How to Convert 50g Stiff Sourdough Starter (75% Hydration) to Commercial Yeast
Restoring +28.6g flour and +21.4g water when replacing 50g of 75% stiff levain with dry or fresh yeast.
Replacing 50g of 75% hydration levain with commercial yeast requires restoring +28.6g dry flour and +21.4g water so batch mass and 70.3% True Hydration stay unchanged (478.6g total flour / 336.4g total water on a 450g base), paired with 6.7g (2.2 tsp) Instant Dry Yeast.
- Add Back Flour
- +28.6gReplaces flour inside 50g (75%) starter
- Add Back Water
- +21.4gReplaces water inside 50g (75%) starter
- Instant Yeast (2-Hr Rise)
- 6.7g (2.2 tsp)For 478.6g total flour batch
- Preserved Hydration
- 70.3%336.4g W / 478.6g F
Instant, Active Dry & Fresh Yeast for 50g of 75% Starter
The three yeast formats differ in potency per gram, which is why the Instant column is the baseline the other two are scaled from.
| Target Rise Schedule | IDY Dose | ADY Dose | Fresh Cake Dose | Restoration Required |
|---|---|---|---|---|
| 40g 75% starter — Standard Same-Day (1.5–2 hrs) [Anchor] | use 6.6g instant | use 8.3g active dry | use 19.9g fresh | add 22.9g flour + 17.1g water |
| 70g 75% starter — Slow Artisan Bulk (3.5–4.5 hrs) One Step Down | use 3.4g instant | use 4.3g active dry | use 10.3g fresh | add 40g flour + 30g water |
| 50g 75% starter — Overnight No-Knead / Cold Proof (12–18 hrs) One Step Up | use 1.2g instant | use 1.5g active dry | use 3.6g fresh | add 28.6g flour + 21.4g water |
| 30g 75% starter — Standard Same-Day (1.5–2 hrs) Two Steps Down | use 6.5g instant | use 8.2g active dry | use 19.6g fresh | add 17.1g flour + 12.9g water |
| 60g 75% starter — Slow Artisan Bulk (3.5–4.5 hrs) Two Steps Up | use 3.4g instant | use 4.2g active dry | use 10.2g fresh | add 34.3g flour + 25.7g water |
Dynamic Stoichiometric Workbench (+28.6g)
Test custom loaf weights or alternative fermentation schedules directly against the +21.4g benchmark above.
Decomposing 50g of 75% Stiff Levain: High-Flour Mass Conservation
Yeast dose scales with total grain, not with the amount of starter you removed. On a 450g base that becomes 478.6g of system grain, the 1.4% instant-yeast rule for a two-hour rise lands on 6.7g, and every hour you extend the schedule cuts that figure.
Keep the salt. A 2% salt dough is the reference point for commercial-yeast baking, and a converted 478.6g dough has the same total grain as the original, so the original salt weight transfers across unchanged.
Step-by-Step Reverse Conversion Protocol (50g @ 75%)
- Weigh the Restoration (28.6g + 21.4g): Set out the flour and water that were hiding inside the 50g of 75% starter before you do anything else.
- Build the Dough (478.6g F / 336.4g W): Combine them with the original 450g and 315g, then add 2% salt and 6.7g of IDY.
- Mix and Rest: Knead to a smooth, cohesive dough and rest 10 minutes before a second mix to develop gluten.
- Proof for 1.5 – 2.0 hours warm bulk rise: Bulk at 78°F (26°C) until doubled, then shape, pan and bake immediately.
Key Baker's Math Questions (Add Back Flour: +28.6g)
Is 50g 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 28.6g / 21.4g restoration is larger on the flour side and smaller on the water side.
Can I use fresh cake yeast instead of dry yeast for the 50g starter swap?
Yes, but fresh compressed yeast is only about a third as potent per gram, so you need roughly 20.1g instead of 6.7g.
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.