When is my sourdough starter ready to use?

The rise, the peak and the fall

After a feed the yeast multiply and the starter rises. At the peak it is domed with the most gas; then, as the food runs out, it falls and leaves streaks on the glass. Bread rises best from starter used in the window around the peak. Mark the level with a rubber band right after feeding so you can see the rise.

Signs to check

If it doubles but slowly (over 12 hours at 75°F), it is alive but not strong yet: keep feeding twice a day for a few days. See too weak. Smell it too: a mild sour or alcohol smell is normal, but a smell that is not its usual clean, sour one, fuzzy mold, or pink or orange streaks mean throw it out, not bake with it (when to throw a starter out).

• Volume: at least double the level you marked.
• Top: domed, or just beginning to flatten.
• Bubbles: through the whole jar, not only on top.
• Texture: airy and webby when you pull a spoon through it.
• Smell: yeasty, mildly sour, a little fruity.

The float test

Drop a spoonful into water. If it sinks, it is not ready yet, King Arthur says. If it floats, that does not mean it is ready: in King Arthur's own test a fed starter floated to the top hours before it was ripe. A float is no substitute for the rise: wait until it has doubled and is domed and bubbly, as above.

Making the peak fit your day

Choose the feeding ratio by when you want to mix. In King Arthur's test at 78°F, 1:1:1 peaked in about 4 to 6 hours, 1:2:2 in about 8 and 1:4:4 in about 12; a higher ratio such as 1:5:5 takes longer still. The bread timeline planner works back from when you want to bake.