The mix is definitely a no-no. Here's some info from Wilkepedia - I'm a Google fanatic!
Quote:
Au Jus means the natural juices given off by the food. [1] To prepare a natural jus, the cook may simply skim off the fat from the juices left after cooking and bring the remaining meat stock and water to a boil. Jus can be frozen for up to two weeks.
Often prepared in the United States is a seasoned sauce with several additional flavourings. American au jus recipes often use soy sauce, Worcestershire sauce, salt, pepper, white or brown sugar, garlic, onion, or other ingredients to make something more like a gravy. So-called jus is sometimes prepared separately, rather than being produced naturally by the food being cooked. An example could be a beef jus made by reducing beef stock to a concentrated form, to accompany a meat dish.
Jus can also be made by extracting the juice from the original meat and combining it with another liquid eg: red wine (thus forming a red wine jus).
A powdered product described as jus is also sold, and is rubbed into the meat before cooking or added afterwards. Powdered forms generally use a combination of salt, dried onion, and sometimes sugar as primary flavoring agents.
