Starter

How to make a sourdough starter in seven days

Updated October 2026 · 3 min read

All a starter needs is flour, water, a jar and about a week of patience. Here is what to do on each day, and what is normal along the way.

What you need

A jar of about 500 ml (2 cups), with the lid resting loosely on top. A rubber band around the outside marks the level after each feed.
Whole rye or whole wheat flour. The bran carries more wild yeast and lactic acid bacteria, and more food for them, than white flour does.
Lukewarm water and a kitchen scale. Weigh flour and water rather than measuring them by volume.
A warm spot: 24–26 °C (75–79 °F) is ideal. Cooler works too, it just takes longer.

Day by day

Day	What to do
1	Stir 50 g flour and 50 g lukewarm water until smooth, cover loosely, leave for 24 hours.
2	Smell it: slightly sour is normal. Add 50 g flour and 50 g water, stir well, another 24 hours.
3	The daily routine starts now: keep 100 g of the mixture, discard the rest, stir in 50 g flour and 50 g water.
4	Repeat the routine. If not much is happening, move the jar somewhere warmer or use a little more whole grain or rye.
5	Repeat and watch: does it rise clearly within 4–8 hours of feeding? If it is very active, you can switch to feeding twice a day.
6	The test: does it double within 4–8 hours of feeding? Then you are nearly there. If not, give it another day of routine.
7	Bubbles throughout, a pleasant sour smell, a reliable rise: your starter is ready to bake with.

Why discard? Without it the mixture grows every day, and the fresh flour is spread across more and more of it. Keeping a fixed amount holds the ratio steady and gives the microbes enough food every day.

What is normal in the first days

Lots of activity on day 2, then nothing. Many starters foam up early and go quiet on day 3 or 4. Those first bubbles come from other bacteria that disappear as the acidity rises. The yeasts and lactic acid bacteria you want take a few days longer. Keep feeding, don't give up.

The smell changes. Yoghurt, vinegar, sometimes a little cheese are all normal in the first week. If it smells like nail polish remover, it is hungry.

Liquid on top is another sign of hunger. Pour it off or stir it in, then feed.

Throw it away only if you see mould: fuzzy patches, or pink, orange or green spots. Then start again in a clean jar.

How to tell it is ready

The most reliable sign is the rise: a mature starter doubles within about 4–8 hours of feeding at room temperature, is full of bubbles and smells pleasantly sour. The often-recommended float test – a spoonful dropped into water – is unreliable, especially with rye.

Once it is ready, it moves into the fridge. How to keep it going there is covered in Feeding your sourdough starter.

Common questions

Can I use white flour?

Yes, but it usually takes longer to get going, because white flour brings fewer microorganisms and less food. A proven approach is to start with rye or whole wheat and switch the finished starter over to white flour gradually.

Can I use tap water?

Usually, yes. If your water is heavily chlorinated, leave it to stand uncovered for a few hours, or boil it briefly and let it cool.

How long does it really take?

Seven days is a good guide at 24–26 °C. In a cool house it can take ten to fourteen days. What matters is not the calendar but whether the starter reliably doubles after feeding.