How to Convert a Yeast Recipe to Sourdough

Most lean bread recipes written for instant or active dry yeast can be made with a sourdough starter instead. The swap is not one-for-one, though. A starter is itself flour and water, so it changes the dough's totals, and wild yeast works far more slowly than a packet, so every rise stretches from an hour or two to several hours.

This guide walks through the arithmetic with a worked example, explains how to plan the longer timeline, and covers the doughs that need extra care: enriched breads heavy with butter, sugar and eggs, which slow a starter down even further.

Why the swap needs math

A typical 100 percent hydration starter is equal weights of flour and water. Drop 100 g of it into a recipe and you have quietly added 50 g of flour and 50 g of water. In a small loaf that is enough to change how the dough handles, so the clean approach is to take those amounts back out of the main flour and water.

Salt is calculated on total flour, including the flour in the starter. Most lean breads sit near 2 percent salt, so if the original recipe used 10 g of salt for 500 g of flour, keep 10 g; the total flour has not changed, it has only moved partly into the starter.

A worked conversion

Take a simple yeasted loaf: 500 g bread flour, 350 g water (70 percent hydration), 10 g salt and 7 g instant yeast. We will use 100 g of ripe 100 percent hydration starter, which is 20 percent of the flour.

That starter holds 50 g flour and 50 g water. Subtract them: the main dough now takes 450 g flour and 300 g water. Add the 10 g salt and leave out the yeast entirely. Totals are still 500 g flour, 350 g water and 70 percent hydration, so the dough should feel the way the original author intended.

• Original: 500 g flour, 350 g water, 10 g salt, 7 g instant yeast
• Starter: 100 g (50 g flour + 50 g water)
• Converted dough: 450 g flour, 300 g water, 10 g salt, 100 g starter
• If your starter is kept stiffer, at 50 to 60 percent hydration, recalculate the split using its actual flour and water weights

Planning the longer timeline

Wild yeast and bacteria take longer to raise dough than a packet of instant yeast. At around 24°C (75°F), a dough with 20 percent starter usually needs 4 to 6 hours of bulk fermentation, followed by 1 to 3 hours of final proof at room temperature or an overnight proof in the refrigerator.

Temperature moves these numbers more than anything else. A cool kitchen at 20°C (68°F) can push bulk past 8 hours; a warm one at 27°C (80°F) can finish in under 4. If you need the dough to wait, reduce the starter to 10 percent and let it run overnight on the counter, or shape it and retard it in the fridge for 8 to 16 hours.

Reading the dough instead of the recipe

The original recipe's instruction to let the dough double in an hour no longer applies. For lean sourdough, many bakers end bulk when the dough has grown by about half to three-quarters, feels airy and jiggly, shows bubbles on the sides of a clear container and has a slightly domed surface.

Keep the original shaping, scoring and baking temperatures. Those steps depend on the type of loaf, not on the leavening, so a sandwich loaf still bakes in its pan and a baguette still wants steam. Bake times are usually unchanged, though sourdough crusts can color a little faster because of the extra sugars freed during the longer ferment.

Enriched doughs and special cases

Butter, sugar, eggs and milk all slow fermentation. For brioche, challah or cinnamon roll dough, raise the starter to 25 to 30 percent of flour and keep the dough warm, around 26°C (79°F). Even then, the first rise can take 6 hours or more, and the final proof may be slow.

Some bakers keep a tiny amount of instant yeast, about 1 g per 500 g flour, alongside the starter in rich doughs. This hybrid keeps the schedule manageable while the starter adds flavor and keeping quality. It is a reasonable choice when the aim is a reliable bake rather than a purely wild-fermented one.

• Recipes leavened partly by baking soda or powder are not good candidates for full conversion
• Whole grain doughs ferment faster; check them earlier
• A sluggish starter will make every conversion fail; make sure it doubles within 4 to 8 hours of feeding first

Common questions

Can I just add starter on top of the recipe without adjusting anything?

You can, and many breads will still work, but the dough will be wetter and slightly larger than intended. In a small recipe the extra water can make shaping harder. Subtracting the starter's flour and water keeps the result predictable.

Will a converted loaf taste sour?

Usually mildly. Sourness depends on the starter, the length of fermentation and temperature. A short, warm bulk with a young starter tastes gentle; a long cold retard and a starter fed with whole grain rye taste sharper.

Should I use discard instead of active starter?

Not for leavening. Unfed discard has little rising power left. Use starter at its peak, a few hours after feeding when it has roughly doubled and smells pleasantly sour, not sharp or like nail polish.