Rendered Fat

For foie gras: Cut the foie gras (or trimmings) into ¼-inch pieces.

For beef marrow: Cut the fat into ½-inch pieces.

For duck fat and skin: Grind through a grinder fitted with a medium die.

For beef fat and sinew: Grind through a grinder fitted with a medium die.

Vacuum-pack the fat in a bag on medium. Cook at 85°C (185°F). The foie gras fat should be rendered after about 45 minutes, the marrow after about 1 hour, and the duck and beef fat after about 1½ hours.

When fat is rendered on the stovetop, any water evaporates in the cooking process. Here it remains in the bag and so must be separated from the fat. Strain the rendered fat through a chinois or fine-mesh conical strainer into a deep, narrow container and refrigerate. The fat will rise to the top and solidify. Remove the fat and refrigerate, or freeze for longer storage. The remaining liquid, which may jell, can be discarded or used for another purpose, such as fortifying a stock or sauce.