Hi Richard, a starter is a little more prone to developing mold during the creation process because it hasn't yet developed the natural defenses that a fully mature starter has. One thing that can help during the creation process is to be sure to stir your starter thoroughly once a day. Since mold grows from the top down and requires oxygen, stirring will deprive it of oxygen and disrupt any growth. Once you've achieved ed a fully developed starter that is predictably rising and doubling in volume about 6-8 hours after you feed it, it should be fairly mold resistant. That being said, for our starter process you need to feed the starter twice a day when you have it out at room temperature. Extended time at room temperature without feeding or stirring will make it more likely for your starter to develop mold.

If your starter is getting moldy in the refrigerator, this could be a result of mold exposure in the refrigerator, so being sure to cover it well is a good idea. In fact, even when you have your starter out at room temperature, it's fine to cover the container well with plastic wrap or a lid. The reason we say to "cover loosely" isn't 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 top to pop off. As long as you leave sufficient room above the starter level for the gases to accumulate and open the lid now and then to vent the gases, this shouldn't cause any issues. Any food safe container should work well (plastic or glass), but I would put the lid on securely, especially in the refrigerator. 

If you're covering your starter well in the refrigerator, another possible cause of mold development could be your feeding routine. If you tend to feed your starter at room temperature and then stick it right in the refrigerator it may not be getting enough time to ferment and develop the proper amount of acidity. If this happens repeatedly, you end up maintaining what is essentially a flour/water paste, which won't fight off mold as well. For this reason it's important to allow your starter a few hours of fermentation time after feeding and before you stick it in the fridge. 

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