Yeast to Sourdough Converter

Why convert to sourdough?

Sourdough starter is wild yeast and lactic acid bacteria — two organisms that work together to ferment bread slowly and develop complex flavour. Compared to commercial yeast, sourdough is slower, more forgiving, and produces a bread with tangier flavour, better texture, and longer shelf life.

The catch: fermentation timing is different. A recipe designed for commercial yeast assumes a predictable, fast rise. Replace it with starter and you need to adjust fermentation time (usually longer), starter percentage (the leavening power is lower), and sometimes hydration (starter adds liquid to the dough). This calculator handles all of it.

You don't need a separate sourdough recipe collection. Convert your trusted recipes on the fly. Once you understand how the conversions work, you can adapt any yeast bread to sourdough and get consistent results.

How the conversion works

The converter takes your yeast recipe and adjusts three things. It removes yeast and replaces it with sourdough starter (usually 15–25% of flour weight). It accounts for the flour and water inside that starter by adjusting your added water. It extends fermentation time for the slower activity of wild yeast.

Start by entering your original yeast recipe: flour weight, water percentage or weight, salt, sugar, fat, and yeast amount. Choose your starter hydration (100% is standard) and your desired starter percentage (20% is a good starting point; adjust based on fermentation time preferences). The calculator returns your converted recipe.

The converted recipe accounts for flour and water inside your starter. Your final dough hydration stays close to the original. If the original was 65% hydration, your sourdough conversion will be roughly 65% too. Salt, sugar, and fat amounts stay the same. These don't need adjustment between yeast and sourdough recipes.

Starter percentage and fermentation

The amount of starter you use directly controls fermentation speed. Less starter = slower fermentation = more time to develop flavour and sour tang. More starter = faster fermentation = shorter timeline but less sour, less complex character.

For a room-temperature overnight bake (8–12 hours at 20–22°C), use 15–20% starter. This is the sweet spot for most home bakers: slow enough to build flavour, fast enough to fit a normal baking schedule. For a long, cold fermentation (overnight fridge, then room temperature in the morning), you can drop to 10–15% starter and let the cold work for you.

If you want a quick sourdough bake (same-day, 4–6 hours), use 25–30% starter and keep the kitchen warm. Your dough ferments faster and still develops good flavour, though the sourness will be subtle. Temperature matters a lot: 5°C cooler can double the fermentation time, so adjust expectations based on your kitchen conditions.

Why hydration changes

When you replace yeast with starter, you're adding both yeast and water to the dough. Starter is typically 100% hydration — half flour, half water by weight. So if you add 200g of 100% hydration starter, you're adding 100g flour and 100g water.

To keep the final dough hydration the same, the calculator reduces your added water to compensate. If your original recipe called for 650g water and you're adding 200g of starter (100g water inside), you'd reduce the added water to 550g. Total water is still 650g, so your final hydration is unchanged.

The flour adjustment is automatic too. If you're adding 200g of starter (100g flour inside), the added flour from the starter counts toward your total flour percentage. This is why the converter needs to know your starter's hydration: looser starters contribute more water, stiffer starters contribute more flour.

Adjusting fermentation time

Sourdough ferments slower than commercial yeast, even at the same temperature. A dough that takes 4 hours with yeast might take 8–12 hours with the same amount of sourdough starter. This is because wild yeast (the primary leavener in starter) is less potent by cell count than commercial yeast, though it produces more flavour compounds over the longer timeline.

The calculator estimates fermentation time by adjusting your starter percentage and temperature: higher starter percentage and warmer temperature = faster fermentation. Use these estimates as starting points. Watch the dough's volume (it should grow 50–75% during bulk for lean bread), feel for the jiggle and the texture, and adjust based on what you see. Visual cues always beat the timer.

If your starter is freshly fed (active and vigorous), fermentation will be at the faster end of the range. If your starter was fed 12+ hours ago and is sluggish, add 25–50% more time. Starter activity varies week to week based on flour and feeding schedule. Once you've baked the converted recipe once or twice, you'll dial in the timing for your particular starter and kitchen.

Cold fermentation for sourdough

The easiest way to manage sourdough timing is cold fermentation. Bulk ferment at room temperature for 4–6 hours, then refrigerate (4°C / 39°F) for 12–18 hours or longer. The cold dramatically slows fermentation, so you can bake whenever you want the next day without waking up early or watching the dough constantly.

Cold also develops more flavour. The long fermentation at low temperature gives more time for enzymatic breakdown and organic acid production, so your bread tastes more complex and sour. Many professional sourdough bakeries run 18–24 hour cold ferments as standard.

For cold fermentation, you can use the same starter percentage as a room-temperature bake — the bulk phase at room temperature is short, so less starter is needed. Shape after the short bulk, then refrigerate. The cold phase substitutes for the long room-temperature fermentation. This works beautifully for overnight bakes and is much more forgiving than a pure room-temperature timeline.

Frequently asked questions

How much sourdough starter replaces 1 teaspoon of instant yeast?

1 teaspoon of instant yeast (about 3.1g) is replaced by approximately 370g of active 100% hydration sourdough starter, or more practically, 15–20% starter by flour weight. In most cases, the starter percentage approach is more useful: a recipe with 500g flour would use 75–100g of active starter as a starting point. The conversion isn't purely weight-for-weight because sourdough ferments slower. You also need to add 8–12 hours of bulk fermentation time.

Do I need to change the water in a recipe when converting to sourdough?

Yes. Sourdough starter contains water (typically 50% at 100% hydration). When you add starter to a recipe, you're also adding water from inside the starter. To keep the same final dough hydration, reduce your added water by the amount of water inside the starter. For example: 200g of 100% hydration starter contributes 100g water, so reduce your recipe's added water by 100g. This calculator does this adjustment automatically.

Will my converted sourdough recipe taste the same as the yeast version?

No. And that's the point. Sourdough fermentation produces lactic and acetic acids that add tanginess, complexity, and depth that commercial yeast recipes lack. The texture is also different: sourdough crumb tends to be chewier and more open, with better keeping quality (stays fresh 3–4 days vs. 1–2 days for commercial yeast bread). If you want subtle sourdough flavour, use a short fermentation with more starter. For pronounced tang, use less starter and ferment longer.

Can I convert any yeast recipe to sourdough?

Most lean bread recipes (flour, water, salt, yeast) convert directly. Enriched recipes (brioche, cinnamon rolls, milk bread) also convert well, though enriched doughs ferment more slowly with sourdough because fat and sugar inhibit yeast activity. Use a higher starter percentage or longer fermentation time. Recipes that rely on very fast rising (quick breads with baking powder, or no-knead recipes timed to 2 hours) aren't good candidates for sourdough conversion.

How long does sourdough take compared to a yeast recipe?

A typical commercial yeast recipe takes 2–4 hours total. The sourdough equivalent takes 8–16 hours at room temperature, or up to 24 hours with a cold proof. The extra time isn't active work. Most of it is hands-off fermentation. The easiest approach: mix in the evening, bulk ferment at room temperature for 4–6 hours, shape, refrigerate overnight, bake the next morning. Total hands-on time is similar; the clock time is longer but fits naturally around a normal day.