Minecraft wiki entry for Creating_behavior_packs, associated text: In this you see three things, tags, input and output, the input and output define what goes in and what comes out, the tags define in what you can smelt the item, there are 5 tags: "furnace", "blast_furnace", "smoker", "campfire", and "soul_campfire". so in the example of creating a new recipe that only works on campfires, you would only put the tags campfire and soul_campfire.