Hi Lella, the reason we say to "cover loosely" is because fermentation gases can build up in a tightly lidded container and cause the lid to pop off. The starter doesn't actually need exposure to air in order to ferment. I haven't noticed any issues with keeping the lid on these little pots as long as there's some head room for the gases and I open the jars every now and then. The crock we sell doesn't have a tight seal, so you don't need to worry about the gases building up. Keeping the starter moist and preventing the surface from drying out is another concern, so we don't recommend covering with cheesecloth or a dish towel. Barb

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