Hi Maureen, I'm guessing the sponge will require some added yeast, flour and salt to be useable, although make sure the mixture still smells good and isn't showing any signs of mold or bacterial growth before adding ingredients. Feeding the starter you have remaining in the refrigerator sounds like the best idea. Try feeding the 1/2 cup (4 ounces) of starter with 1/2 cup (4 ounces) of water and 1 scant cup (4 ounces) flour at room temperature twice daily (about 12 hours apart). Be sure to discard all but 1/2 cup starter each time you feed it. Within a few days I expect your starter will have a nice, mildly tangy aroma and will be doubling in size after 6-8 hours. Once your starter is showing this kind of predictable behavior, then you can start baking! Barb

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