Sourdough starter peak calculator

How the estimate works

More fresh flour per part of seed starter means more food to get through, so the rise takes longer. The relationship is roughly logarithmic rather than proportional: doubling the flour does not double the time. At 24°C a 1:1:1 feed peaks in about 5 hours, a 1:5:5 in about 11, and a 1:10:10 in about 14.

Temperature then scales the whole curve. Fermentation roughly doubles in rate for every 10°C, so the same 1:5:5 feed that peaks in 11 hours at 24°C takes around 15 in a 20°C kitchen and about 7 and a half at 28°C. That is why the same routine drifts between summer and winter.

Use the window, not the minute

A starter is usable well before the exact top and for a while after. The window above opens at roughly 85 percent of the way up, when it is domed and lively, and closes as it starts to fall. Inside that window you are fine. What you want to avoid is a starter that peaked and collapsed hours ago, which is the usual reason a well-mixed dough still refuses to rise.

Treat every number here as a starting point. Your flour, your hydration, and how vigorous your culture is all move it. Mark where your own starter actually peaks a few times and you will know your own offset.

Signs it is at peak

Domed on top rather than flat or sunken. Visibly bubbly through the sides of the jar. Roughly doubled from where it sat after the feed, though the exact multiple depends on your flour and hydration. Smelling tangy and yeasty, not sharply acidic. A dip in the middle means you are past it: feed again and wait, or use it knowing the rise will be slower.