In a medium saucepan, combine the soda, vinegar, sugar, paprika, turmeric, star anise, cardamom and orange peel. Bring to a boil over high heat, then reduce the heat to medium and cook until the sauce is thick and syrupy but still pourable, about 30 minutes, depending on the strength of your burner and the size and shape of your saucepan. Set the sauce aside. (The sauce can be cooled and stored in an airtight container in the refrigerator for up to a week.)