Hi, Mary. As the yeast and bacteria in your starter grow, they create both lactic and acetic acid. Starter in need of feeding is usually fairly acidic; that's why it's necessary to discard some of it. When you add fresh flour and water to the starter, they need an environment that will encourage growth. While yeast doesn't mind some acid, too much will keep it from embarking on a growth rate that produces enough bubbles to help bread rise. With the sweet recipes in this post, the discard you use is in the formula for moisture, flavor, and tenderness. Susan

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