Replacing 120g High-Hydration (125%) Sourdough Starter with Instant or Active Dry Yeast
Liquid-heavy starter reverse conversion: adding back +66.7g water and +53.3g flour when swapping 120g (125%) starter for yeast.
The arithmetic runs in reverse. A starter at 125% hydration divides into 120 ÷ (1 + 1.25) of flour and the remainder as water — here 53.3g and 66.7g. Add both back to the 450g + 315g base and the batch is whole again at 503.3g / 381.7g, ready for 7g of commercial yeast instead of a levain.
- Add Back Flour
- +53.3gReplaces flour inside 120g (125%) starter
- Add Back Water
- +66.7gReplaces water inside 120g (125%) starter
- Instant Yeast (2-Hr Rise)
- 7g (2.3 tsp)For 503.3g total flour batch
- Preserved Hydration
- 75.8%381.7g W / 503.3g F
Yeast Replacement Matrix for 120g Starter (125% Hydration) Across 3 Fermentation Speeds
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 |
|---|---|---|---|---|
| [Exact Target]: 100g starter at 125% | instant 6.9g | active dry 8.7g | fresh 20.8g | bake 1.5 – 2.0 hours warm bulk rise |
| Alt Row A: 120g starter at 125% | instant 3.5g | active dry 4.4g | fresh 10.6g | bake 3.5 – 4.5 hours slow room-temp rise |
| Alt Row B: 140g starter at 125% | instant 1.3g | active dry 1.6g | fresh 3.8g | bake 12 – 18 hours cold fermentation (39°f / 4°c) |
| Alt Row C: 110g starter at 125% | instant 7g | active dry 8.7g | fresh 21g | bake 1.5 – 2.0 hours warm bulk rise |
| Alt Row D: 130g starter at 125% | instant 3.6g | active dry 4.4g | fresh 10.7g | 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 +53.3g baseline.
Why 120g of 125% High-Hydration Starter Requires Asymmetric Water Restoration
The three yeast formats are not interchangeable at equal weight. Active Dry Yeast is a live but partly dehydrated culture carrying roughly 80% of the potency per gram of instant yeast, while fresh compressed cake yeast is only about a third, so 7g of instant corresponds to 8.8g of active dry and 21g of fresh.
Crust colour is a tell. A levain dough browns more slowly because its sugars are already partly consumed, so a converted dough reaches a deeper, faster colour at the same temperature and often benefits from a slightly cooler oven.
Step-by-Step Reverse Conversion Protocol (120g @ 125%)
- Audit the Original Formula: Confirm the recipe's yeast was the only leavening, and that the 120g of 125% starter was the sole source of the 53.3g of hidden flour.
- Rebuild at Full Scale: The batch is now 503.3g flour and 381.7g liquid — the same numbers as before, minus the starter.
- Dose for the Schedule You Want: 7g (2.3 tsp) of instant yeast for a 1.5 – 2.0 hours warm bulk rise; use about a fifth of that for a cold overnight ferment.
- Bake and Compare: The crumb will be lighter and less acid-forward, but the volume and crust colour should be close to the levain original.
Common Scaling & Troubleshooting Questions (+53.3g)
Does the converted dough keep the same dough weight?
Almost — the 120 grams of starter is replaced by the 7g of yeast plus the 53.3g of flour and 66.7g of water you put back, which is a slightly different total.
Can I use Active Dry Yeast instead of Instant Yeast to replace 120g starter?
Yes — multiply the 7g Instant Yeast weight by 1.25x and dissolve it in warm (100°F / 38°C) water from your 66.7g water addition.
Can I convert a dough that also contains a poolish or preferment?
Yes, but count the preferment's yeast separately and subtract it from the 7g, otherwise the 503.3g dough will over-proof.