How to Convert 40g Stiff Sourdough Starter (50% Hydration) to Commercial Yeast
Restoring +26.7g flour and +13.3g water when replacing 40g of 50% stiff levain with dry or fresh yeast.
Think of the swap as a bookkeeping exercise, not a recipe change. 40 g of 50% starter is not 40 g of nothing — it is 26.7g of flour and 13.3g of water that you are about to delete. Put them back, and the dough returns to 476.7g flour and 328.3g water at 68.9% hydration, now leavened by 6.7g of instant yeast for a 1.5 – 2.0 hours warm bulk rise.
- Add Back Flour
- +26.7gReplaces flour inside 40g (50%) starter
- Add Back Water
- +13.3gReplaces water inside 40g (50%) starter
- Instant Yeast (2-Hr Rise)
- 6.7g (2.2 tsp)For 476.7g total flour batch
- Preserved Hydration
- 68.9%328.3g W / 476.7g F
Yeast Replacement Matrix for 40g Starter (50% Hydration) Across 3 Fermentation Speeds
Calculated on a 450g main flour + 26.7g restored starter flour (476.7g total flour) batch.
| Target Fermentation Schedule | Instant Dry Yeast (IDY) | Active Dry Yeast (ADY) | Fresh Compressed Yeast | Required Dough Restoration |
|---|---|---|---|---|
| Line 30g / 50% [Your Batch] | 6.6g IDY (2.1 tsp) | 8.2g ADY (2.7 tsp) | 19.7g cake yeast | 1.5 – 2.0 hours warm bulk rise |
| Line 60g / 50% Scaled Down | 3.4g IDY (1.1 tsp) | 4.3g ADY (1.4 tsp) | 10.3g cake yeast | 3.5 – 4.5 hours slow room-temp rise |
| Line 40g / 50% Scaled Up | 1.2g IDY (0.4 tsp) | 1.5g ADY (0.5 tsp) | 3.6g cake yeast | 12 – 18 hours cold fermentation (39°F / 4°C) |
| Line 20g / 50% Trimmed | 6.5g IDY (2.1 tsp) | 8.1g ADY (2.6 tsp) | 19.5g cake yeast | 1.5 – 2.0 hours warm bulk rise |
| Line 50g / 50% Expanded | 3.4g IDY (1.1 tsp) | 4.2g ADY (1.4 tsp) | 10.2g cake yeast | 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 +26.7g baseline.
Decomposing 40g of 50% Stiff Levain: High-Flour Mass Conservation
The hydration of the original starter is the single biggest variable in this conversion. At 50% the 40g carries 26.7g of flour; at 50% the same weight would carry 27g, which is a completely different deduction and a completely different batch.
Shelf life shortens. The 68.9% hydration dough leavened by 6.7g of yeast stales faster than the levain version, because there is no residual acid to slow starch retrogradation.
Step-by-Step Reverse Conversion Protocol (40g @ 50%)
- Dissolve the Yeast: Bloom 6.7g of instant yeast in a little of the 13.3g restored water at 100°F (38°C) so it disperses evenly through the 476.7g of flour.
- Combine Dry and Wet: Add the 26.7g of restored flour to the original flour, pour in the 328.3g of water and the yeast slurry, and mix until no dry flour remains.
- Add Salt Last: Work 2% salt into the dough and continue mixing until a windowpane forms.
- Single Bulk, No Folds Needed: Let the dough rise undisturbed for 1.5 – 2.0 hours warm bulk rise, then shape, prove briefly and bake.
Common Scaling & Troubleshooting Questions (+26.7g)
Is this conversion useful for pizza or focaccia dough?
Very. A commercial-yeast dough on 476.7g of flour with 6.7g of yeast rises predictably, which suits a same-day pizza schedule, and the cold-ferment option works for overnight pizza too.
Does the converted dough keep the same dough weight?
Almost — the 40g of starter is replaced by the 6.7g of yeast plus the 26.7g of grain and 13.3g of water you put back, which is a slightly different total.
How much instant yeast replaces 40g of 50% sourdough starter?
For a standard 1.5–2 hour rise on a 476.7g total flour loaf, use 6.7g (2.2 tsp) of Instant Dry Yeast and add back 26.7g flour + 13.3g water.