Blue/green mold on sourdough starter

A well-developed sourdough should be able to generate a micro climate within his jar that supresses other growth like mold. This holds especially true for "old", well-established strains. We (1) use a sourdough strain that's been cultivated for at least 20 years. (After that, history becomes a bit murky...)

Young sourdough is the most susceptible to contamination and needs some time to develop a good souring/ leavening ratio. During the first weeks or even months, the baking properties of a sourdough might change quite a bit. So while a sourdough ist "working" after a few days, older lines are preferrable - the various yeasts will adapt to your conditions and develop a stable "society" (for lack of a better word).

As far as your mold problem is concerned, I'd just start over. You will have lost just a few days and your next batch will probably be fine. It's possible that in your moldy batch some "weaker" strains of yeasts grew that couldn't handle other micro-organisms. This happens sometimes. For old strains, I'd be tempted to try a "rescue mission" as described in the other post, but as the outcome is unclear, I wouldn't bother with a new batch. Just follow the instructions carefully, work with clean utensils and perhaps check your water -if it's heavily chlorinated you might be better off with bottled, at least in the beginning.

(1) "We" are a group of bakers that regularly bake and sell artisanal bread for charity.

My sourdough starter has grown mold on top or on the sides of the jar. What should I do?

While mold is fairly uncommon when working with a sourdough starter, it does occasionally happen and is generally caused by either contamination (soap or food residue are the most common) or weakened yeast (skipped feedings, improper ratios, etc.).

Once your sourdough (or the jar) has developed mold, you have a couple of options. You can either try to save the starter or discard the starter and start over. If you decide to save the starter, please use caution and good judgment as mold may just be infecting the surface of the starter or it may have penetrated the starter.

To try and save the starter, remove the molded portion. With a different (clean) utensil, remove a portion of the sourdough that wasn't near the molded portion. You only need about a tablespoon of starter. Put the small amount of clean starter in a new container (be sure there's no soap or food residue), add equal parts flour and water by weight, or one part starter, one part water, and a little less than two parts flour if using measuring cups, mix, cover with a towel or loose lid and allow to proof. Once proofed (bubbly, rising) or within 12 hours, feed the starter again using the same ratios. Continue feeding the starter over several days watching carefully for any signs of mold. If no mold appears and if the starter looks, smells, and tastes okay, proceed to using it for baking or place it in the refrigerator.

Source: http://www.culturesforhealth.com/sourdough-troubleshooting-faq

A lot of great information on that page regarding sourdough if you have time to read through it.

It really takes very little time and cost to begin over, and I have seen so many suggestions that if your starter turns any color other than black, to toss it and begin again. Meaning blue, red, pink...

According to the school of baking: http://www.schoolofbaking.com/sourdough.html

Never allow any form of metal such as a spoon or lid to come into direct contact with the stored, un-used sourdough starter as it will cause a chemical reaction that will contaminate and blacken the implement and eventually in time will kill (loose all activity) the starter and a blackish blue or pink liquid will surface, and the starter at this point, can’t be revived.

I did use a metal spoon once, when in a big hurry, and not sure if it was the problem or a part of the problem, but my 'young' starter nearly died- (quit) - right after that.