Bring 4 liters of water to a boil over high heat. Add 1 carrot, 1 onion, 1 leek, 5 parsley stalks, 1 bay leaf, 2 juniper berries, 1 teaspoon peppercorns, 1 teaspoon salt, and 100 ml white wine vinegar.
Carefully wash the 4 trout and remove any innards, being very gentle to avoid damaging the mucus layer.
Gently slide the trout into the stock. Poach over low heat for 10 minutes.