Place the chicken carcasses, garlic, vegetables, herbs and peppercorns into a large, deep-bottomed pan.
Add the cold water and bring to the boil, skim immediately, then turn heat down to a simmer.
Continue to simmer gently for 2-3 hours, skimming the top every 30 minutes.
Remove from the heat and pass the stock through a fine sieve/strainer.
Allow to cool, then refrigerate.