If you will be using the elderberries right away, you can clean them first, then store them in the fridge for up to a day. If you will use them at a later date, place the cleaned elderberries on a foil-lined tray and freeze them in a single layer. Once frozen, store the berries in ziplock bags. If you dry the berries using a dehydrator, or the oven, you can store them in jars until you are ready to use them.