1. Add the chicken carcass, onion, celery, carrots, garlic, apple cider vinegar, herbs, and peppercorns to the bottom of a large stock pot.
2. Pour 12 cups of cold water into the stock pot. Cover and turn the heat to medium. You want to bring the liquid to a low simmer. You don't want to boil the liquid.
3. Let the stock simmer on medium-low heat for 3-4 hours on medium-low heat.
4. After 3-4 hours, you will want to strain the stock. Set a fine-mesh strainer lined with cheesecloth on top of a large bowl. Ladle the stock into the strainer, pressing on the contents in the strainer to extract all of the stock. When you finish this step, you should have about 6-8 cups of chicken stock. This amount varies significantly due to the amount of evaporation during simmering.
5. To store the chicken stock, ladle it into glass jars and let it cool completely on the countertop. Once cool, you can store it in the refrigerator for up to a week. Or you can freeze the stock for up to 6 months!