The historic way to thicken the sauce in coq au vin was to add animal blood, as it was the least expensive method.
Stories say that this dish can be traced back to the times of Julius Caesar, though the recipe wasn’t documented until the early twentieth century. Traditionally, cockerel, which was tougher than ordinary chicken, would have been used in coq au vin. However, later recipes specify that any chicken can be added. The historic way to thicken the sauce in coq au vin was to add animal blood, as it was the least expensive method.