Fire cider â€" a spicy, zesty, immune-boosting tonic of apple cider vinegar and powerhouse herbs like horseradish, onion, garlic, ginger, and cayenne â€" is an old-time remedy that’s gaining a new generation of fans. Best-selling author and herbalist Rosemary Gladstar has created a compendium of recipes for making and using these cider vinegar tonics.