Hi Emily, mold is not a good sign because it indicates that your starter does not possess the normal defense mechanisms of a healthy, established starter. You didn't mention how old your starter is, but if mold is appearing every day, I suspect it would be best to start over. However, you could try reviving a very small portion of healthy-looking starter in a clean jar and see if the mold persists. I would recommend feeding your starter twice a day when it is stored at room temperature, which will help prevent mold spores from permeating the starter. Mold starts on the surface, where there is available oxygen, so stirring the starter will disrupt mold growth.

Ideally you want to feed your starter when it's at its peak of rising, or just beginning to fall, so if your starter is collapsing significantly between feedings this is definitely a sign that you need to step up your feeding routine. I would also recommend covering your starter container a little more securely with plastic wrap or even a lid. The reason we say to "cover loosely" is not because the starter needs airflow in order to ferment properly (it doesn't), but because fermentation gases can build up in a tightly lidded container and cause the lid to pop off. Plastic wrap will flex, and as long as there is sufficient head room above the level of the starter in your jar for the gases to collect, and you open  the jar now and then, a lid will also work fine. 

Mold is everywhere, so it's not as much a matter of cleanliness as it is building the health and resistance of your starter through regular and consistent feeding. Here's the sourdough starter maintenance routine we generally recommend. Sometimes, especially if you live in a very warm climate that is over 80 degrees much of the time, it's necessary to tweak the ratio of ingredients to help slow down fermentation. To that end, offering your starter a relatively larger feeding (less starter as compared to water/flour fed, by weight) will slow things down, and hopefully allow you to replenish (feed) your starter when it's closer to its peak. For example, you may want to try a 1:2:2 or even 1:3:3 ratio of starter:water:flour, by weight. Keep in mind that you can decrease the portion of starter relative to the water and flour, so a "larger feeding" doesn't have to mean using up more flour.

I hope this helps! Let us know how it goes. 

Barb

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