To Lindy... rendering is exactly what I've been doing to my grease. I was confused at first, because in chemistry, "rendering" means adding a strong acid (e.g., muriatic acid) to the soap solution in order to extract the waxy fatty acids. As for things like ham rind, beef trimmings, etc etc... I typically fry them down, pour and screen out as much grease as I can, then feed the fried pieces of meat to my dog. The ickies are then pretty much absent, but OTOH the grease will be yellow and have a meaty smell until it's steamed.
To Mike... thanks for the tip! Friends from the South who eat a lot of chitterlings have told me vinegar in the pot will make the cooking less stinky, so I'll definitely try it once I save more raw grease. The chemicals in grease after meat has been cooked in it, are mostly nitrogen-based alkalies (one, liquid quinoline, smells like burnt steak)... so an acid like vinegar ought to neutralize them pretty well.
Still dunno how well it would work against rancidity, though I could always try it and post the results...