I've been trying to start a sourdough culture for the past week and keep seeing this pink/orange layer on top that I'm pretty sure is mold. I'm leaving it on my kitchen counter at room temperature, feeding it daily with all-purpose flour and filtered water. Should I be doing something differently to avoid contamination?
What ratio are you using when you feed it - like how much starter to flour to water? That pink/orange layer is likely mold, yeah, and it usually means either your jar isn't clean enough or there's too much moisture sitting there. Make sure you're using a very clean (ideally sterilized) jar, keep the ratio balanced so it's not too wet, and if you see that discoloration again, just scoop it off along with the top layer underneath and start fresh with a clean feeding. Most folks find it helps to feed twice a day instead of once, which keeps things moving and less hospitable to mold - does that fit your schedule?
That pink or orange layer is almost certainly mold, and the main thing that stops it is keeping your jar covered properly and making sure your ratio of starter to fresh flour and water is right. You want to use a jar with a loose lid or cloth cover - something that lets gas escape but keeps dust and airborne spores out. The biggest mistake people make is using a sealed lid, which traps too much moisture and creates the perfect environment for mold. A coffee filter secured with a rubber band works great, or just drape cheesecloth over the opening.
Your feeding routine matters too. A common issue is not feeding frequently enough or using too much old starter relative to new flour. I'd suggest using a 1:1:1 ratio by weight - one part starter, one part flour, one part water - and feeding twice daily if your kitchen is warm. If you're only feeding once a day, the culture gets too acidic and weak, and that's when mold moves in. Also, switch to unbleached bread flour or whole wheat flour mixed in; all-purpose can work but whole grain tends to ferment more vigorously and outcompetes contamination. The filtered water is good, but make sure your spoon and jar are clean.
If that growth is already there, you should probably start over. Just dump what you have and begin fresh with a clean jar. The good news is that once you get a healthy starter going with proper ventilation and regular feeding, mold becomes pretty rare. You'll know it's healthy when you see bubbles throughout and it smells pleasantly sour - not musty or off.
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