Sourdough is well known for its ability to leaven breads. It can lend a lovely tang if you prefer, and it helps to make the grain more digestible by pre-digesting the fibers and anti-nutrients.
Those same benefits can be had for your quick bread recipes that normally call for baking soda or baking powder.
By replacing some of the flour and some of the liquid with a bit of sourdough starter, then fermenting the batter for at least 7 hours, you can achieve a delicious version of your favorite quick-bread recipes, like muffins, pancakes, or banana bread, with many of the benefits of a loaf of old-fashioned sourdough.
If a sourdough starter is kept at 100% hydration, assume that half of the weight is flour and the other half water. When converting a quick-bread recipe to sourdough, replace part of the flour and liquid in the recipe with the sourdough starter itself.
Furthermore, sourdough is acidic: it contains lactic and acetic acids that act on your recipe in the same way as the cultured dairy products that are often called for in a recipe.
A Recipe Conversion Example
A pancake recipe calls for 2 cups of flour and 2 cups of buttermilk. Combine 1¾ cups of flour, 1¾ cups of buttermilk, and ½ cup of sourdough starter. The sourdough starter replaces ¼ cup of the flour and ¼ cup of the buttermilk. In this example, milk could replace buttermilk, as well, because the sourdough starter contributes acidity as well as buttermilk.
Combine the mixture and ferment overnight on the counter at room temperature. The next morning add the rest of the recipe ingredients, including a bit of baking soda to react with the acidity of the sourdough and create a rise, and mix just to combine. The batter will cook into fluffy, delicious pancakes.
If you prefer to bake right away, simply skip the fermentation step. There will be no predigestion benefit, but you will get a bit of extra rise and flavor from the yeast in the sourdough starter. Simply proceed with the recipe as written.