To make your own ground ginger, set a dehydrator to 140°F (60°C). If your fresh ginger has a thin skin, there is no need to peel it, but if the skin is thick, then peel it first. Finely chop the ginger, or grate on the large holes of a box grater. Spread the grated ginger on a dehydrator tray lined with parchment paper or a silicone baking mat. Dehydrate for 24 hours, until the ginger is completely dry. Alternatively, place the grated ginger on a baking sheet and dehydrate in the oven on the lowest setting possible for 1 to 2 hours, until completely dry. Blend the dehydrated ginger on high speed in a spice grinder or liquidizer to a fine powder. Store the ground ginger in an airtight container in the freezer for up to 3 months to keep it fresh. Use in any recipes where ground ginger is called for.