Infected sourdough starter?

Greg Lehey

I've been baking pretty much the same style of bread for 18 months now. Early on I split the starters into three separate strains, and I use them alternately. I keep them in the fridge and bake about every 10 days, so each starter is about a month old when I use it. This method has worked well.

A couple of days ago I started a new loaf, but when I looked at the starter, there was some growth on it:

What is that? At first sight it looks like granulated yeast, but the second photo (extreme close-up) makes it look like some kind of worm. The threads are about 0.1 mm apart. I'd be grateful for any ideas.

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Midnite Baker's picture
Midnite Baker 2010 August 26


Hi, Don't know what that is .  I'm a girl and girls usually don't like worms. So..... guess you

know what I'd be doing with it.    Sorry...

peregrine 2010 August 29

Hi Greg,

Unless you can see these things wiggling a bit, they're probably not worms. As bacteria grow in colonies, each species forms a different looking colony, depending on the medium they're growing on. This looks like a particular kind of bacterial colony growing on top of your starter (or it could be a kind of mould). Does it have a strange smell?

Regardless of whether it's a bacterial or mould infestation, it needs to be ditched I'm afraid. Tip it into the compost and soak your container in straight vinegar for 24 hours. Even with this treatment, I wouldn't use that container again for starter.

Wash your hands well before opening up your other starters, as you don't want to inadvertantly spread any spores onto your other starters.

All the best,


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