Olive Oil / Duck Fat Safety
A few months ago I made Ruhlman's Olive Oil Duck Confit. The duck has been eaten, but I left the oil in my dutch oven and kept it in the refrigerator to hopefully use again for another batch. So I've got 2 layers; the bottom layer is darkish brown with a jello-like consistency, and the olive oil is solidified in a harder layer on top. I'm not sure if the bottom layer is straight duck fat, as the duck fat that I usually see is not this dark. Everything smells fine and even tastes fine. Is this safe to use again?
The "dark brown" layer causes me to suspect you may have overcooked what would normally be cracklings; hard to know for sure.
Of course, without being intimately familiar with the history of the reserved oils, there's no way to know for certain how "safe" your reserved duck fat/olive oil might be. But if I were to entertain the notion of using it again I'd definately carefully remove everything above the dark brown layer and toss out the bottom layer.