Blood or Liver

These ingredients add intense richness and color to brown sauces, especially when accompanying game. In Europe, a container of fresh blood may be sold with a game animal, but pig's blood is often substituted. If storing blood for a couple of days, mix it with one or two tablespoons of vinegar to prevent it from coagulating, and refrigerate in an airtight container. Finely chopped raw liver or foie gras can be substituted for blood. Sauce thickened with blood or liver cannot be reheated, otherwise it will curdle.