Convert 120g Sourdough Starter (80% Hydration) to Commercial Yeast
How to remove 120g of 80% hydration levain from any sourdough recipe by restoring +66.7g flour and +53.3g water.
Why bother converting back at all? Three reasons. You need a predictable two-hour rise for a schedule; you want the cleaner flavour of a commercial-yeast crumb; or you have 120g of starter in the jar you would rather not waste. The cost is that you lose the acid complexity, so season the dough with the recipe's own aromatics.
- Add Back Flour
- +66.7gReplaces flour inside 120g (80%) starter
- Add Back Water
- +53.3gReplaces water inside 120g (80%) starter
- Instant Yeast (2-Hr Rise)
- 7.2g (2.3 tsp)For 516.7g total flour batch
- Preserved Hydration
- 71.3%368.3g W / 516.7g F
Yeast Replacement Matrix for 120g Starter (80% Hydration) Across 3 Fermentation Speeds
Neighbouring starter weights are included so you can scale the swap up or down from the same base formula.
| Fermentation Speed | Instant Yeast (g / tsp) | Active Dry Yeast (g / tsp) | Fresh Yeast (g) | Add Back Flour & Water |
|---|---|---|---|---|
| Line 100g / 80% [Exact Target] | 7.1g IDY (2.3 tsp) | 8.8g ADY (2.9 tsp) | 21.2g cake yeast | 1.5 – 2.0 hours warm bulk rise |
| Line 120g / 80% Alt Row A | 3.6g IDY (1.2 tsp) | 4.5g ADY (1.5 tsp) | 10.9g cake yeast | 3.5 – 4.5 hours slow room-temp rise |
| Line 140g / 80% Alt Row B | 1.3g IDY (0.4 tsp) | 1.6g ADY (0.5 tsp) | 4g cake yeast | 12 – 18 hours cold fermentation (39°F / 4°C) |
| Line 110g / 80% Alt Row C | 7.2g IDY (2.3 tsp) | 8.9g ADY (2.9 tsp) | 21.5g cake yeast | 1.5 – 2.0 hours warm bulk rise |
| Line 130g / 80% Alt Row D | 3.7g IDY (1.2 tsp) | 4.6g ADY (1.5 tsp) | 11g cake yeast | 3.5 – 4.5 hours slow room-temp rise |
Dynamic Stoichiometric Workbench (+66.7g)
Test custom loaf weights or alternative fermentation schedules directly against the +53.3g benchmark above.
Decomposing 120g of 80% Hydration Starter: Flour + Water Conservation
Yeast dose scales with total flour, not with the amount of levain you removed. On a 450g base that becomes 516.7g of system flour, the 1.4% instant-yeast rule for a two-hour rise lands on 7.2g, and every hour you extend the schedule cuts that figure.
Watch the oven spring rather than the mixing. With 7.2g 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 (120g @ 80%)
- Weigh the Restoration (66.7g + 53.3g): Set out the flour and water that were hiding inside the 120 g of 80% starter before you do anything else.
- Build the Dough (516.7g F / 368.3g W): Combine them with the original 450g and 315g, then add 2% salt and 7.2g 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.
Key Baker's Math Questions (Add Back Flour: +66.7g)
Does converting to yeast change the fermentation time?
Dramatically. A levain dough on this 516.7g base would need many hours; the 7.2g of commercial yeast gives you a 1.5 – 2.0 hours warm bulk rise.
Is 120 g of 80% 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 66.7g / 53.3g restoration is larger on the flour side and smaller on the water side.
Can I scale the conversion to a different flour weight?
Yes. The yeast dose is a percentage of total flour, so on a larger batch multiply 7.2g by the ratio of the new flour weight to 516.7g.