1. Combine all ingredients in a 12-quart stockpot. Bring to a boil over medium-high heat. Reduce heat to low; simmer 4 hours, skimming and discarding foam as needed. Strain through a cheesecloth-lined colander into a large bowl; discard solids. Cool stock to room temperature. Cover and refrigerate 6 hours or overnight. Skim fat from surface; discard fat.