The Starter Invaders: Mold, Kahm, and Pink Streaks
When you open your jar to find fuzzy islands, wrinkled skins, or neon streaks, it is a sign that the pact has been broken. The acid was not strong enough, or the invader was too resilient.
The Sourdough Ash Ratio
When you feed your starter exclusively with white bread flour, you are effectively putting your microbial colony on a diet of pure sugar while denying them the vitamins they need to metabolise it. You are creating a starter that is energy-rich but nutrient-poor.