Place bones in a large stockpot or slow cooker
Add enough cold water to cover the bones
Add 1 to 2 tablespoons of apple cider vinegar
Let the bones soak for 20 to 30 minutes
Bring to a gentle boil, then reduce to a low simmer
Skim off any foam that rises to the surface
Add onions, carrots, celery, garlic, and herbs if desired
Simmer chicken bones for 12 to 24 hours
Simmer beef or pork bones for 24 to 48 hours
Add water as needed to keep bones covered
Strain the broth through a fine mesh strainer
Discard the solids
Cool the broth quickly
Refrigerate and remove the solid fat if desired
Store in the refrigerator for up to 5 days
Freeze for longer storage