Guides · Updated 23 October 2026
How to make a sourdough starter
A starter is flour and water left to ferment until wild yeast and lactic acid bacteria take over. You need a jar, a kitchen scale, whole-grain flour to begin with, and about 7 to 14 days.
What you need
- A clean glass jar of about 500 ml with a loose lid
- Whole-wheat or whole-rye flour for the first days, then bread flour or a mix
- Water at room temperature. If your tap water is heavily chlorinated, let it stand for a few hours or use filtered water
- A scale. Volume measures are too inconsistent
Day by day
| Day | What to do | What you will likely see |
|---|---|---|
| 1 | Mix 50 g whole-grain flour and 50 g water. Cover loosely. | Thick paste, nothing much happens. |
| 2 | If nothing has changed, just stir. Otherwise discard all but 50 g and feed 50 g flour + 50 g water. | A few bubbles, possibly a sudden rise. |
| 3–4 | Discard to 50 g, feed 50 g flour + 50 g water once a day. | Activity often drops. This is normal: the early bacteria die back before the stable culture develops. |
| 5–7 | Keep feeding daily. Switch to twice a day if it rises and falls within 12 hours. | Yogurt-like, tangy smell and regular bubbles. |
| 7–14 | Feed 1:2:2 or 1:5:5 once it is predictable. | Doubles within 4 to 8 hours of feeding, at roughly 24–26 °C. |
Use the starter feeding calculator to get grams for any ratio.
Is it ready?
Your starter is ready when it reliably doubles after a feed, has a domed bubbly top and smells pleasantly sour. The float test (a spoonful floating in water) is a rough sign only; a high-hydration or whole-rye starter can sink and still be perfectly active.
Troubleshooting
- Grey liquid on top (hooch): the starter is hungry. Pour it off or stir it in, then feed.
- Smells like acetone or nail polish: also hunger. Feed more often or at a higher ratio.
- Pink, orange or fuzzy mould: throw it away and start again with a clean jar.
- No activity after a week: move it somewhere warmer and use whole-grain flour.
Tools for this guide
Hydration calculator · Baker's percentage calculator · Starter feeding calculator