How to Convert 250g Stiff Sourdough Starter (75% Hydration) to Commercial Yeast
Restoring +142.9g flour and +107.1g water when replacing 250g of 75% stiff levain with dry or fresh yeast.
Think of the swap as a bookkeeping exercise, not a recipe change. 250 g of 75% starter is not 250 g of nothing — it is 142.9g of flour and 107.1g of water that you are about to delete. Put them back, and the dough returns to 592.9g flour and 422.1g water at 71.2% hydration, now leavened by 8.3g of instant yeast for a 1.5 – 2.0 hours warm bulk rise.
- Add Back Flour
- +142.9gReplaces flour inside 250g (75%) starter
- Add Back Water
- +107.1gReplaces water inside 250g (75%) starter
- Instant Yeast (2-Hr Rise)
- 8.3g (2.7 tsp)For 592.9g total flour batch
- Preserved Hydration
- 71.2%422.1g W / 592.9g F
Three Fermentation Schedules for a 250g (75%) Starter Swap
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 |
|---|---|---|---|---|
| [Exact Target]: 240g starter at 75% | instant 8.2g | active dry 10.3g | fresh 24.7g | bake 1.5 – 2.0 hours warm bulk rise |
| Alt Row A: 270g starter at 75% | instant 4.2g | active dry 5.3g | fresh 12.7g | bake 3.5 – 4.5 hours slow room-temp rise |
| Alt Row B: 250g starter at 75% | instant 1.5g | active dry 1.9g | fresh 4.4g | bake 12 – 18 hours cold fermentation (39°f / 4°c) |
| Alt Row C: 230g starter at 75% | instant 8.1g | active dry 10.2g | fresh 24.4g | bake 1.5 – 2.0 hours warm bulk rise |
| Alt Row D: 260g starter at 75% | instant 4.2g | active dry 5.2g | fresh 12.6g | bake 3.5 – 4.5 hours slow room-temp rise |
On-Bench Hydration & Fermentation Adjuster
Modify base flour mass, levain inoculation, or ambient kitchen temperature below to recalculate from this +142.9g baseline.
Decomposing 250g of 75% Stiff Levain: High-Flour Mass Conservation
By definition, a starter hydrated at 75% contains 100 parts flour and 75 parts water. Using Flour = 250 ÷ (1 + 0.75), your 250g of starter holds 142.9g of flour and 107.1g of water.
Watch the oven spring rather than the mixing. With 8.3g of commercial yeast the loaf will rise fast in the first 90 minutes, which means less time to develop a rounded shape and more chance of a flat crown if you shape too early.
Step-by-Step Reverse Conversion Protocol (250g @ 75%)
- Weigh the Restoration (142.9g + 107.1g): Set out the flour and water that were hiding inside the 250 grams of 75% starter before you do anything else.
- Build the Dough (592.9g F / 422.1g W): Combine them with the original 450g and 315g, then add 2% salt and 8.3g of instant yeast.
- 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.
Common Scaling & Troubleshooting Questions (+142.9g)
Can I convert a stiff 50% levain to yeast?
Yes, and the deduction is larger on the flour side: 250g at 50% hydration holds 167g flour and 83g water rather than the 142.9g / 107.1g of a 75% starter.
Can I convert a batch that also contains a poolish or preferment?
Yes, but count the preferment's yeast separately and subtract it from the 8.3g, otherwise the 592.9g batch will over-proof.
Does the converted dough keep the same dough weight?
Almost — the 250g of starter is replaced by the 8.3g of yeast plus the 142.9g of grain and 107.1g of water you put back, which is a slightly different total.