Yeast to Sourdough Converter

Swapping packet yeast for a starter

You have a bread recipe you love, written for dried yeast, and a jar of starter that needs a job. Swapping one for the other is not as simple as leaving out the yeast and adding a scoop of starter, because a starter is itself flour and water. Add it on top of the recipe and the dough ends up wetter and heavier than intended.

This converter does the rebalancing for you. It works both ways: turning a yeasted recipe into a sourdough one, and turning a sourdough recipe into a same-day yeasted version when you need bread faster.

Keeping the dough the same

The goal is that the finished dough has the same total flour, the same total water and the same salt as before. The texture, hydration and seasoning then stay recognisable. In the sourdough direction, the calculator works out how much starter to use, then subtracts what the starter contains from what you add to the bowl. In the other direction, the flour and water that were inside the starter go back into the bowl, and yeast takes over the rising.

Step by step

1. Choose a Direction: Yeast to sourdough or Sourdough to yeast.
2. Under Your recipe, enter Flour, Water and Salt. Flour means what goes into the bowl, not counting any starter.
3. Enter your Starter hydration; one that gets matching weights of flour and water at each feed is 100%.
4. Going to sourdough, choose Starter to use under Sourdough version. Between 15 and 25% of total flour suits most loaves.
5. Going to yeast, enter Starter in the recipe, then pick a Yeast type and Yeast, as instant under Yeasted version.

The results list the new recipe along with Total flour, Hydration and, in the sourdough direction, Flour prefermented in starter.

Converting a sandwich loaf

The recipe calls for 600 g flour, 420 g water, 12 g salt and a packet of instant yeast. Choose Yeast to sourdough with Starter to use at 20% and a 100% starter:

• Starter: 120 g
• Flour to add: 540 g
• Water to add: 360 g
• Salt: 12 g
• Total flour: 600 g
• Hydration: 70%
• Flour prefermented in starter: 10%

The 120 g of starter carries 60 g of flour and 60 g of water, so the bowl gets 60 g less of each. Total flour stays at 600 g and hydration at 70%, exactly as in the original. The yeast is simply left out.

Prefer a slower, milder rise? Drop Starter to use to 15%. The starter becomes 90 g, flour to add 555 g and water to add 375 g.

Going the other way, a sourdough recipe with 450 g flour, 325 g water, 100 g starter and 9 g salt becomes Flour 500 g, Water 375 g, Salt 9 g and Instant yeast 5 g, about 1.61 tsp, at 75% hydration. Pick active dry instead and the yeast line reads 6 g.

Timing is the part that changes

Commercial yeast is bred for speed. A starter holds far fewer yeast cells and shares the dough with bacteria, so the rise is slower and the flavour tangier. Expect the sourdough version to need several hours of bulk fermentation where the yeasted recipe needed one or two. The bulk fermentation time estimator gives a guide for your dough temperature, and the sourdough schedule planner maps the whole day.

Tips for a smooth switch

• Use starter at its peak. A sluggish starter makes the slow rise even slower.
• Build what you need. The levain builder makes 120 g of ripe levain with a little extra for the jar.
• Keep enrichments as they are. Butter, sugar, eggs and milk stay the same; only flour, water and leavening move.
• Enriched doughs rise more slowly with starter. Sugar and fat hold the culture back, so allow even more time.
• Unusual starter? Confirm the real hydration. The sourdough hydration calculator shows the effect of a stiff or very wet culture.

Quick answers

Can I keep a little yeast in the sourdough version?

Some bakers add a pinch for insurance. It speeds things up and softens the sour flavour, but the dough is then no longer a pure sourdough, and the timings here no longer apply.

Why do I need the starter’s hydration?

At 100% hydration the starter splits evenly into flour and water, while a stiff 60% starter leans heavily towards flour. The split decides how much to take off the flour and water in the bowl.

What if the calculator says the starter is too wet?

That happens with low-hydration recipes and a lot of starter: the starter alone brings more water than the dough is allowed. Use less starter or a stiffer one.

Does the yeast amount in the reverse direction suit every bread?

About 1% instant yeast is a common starting point for a same-day loaf. Rich doughs often use more, and long cold rises much less. Adjust it to fit your day.