I purchasesd a Presto dehydrator to dehydrate sweet potatoes for Grace as it is kind of pricey to buy ones made in the USA. Anyway, I slice them about 1/4 inch thick, put them in raw and dry for about 5 to 7 hours depending on the size of the slice. When they are done they are dry but not crunchy (Grace likes them chewy) but when I store them in an airtight container I end up with some have sticky wet spots on them? I make sure they are totally dried and cooled before I store them. What am I doing wrong?