What's the approximate leavening power of sourdough starter?

I have a good starter going, and after being satisfied with it's performance in recipes written for starters, I'm now looking to start adapting the bread recipes I usually make to use the starter.

I feed it a 100% hydration, so subbing out equal portions (by weight) of water and flour for my starter is pretty straightforward, but I'm wondering about the yeast. I should be able to leave out the yeast and just rely on my starter to leaven, possibly allowing for more time, but I want to make sure I sub in approximately similar leavening power.

But how much starter should I use for each unit yeast? I read one source that says one cup of starter has about the "lift" as a quarter-ounce packet of yeast. I'm sure it varies some by colony, and will require some experimentation, but does anyone have a better starting point than that?



AntoniaJames June 13, 2016
I always do the substitution without reducing the yeast, and just keep an eye on the dough to prevent overproofing, typically doing both proof stages in the fridge to slow things down . . . . . . Luscious, tasty loaves, every time.

More info in the comments by Rivka and me, 4 years ago, on this buttermilk oatmeal bread recipe: https://food52.com/recipes/4022-buttermilk-oatmeal-bread

I updated it (had to, in a separate recipe, because the original was locked) to provide metric mass and volume measures, here: https://food52.com/recipes/40561-buttermilk-oatmeal-bread-updated

Also, a tip: you should limit the amount of starter used in substitution of the flour and liquid. I've done this quite a few times, and from experience find that you should substitute no more than about 25% of each of the flour and liquid. I usually do about 20%.

Finally, did you see this article? https://food52.com/blog/17140-preferments-and-how-to-adapt-any-bread-recipe-to-use-one

hardlikearmour June 12, 2016
I know this isn't the answer you're looking for, but my suggestion is to start with recipes developed for levain/sourdough starters. Once you get a feel for it you'll probably have better success with adapting your recipes. If you just want to give adaptation a go, start with 12-15% of the total flour in the recipe coming from the levain. Expect a 12-15 hour bulk fermentation before shaping the loaves, and a 3-4 hour proof. This is assuming standard room temp of 70-ish F for both stages. You could also go with a hybrid levain -- have 20% of the flour coming from the levain, and add 1/4-tsp instant yeast. Bulk ferment at room temperature about 5 hours, proof in the fridge 12-14 hours. (NB: percents are taken from bread recipes found in Flour, Water, Salt, Yeast by Ken Forkish. The breads in the book are of the no-knead variety and ~78% hydration so my guestimates for adapting your bread could be utterly off!)
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