deal of neglect, and most starters people throw away were only dormant.

Step by step

1. Feed by weight, not by eye.A 1:1:1 ratio — 50g starter, 50g flour, 50g water — is the standard maintenance feed. Discard the rest before feeding or the quantity doubles every time.
2. Use the right water.Tap water is fine in most of the UK. If your supply is heavily chlorinated, leave it standing for an hour or use filtered — chlorine slows the culture.
3. Choose a schedule that matches your baking.Baking weekly or less: keep it in the fridge and feed once a week. Baking every day or two: keep it out and feed once or twice a day.
4. Take it out the day before you bake.Two feeds at room temperature, eight to twelve hours apart, wakes a fridge starter up fully. A cold starter straight from the fridge is sluggish and gives poor rise.
5. Judge readiness by the rise, not the clock.A healthy starter roughly doubles four to eight hours after feeding and then falls back. Use it at or just before its peak.
6. Use the float test as a rough check.A spoonful dropped in water floats if it is well aerated. It is indicative rather than definitive, but a starter that sinks flat is not ready.
7. Recognise hooch.A layer of grey or brown liquid on top means it is hungry, not dead. Pour it off or stir it in and feed as normal.
8. Recognise genuine spoilage.Pink, orange or fuzzy mould means throw it away and start again. A sharp acetone or vinegar smell means hungry; a smell of nail varnish and mould together means finished.
9. Keep a backup.Spread some starter thinly on baking paper, dry it completely and keep the flakes in a jar. It rehydrates months later and costs nothing.
10. Use the discard.Pancakes, crackers, flatbreads, waffles. Discard is unfed starter, not waste, and it keeps a week in the fridge in its own jar.

Tips

• Fridge and weekly feeding is the realistic schedule for most home bakers.
• Hooch is hunger, not death. Feed it and it comes back within a couple of cycles.
• Dry a spoonful on paper as a backup. It takes five minutes and saves the culture permanently.

Common mistakes

• Baking with a starter straight out of the fridge — The culture is cold and dormant, so it produces very little gas for hours. The loaf underproves and comes out dense, and the starter gets blamed for something the schedule caused.
• Throwing a starter away because it smells sharp and has liquid on top — That is a hungry starter, not a dead one. Two feeds twelve hours apart at room temperature revives almost every starter in that state.

If it doesn't work

Questions people ask