How Can You Tell When Sourdough Starter Is Ripe?

The first indicator is volume, not the clock. After feeding, place a rubber band or piece of tape around the outside of the jar to mark the starter’s level. When the starter rises past the mark and reaches about 2 times its starting volume, it is nearing its peak. Use a clear, straight-sided jar so the rise can be read accurately. At its peak, the starter has a domed surface; if the center has begun to sink, the peak has passed. Starter that has passed its peak can still be used, but the bread will be more sour and may have slightly less volume. The shape of the jar matters too: the rise is much easier to see in a narrow, tall container, while the same increase can be missed in a wide bowl.

The second indicator is the surface. A ripe starter has plenty of bubbles on its surface and around the sides; viewed through the side of the jar, its interior looks spongy. If there are no bubbles or very few, the starter is not ready. The third indicator is the smell: ripe starter smells sour and fruity. A sharp vinegar smell indicates that the peak has passed, while no smell indicates that the starter is not active yet. Read all 3 signs together; none is sufficient on its own.

The best-known test is the float test. Carefully drop one 4 ml measure of unmixed starter into a glass of lukewarm water. If the starter stays on the surface, it has accumulated enough gas and is ready to use; if it sinks, it is not ripe yet. The test is not perfect: a very watery starter may sink because of its density, while a starter that has passed its peak may still float. For this reason, do not use the float test on its own; assess it together with the starter’s volume and smell.

The starter generally reaches its peak in 4–8 hours, but conditions can shift that range considerably. It peaks much earlier in a warm kitchen and takes longer in a cool kitchen. The feeding ratio matters too: adding a lot of flour and water makes the starter peak later, while adding less makes it peak earlier. The flour also makes a difference; a starter fed with whole-wheat or rye flour becomes active noticeably faster than one fed with white flour.

If the starter is not ready, do not mix the dough; wait. If rushed, the dough will not rise and the batch will be lost. If the starter remains weak, give it 2–3 consecutive feedings and watch whether it rises higher and faster after each one. Plan around this timing: decide when to mix the dough, then feed the starter in advance so it peaks at that time. This is the part of working with sourdough that takes the most practice. If you miss the peak, feed the starter again and wait; adding it to the dough after the peak has passed will reduce the loaf’s volume from the start.