Pink, Orange, or Fuzzy Mold on Sourdough Starter — Throw It Out
This is the only sourdough problem that means real trouble. Mold has established. The starter cannot be saved by stirring it in or skimming the top off.
Pink, orange, fuzzy, or black spots have appeared on the surface or sides of your jar. You're wondering if you can save it.
What it looks like
- Pink, orange, or salmon-colored spots — usually small at first
- Fuzzy patches of any color (white, gray, green, black)
- Off smell, often sharp or unpleasant in a different way than acetone
- Spots may be on the jar walls, the lid, or floating on top
Why this happens
Dirty jar or utensils
Mold spores enter the jar and find a home — sometimes from a wooden spoon that wasn't rinsed clean, sometimes from a jar that had old crust on the sides feeding spores.
Long stretch with no feedings
A starter ignored for a week or two on the counter loses its acidic protection. The pH rises, and mold can outcompete the yeast that would normally suppress it.
Contaminated flour
Rare but possible. Flour stored damp or past its useful life can introduce mold.
How to fix it
Throw it out
Compost the starter, wash the jar in hot soapy water, and start over. Skimming or stirring will not work — mold mycelium has already penetrated below what you can see.
Sanitize before starting over
Boil the jar, dry completely, use fresh flour from an unopened bag. Switch to a different brand of flour if your current one had been open for a while.
Preventing it next time
- Use clean utensils every time. Anything that touches the starter should be washed since the last feeding.
- Don't go more than a week without a fridge feeding, or a day without a counter feeding.
- Transfer to a clean jar every 1–2 weeks. Crusted-on starter on the jar walls is food for mold.
- A thin gray liquid on top (hooch) is normal — only colored spots or fuzz mean mold.
Most starter problems show up in the data.
Sarah's Sourdough — the iOS app — logs every feeding, photographs every rise, and predicts peak by your kitchen temperature. Problems become visible weeks earlier.
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Related problems
Liquid layer on top (hooch)
Hooch is alcohol. Yeast has metabolized all the available sugars in the flour and produced alcohol as a byproduct. Your starter is hungry, not dying.
Smells like nail polish remover
Your starter is starving. Acetone is what active yeast produces when it's eaten everything in the jar and started consuming itself.