As you embark on your sourdough journey, understanding the phases of your sourdough starter is crucial. On Day 15, you may observe increased bubbles, indicating active fermentation. Typically, a mature starter should double in size within 4 to 6 hours after feeding—and this is a sign that she is ready to be used for baking. If you're seeing this growth, consider increasing feeding frequency to promote a more robust culture. It’s also essential to monitor the temperature during fermentation as it directly affects the starter's activity. The warmer your environment, the more active your yeast will be. A consistent feeding schedule will help maintain this activity. For beginners, don’t hesitate to explore forums and discussions online about handling sourdough starters. Engaging with a community can provide you with insights and tips from seasoned bakers. Remember, each starter behaves a bit differently, so use these observations as guidelines rather than hard rules. Learning to bake with sourdough involves patience and practice, but the rewards—fresh, homemade bread—are well worth the effort!