Sourdough in pizza dough — the guide

One starter, two assumptions. First: it’s kept at 100% hydration— fed equal weights of flour and water — so every gram of starter is half flour, half water. Second: it’s active — recently fed, at or near its peak, not a sleepy jar straight from the fridge.

The dose lives on a much higher shelf than yeast: 2–40% of the flour weight, where fresh yeast runs in fractions of a percent. On a spoon, starter weighs about 15 g per tablespoon — the same conversion the calculator’s “cups” mode uses.

The calculator converts your plan into effective hours — activity doubling every 7 °C, fridge hours counting for little — exactly as it does for yeast, then doses the starter inversely: starter % ≈ 150 ÷ effective hours, clamped to 2–40%.

The anchor worth memorizing: a 24-hour rise at 20 °C wants 6.25% starter — that’s 25× the fresh-yeast dose for the same plan, because a starter is mostly flour and water with the microbes along for the ride.

The fridge row is the practical sweet spot: the cold stretches the schedule, the acidity stays in check, and the dose stays in easy-to-weigh territory. The cold fermentation guide covers that half of the plan.

A starter isn’t an add-on; it’s part of the recipe. The calculator counts its flour and water toward the totals, half and half, and subtracts them from what you add at the mix — so the hydration you chose stays honest.

Worked through 4 × 260 gNeapolitan balls on the 24-hour plan: the recipe’s true flour is 631 g, so the starter is 6.3% of that — 39 g, or about 2 ⅔ tbsp. Its 20 g of flour and 20 g of water come off the adds, and the bowl gets:

Add it up and it’s 1040 g on the nose — four balls of 260 g, at exactly 62% hydration once the starter’s water is counted. No spreadsheet required; switching the yeast type to sourdough does all of this.

The model assumes a starter at the top of its game, and that part is on you. Feed it 4–8 hours before mixing (at warm room temperature) and use it at its peak: domed, airy, roughly doubled, smelling of yogurt and ripe fruit rather than vinegar or nail polish.

A starter that lives in the fridge wants one or two wake-up feeds before pizza day. Using it cold and sluggish won’t ruin anything — it will just ferment slower than the math expects, so the schedule drifts late. When in doubt, watch the dough, not the clock: doubled, jiggly, sweet-smelling means ready.

The honest answer: change the yeast type in the calculator and let it re-weigh everything — the dose, and the flour-and-water accounting above, both change.

For napkin math, the model’s ratios are constant: starter ≈ 25× a fresh-yeast dose, or 75× an instant-dry dose, for the same plan. Just remember the starter brings half its weight in flour and half in water — subtract those from the recipe’s adds or the dough ends up wetter than written.

Sourdough’s bacteria make lactic and acetic acid alongside the rise. In moderation that’s the whole point: depth, a gentle tang, better keeping, and a crust that browns beautifully.

Push the ferment very long and very sour, though, and the acid starts working on the gluten itself — the dough turns slack, fragile, tears at stretching time. If that’s your experience, ferment cooler, shorten the warm hours, or feed the starter more often so less acid comes along in the dose. Sour is seasoning, not a victory condition.