Infuse and Cool the Marinade
Combine red wine, red wine vinegar, onion, carrots, leek, celery, garlic, bay leaves, juniper berries, cloves, allspice, peppercorns, brown sugar, and salt in a large saucepan over medium-high heat. Bring to a brief boil, reduce heat to low, and simmer for 5 minutes. Remove from heat and allow to cool completely to room temperature.
Simmering blooms essential oils in the whole spices and dissolves elements uniformly. The liquid must be completely cold to prevent flash-cooking the raw beef exterior.
Highly aromatic, deep-purple liquid with slightly softened vegetables.