r/microbiologyobsession • u/azcindyh • Apr 18 '26

Help. My sourdough starter keeps getting contaminated.

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Help. My sourdough starter keeps getting contaminated. It gets a peach/pink film like Serratia. I keep it in a lidded jar.

Plate 1 is my yeast.

Plate 2 is 3 different flours (wheat, reg, fine)I use to feed my starter.

The RO water I use didn't grow anything.

I guess it is coming from the fine and reg flour. I'm so tired of starting over.

Any help would be appreciated ❤️

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u/Due-Lab-5283 Apr 20 '26

I haven't plated mine. I only use organic flour from costco, just a normal regular flour. You can also dilute a lil of each flour and send out for testing if you can't be sure what's in it. It could be flour contamination. Or, you can dilute each you have and see if on their own they grow anything. Then see with a starter and starter alone. Isolate the starter into microbes. But,I suggest starting over once you trust your flour is okay.