Hi William. Here’s the rule of thumb: sourdough starter is equal parts (by weight) flour and liquid. Say you want to use 1 cup (8 ounces) sourdough starter in your favorite sandwich bread recipe. If your recipe calls for 3 cups flour (approx. 12 ounces) and 1 cup water (8 ounces), reduce the flour in the recipe to 2 cups (8 ounces), and the water to 1/2 cup (4 ounces).This works pretty seamlessly for any recipe including both flour, and water or milk. Don’t substitute sourdough starter for eggs or oil or butter or honey or other liquids; it will change your recipe’s character. Happy Baking!

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