I always heat jars in the oven for a while and pour the hot fat and jelly in. It's pretend canning, but I keep it all in the fridge. The french have preserved duck meat using this method (without refridge) long before they smoked cigarettes.

The idea, I believe, is fat seals O2 from the content below --- until you reach down into the jelly you are OK. BTW, That jelly is delicious. You can (I do) reheat and start over again if you are worried.