I wanted to expand my answer to this question by adding info about the color blue.

Both mother and sour doughs are very stable, but can be 'invaded' by a bacteria that'll give it a bluish taint. I'd throw that dough in the bin (actually, I did once), but I can't find any information confirming that.

So, there's the question: how do you recognize the mother is spoiled?

  • Is the blueish tint in the sourdough itself, or just on top of it? It makes a big difference. – FuzzyChef Sep 11 '11 at 22:12
  • @FuzzyChef, I'm not sure, it was some time ago. I guess it was more on the top. – BaffledCook Sep 12 '11 at 18:54
  • @FuzzyChef, it's just the top. – BaffledCook Feb 12 '12 at 22:06
  • See answer below. – FuzzyChef Feb 19 '12 at 5:19

The sour dough (including the 'mother') should be considered spoiled when:

  • It smells very bad (like voimit or feces). The natural sour dough smell may be not very pleasant to some, but spoiled dough smells really afwul
  • It grows hair. That means mold. And even if it is visible only on the surface, whole dough is spoiled.
  • It gets strange colour. Generally the dough should be white/gray/brownish, maybe with some darker spots when whole grain flour is used. When it becomes black, red or blue – it is bad.
  • It doesn't work. Good sour dough will raise when fed and put it warm place. When it is spoiled it usually won't work any more. Good bacteria and yeast are usually mostly dead when bad bacteria or mold took over the dough.

Based on your comments, your sourdough is probably OK.

It is not uncommon for an older sourdough to get a blue-grey, sludgy mold in the water on top of the sourdough, especially if you're not splitting the dough often enough. This is not fatal. The steps to remedy it are:

  1. Pour off all the water on top of the sourdough.
  2. Scrape off the mold around the sides of the jar and the very top layer of the sourdough.
  3. Spoon out the sourdough, trying to let at little of it swipe against the sides of the jar as possible.
  4. Split the sourdough as normal. Yes, you can use the other half to make stuff, it's completely safe.
  5. Put the culture you're saving back in a new, clean jar.
  6. Clean the old jar and run it through the dishwasher.

I've recovered my sourdough from blue mold several times this way. Actually, I make it a practice to swap jars every time I split it; that helps a lot.

Jacek is correct that if the sourdough smells fecal, or if it's fuzzy, then it's not salvagable. Red or yellow molds are also bad news.

  • OK, I'll swap next time. – BaffledCook Feb 19 '12 at 10:15

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