To convert a yeasted recipe to sourdough, replace 1 packet (2.25 tsp / 7 g) of active dry or instant yeast with 100 g of ripe, 100%-hydration sourdough starter, then subtract 50 g of flour and 50 g of water from the recipe to compensate for the flour and water already inside the starter.
This substitution is proportional: 100 g of 100%-hydration starter contains 50 g flour and 50 g water. If you use more starter, subtract proportionally more flour and water.
The Conversion Formula
Step 1. Decide how much starter to use. Most recipes work well with 15–20% starter relative to flour weight.
Step 2. Since 100%-hydration starter is half flour and half water by weight:
- Starter flour = starter weight ÷ 2
- Starter water = starter weight ÷ 2
Step 3. Subtract starter flour from recipe flour, and starter water from recipe water.
Step 4. Eliminate the commercial yeast entirely.
Step 5. Add salt last after mixing starter into the dough.
Worked Example: Basic Sandwich Loaf Conversion
Original yeasted recipe:
| Ingredient | Original |
|---|---|
| Bread flour | 500 g |
| Water | 325 g |
| Salt | 10 g |
| Instant yeast | 4 g |
Target: use 100 g of ripe sourdough starter (replacing the yeast).
Starter contains: 50 g flour + 50 g water.
Converted recipe:
| Ingredient | Converted |
|---|---|
| Bread flour | 500 − 50 = 450 g |
| Water | 325 − 50 = 275 g |
| Salt | 10 g (unchanged) |
| Ripe starter | 100 g |
| Instant yeast | (eliminated) |
Total flour remains 500 g (450 g recipe flour + 50 g flour in starter). Hydration and salt percentage stay the same.
How Fermentation Time Changes
Commercial yeast at room temperature: first rise in 1–2 hours. Sourdough at 75–78°F with 20% starter: bulk fermentation in 4–6 hours.
| Starter % | Bulk time at 75°F | Flavor |
|---|---|---|
| 10% | 7–10 hours | Tangy, complex |
| 20% | 4–6 hours | Mildly tangy |
| 30% | 2–4 hours | Mild, quick |
Shape when dough has risen 50–75% and passes the jiggle test. Proofing after shaping takes another 1–3 hours at room temperature, or 8–16 hours cold in the refrigerator. See sourdough schedule examples for complete timelines.
Adjusting for Different Hydration Starters
The math above assumes a 100%-hydration starter (equal parts flour and water by weight). If your starter is a different hydration, adjust accordingly:
- Stiff starter at 50% hydration: 100 g of starter contains about 67 g flour and 33 g water. Subtract 67 g flour and 33 g water from the recipe.
- Very wet starter at 125% hydration: 100 g contains about 44 g flour and 56 g water. Subtract those amounts.
Most home bakers keep 100%-hydration starters. If you are unsure, check how you feed yours: 1:1 flour-to-water by weight = 100% hydration.
The Hybrid Method: Starter and a Small Amount of Yeast
If your starter is not at full strength, or you want sourdough flavor with more predictable timing, use a hybrid approach: add a small amount of commercial yeast alongside your starter. The starter contributes flavor and acidity; the yeast provides reliable leavening power.
For 500 g flour, a common hybrid formula:
- 100 g active starter (provides flavor and some lift)
- 0.5–2 g instant yeast (provides reliability and faster rise)
- Subtract 50 g flour and 50 g water from the recipe for the starter as usual
The result behaves more like a yeasted dough in timing (3–4 hours rather than 6–10) but develops some sourdough tang. This is especially useful for enriched doughs or when the kitchen is cold.
Converting Back: Sourdough to Yeast
To reverse-convert a sourdough recipe to commercial yeast:
- Remove the starter from the ingredient list.
- Add back the flour and water that the starter contained (starter weight ÷ 2 each).
- Add commercial yeast: for same-day baking with 500 g flour, use 5–7 g instant yeast; for an overnight slow-rise, use 1–2 g.
- Expect the first rise to take 1–2 hours instead of 4–10 hours.
The flavor will be milder — no sourdough tang — and the bread will have a softer crust. You can add a tablespoon of apple cider vinegar to approximate some of the tang if desired.
Adjusting Enriched Doughs
Recipes with butter, eggs, or sugar rise more slowly because fat coats the yeast and sugar competes for water. For these:
- Use 20–30% starter to compensate for the slower environment
- Expect bulk fermentation to take 5–8 hours at 75°F
- Cold-retarding the shaped dough overnight is especially effective for sweet rolls and brioche — the slow, cold proof develops flavor without over-fermentation
What Stays the Same
- Shaping technique: identical to the original yeasted method
- Baking temperature and time: no change needed
- Oven temperature and pan: same as original recipe
What Changes
- Total rise time (longer — 4–12 hours instead of 1–2 hours)
- Flavor (slightly tangy even with same-day bake)
- Timing flexibility (more forgiving — dough can sit in the fridge for hours without collapsing)
- Leavening source (wild yeast and bacteria from your starter)
Troubleshooting
| Problem | Likely cause | Fix |
|---|---|---|
| Dough not rising after 8 hours | Starter not at peak | Feed starter 4–8 hours before mixing; it should double and dome |
| Dough too wet and sticky | Forgot to subtract starter’s water from recipe | Recalculate; add extra flour to adjust |
| Bread tastes like bland yeasted bread, not tangy | Used starter too young or converted too quickly | Extend bulk fermentation 2–4 hours; cold-retard overnight for more tang |
| Bread collapsed or has large holes | Over-fermented | Shorten bulk; shape at 50% rise, not 100% |
| Dough dense and won’t pass float test | Starter not ready | Starter should float in water when at peak; wait for this stage |
For how to maintain a healthy starter at peak before each bake, see sourdough starter feeding ratios.