What jus gras means
Jus gras is a classic French culinary term meaning fatty juice. It describes the juices from roasted or braised meat served with some or all of their fat left in, rather than skimmed off as in a standard jus. The fat carries a great deal of flavour, so a jus gras tastes richer and rounder and has a silkier texture.
It is made in much the same way as a jus. The roasting tin is deglazed with a little stock, wine or water, scraping up the caramelised juices, then simmered and seasoned, but the fat is not poured away completely, and sometimes the jus is whisked to blend it briefly before serving. In classic French cookery, the term also appears in the phrase au jus gras, describing rice, vegetables or other dishes cooked in meat juices or rich stock with their fat, as opposed to au maigre, meaning cooked without meat or fat.
The term is mostly found in older French cookbooks, professional cookery and restaurant kitchens rather than everyday recipes, though the idea is familiar to anyone who spoons roasting juices and fat over meat at the table. Balance matters, because too much fat makes the sauce greasy. You will see jus gras in classic French recipes and restaurant menus.