Hi Rachel, I'm sorry I wasn't able to reply to your question more promptly! It sounds like what you may have seen was mold, which is usually an indication that it's time to start over. Sourdough starters during the creation process are particularly prone to mold because they haven't yet developed the natural defense mechanisms of a mature starter. And mold is naturally everywhere—in the air, and in the flour. Mixing water and flour and letting it sit out untouched for a few days is practially an invitation for mold. However, there are some things you can do to try to prevent mold from taking over your starter. The best defense is to avoid leaving it longer than 24 hours without feeding it (or at least stirring it), especially when it's very new. Mold needs oxygen, which is why it develops on the surface of the starter; stirring the starter will disrupt this growth by robbing it of oxygen. All that being said, if you continued to feed your starter and haven't seen any more greenish streaks, then I would proceed with confidence. In this case, you were likely able to flush it out and your starter is continuing to develop its natural defenses. Good luck and let us know how it goes! 

Barb

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