How to Convert 300g Stiff Sourdough Starter (75% Hydration) to Commercial Yeast
Restoring +171.4g flour and +128.6g water when replacing 300g of 75% stiff levain with dry or fresh yeast.
Converting 300g of 75% starter to yeast in one line: restore 171.4g of flour and 128.6g of water to the main dough, yielding 621.4g of flour and 443.6g of liquid at 71.4% true hydration, then dose 8.7g (2.8 tsp) of instant yeast for a 1.5 – 2.0 hours warm bulk rise.
- Add Back Flour
- +171.4gReplaces flour inside 300g (75%) starter
- Add Back Water
- +128.6gReplaces water inside 300g (75%) starter
- Instant Yeast (2-Hr Rise)
- 8.7g (2.8 tsp)For 621.4g total flour batch
- Preserved Hydration
- 71.4%443.6g W / 621.4g F
Gram Weights for Replacing 300g of 75% Hydration 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 |
|---|---|---|---|---|
| Standard Same-Day (1.5–2 hrs) — 300g (75%) [Anchor] | IDY 8.7g / 2.8 tsp | ADY 10.9g / 3.5 tsp | fresh 26.1g | restore 171.4g + 128.6g |
| Slow Artisan Bulk (3.5–4.5 hrs) — 290g (75%) One Step Down | IDY 4.3g / 1.4 tsp | ADY 5.4g / 1.7 tsp | fresh 12.9g | restore 165.7g + 124.3g |
| Overnight No-Knead / Cold Proof (12–18 hrs) — 310g (75%) One Step Up | IDY 1.6g / 0.5 tsp | ADY 2g / 0.6 tsp | fresh 4.7g | restore 177.1g + 132.9g |
| Standard Same-Day (1.5–2 hrs) — 280g (75%) Two Steps Down | IDY 8.5g / 2.8 tsp | ADY 10.7g / 3.4 tsp | fresh 25.6g | restore 160g + 120g |
| Slow Artisan Bulk (3.5–4.5 hrs) — 320g (75%) Two Steps Up | IDY 4.4g / 1.4 tsp | ADY 5.5g / 1.8 tsp | fresh 13.3g | restore 182.9g + 137.1g |
Interactive Sourdough → Yeast Reverse Conversion Calculator
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Decomposing 300g of 75% Stiff Levain: High-Flour Mass Conservation
The hydration of the original starter is the single biggest variable in this conversion. At 75% the 300 g carries 171.4g of flour; at 50% the same weight would carry 200g, which is a completely different deduction and a completely different dough.
Keep the salt. A 2% salt dough is the reference point for commercial-yeast baking, and a converted 621.4g dough has the same total grain as the original, so the original salt weight transfers across unchanged.
Step-by-Step Reverse Conversion Protocol (300g @ 75%)
- Weigh the Restoration (171.4g + 128.6g): Set out the flour and water that were hiding inside the 300g of 75% starter before you do anything else.
- Build the Dough (621.4g F / 443.6g W): Combine them with the original 450g and 315g, then add 2% salt and 8.7g 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.
Frequently Asked Questions for This Sourdough → Yeast Reverse Conversion Spec
Why is my converted dough less extensible than the original?
Usually because the 128.6g of restored water was not added, leaving the dough drier and tighter, or because the levain's proteolysis was doing part of the gluten-softening work.
Can I use Active Dry Yeast instead of Instant Yeast to replace 300g starter?
Yes — multiply the 8.7g Instant Yeast weight by 1.25x and dissolve it in warm (100°F / 38°C) water from your 128.6g water addition.
How much instant yeast replaces 300g of 75% sourdough levain?
For a standard 1.5–2 hour rise on a 621.4g total flour loaf, use 8.7g (2.8 tsp) of Instant Dry Yeast and add back 171.4g flour + 128.6g water.