Hi Cynthia, we recommend storing your sourdough discard in a separate container in the refrigerator and trying to use it within a week. As long as the container has sufficient "head room" above the starter for fermentation gases to accumulate, it shouldn't cause any problems to put the lid on tight. You can also open the lid now and then to vent the gases. The reason we say that the starter should be "covered loosely" is that fermentation gases can build up in a tightly lidded container and cause the lid to pop off. Barb

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