Article: Your gravy is done when it coats a spoon and comes off in drips – not a steady, thin stream. This could take around 10-15 minutes.  Stir it regularly so it doesn't film over, the bottom doesn't overheat, and the air and heat circulate evenly. It will take a while, so be patient. It's not done yet! Don't be alarmed if it still seems like it's in the works, because it is!

What is a summary?
Keep it over low heat to thicken.