It is skimmed frequently during the process to remove any scum or fat, and seasoned to form the base of all brown sauces. At lunch, a thick veal chop from the top of the leg of veal would be broiled, and tossed in the pot. About two or three hours later, that chop would be my lunch. Veal does wonders for a brown stock, and the feeling is mutual. The loin end chop of pork would often suffer just so fine a fate, with equally good results.
Meat is what makes a good brown sauce.
One taste of the brown sauce in a good beef stew will convince you of that beyond any argument. My best brown sauces were made with surplus braised or pot roasted brisket of beef gravy. Then we follow with some basic recipes that naturally follow the brown sauce pattern, stews and braisings. The last two recipes, are somewhat more difficult to prepare, but rely on the ideas that I have used in the past. Syrupy thick when hot, it is rubbery when cold.