How to Convert 40g Stiff Sourdough Starter (75% Hydration) to Commercial Yeast
Restoring +22.9g flour and +17.1g water when replacing 40g of 75% stiff levain with dry or fresh yeast.
Converting 40g of 75% levain to yeast in one line: restore 22.9g of flour and 17.1g of water to the main dough, yielding 472.9g of flour and 332.1g of liquid at 70.2% true hydration, then dose 6.6g (2.1 tsp) of instant yeast for a 1.5 – 2.0 hours warm bulk rise.
- Add Back Flour
- +22.9gReplaces flour inside 40g (75%) starter
- Add Back Water
- +17.1gReplaces water inside 40g (75%) starter
- Instant Yeast (2-Hr Rise)
- 6.6g (2.1 tsp)For 472.9g total flour batch
- Preserved Hydration
- 70.2%332.1g W / 472.9g F
Reverse Conversion Chart: 40g Starter → Commercial Yeast
The schedule column is the one that changes your timeline: the same starter weight produces a very different ferment at each speed.
| Desired Schedule | IDY Weight | ADY Weight | Fresh Cake Weight | Flour / Water Restoration |
|---|---|---|---|---|
| Line 40g / 75% [Baseline] | 6.6g IDY (2.1 tsp) | 8.3g ADY (2.7 tsp) | 19.9g cake yeast | 1.5 – 2.0 hours warm bulk rise |
| Line 50g / 75% Smaller Batch | 3.4g IDY (1.1 tsp) | 4.2g ADY (1.4 tsp) | 10.1g cake yeast | 3.5 – 4.5 hours slow room-temp rise |
| Line 30g / 75% Larger Batch | 1.2g IDY (0.4 tsp) | 1.5g ADY (0.5 tsp) | 3.5g cake yeast | 12 – 18 hours cold fermentation (39°F / 4°C) |
| Line 60g / 75% Half Size | 6.8g IDY (2.2 tsp) | 8.5g ADY (2.7 tsp) | 20.3g cake yeast | 1.5 – 2.0 hours warm bulk rise |
| Line 20g / 75% Double Size | 3.2g IDY (1 tsp) | 4g ADY (1.3 tsp) | 9.7g cake yeast | 3.5 – 4.5 hours slow room-temp rise |
Live Parameter Solver for How to Convert 40g Stiff Sourdough Starter
Dial in custom baker's percentages and export your adjusted +22.9g formula for bake day.
Decomposing 40g of 75% Stiff Levain: High-Flour Mass Conservation
Salt interacts with the change. A levain dough was usually formulated for a 2% salt dough, and swapping in 6.6g of commercial yeast on the same 472.9g of flour keeps that salt level, which is a sensible place to leave the formula alone.
A practical test of a successful conversion: the batch should feel smooth rather than tacky after mixing, hold a windowpane, and reach the same volume in the oven as the original levain batch even though it got there in a fraction of the time.
Step-by-Step Reverse Conversion Protocol (40g @ 75%)
- Plan Around the Lost Complexity: Without a levain you lose the slow acid build, so if the 40g of 75% levain was there for flavour, add a little honey or malt and a spoonful of yoghurt.
- Restore the Mass: Return 22.9g of flour and 17.1g of water to the base recipe.
- Dose the Yeast: 6.6g (2.1 tsp) of instant, 8.3g of active dry, or 19.8g of fresh cake yeast.
- Ferment, Shape, Bake: Respect the 1.5 – 2.0 hours warm bulk rise schedule, and remember the 70.2% hydration is unchanged by the swap.
Cereal Chemistry & Bench Execution FAQs
Is 40g of 75% starter easier to replace than a wetter starter?
Easier in one sense: a stiffer starter carries more flour and less water per gram, so the 22.9g / 17.1g restoration is larger on the flour side and smaller on the water side.
How long should the converted dough bulk for at room temperature?
Plan on 1.5 – 2.0 hours warm bulk rise, then shape and bake immediately. There is no levain to justify a long slow bulk, and a commercial-yeast dough left longer simply over-proofs.
Will my converted dough taste different from the levain version?
Yes. The roughly 1g of residual acid inside 40g of starter was providing both flavour and tenderising, and commercial yeast replaces neither.