Who knew, right? I’ve tried this technique multiple times now on some pretty nasty oil that’s cooked frozen french fries, fried oysters, fried okra, fried green tomatoes, and beignets and can attest that it does indeed work. The process is relatively simple:
1/2 cup water + 1 tsp gelatin per quart of used oil.
Wait until the oil has cooled to room temperature. In a separate pot, heat 1/2 cup of water per quart of oil to a simmer and then dissolve 1 tsp gelatin per 1/2 cup. Stir to make sure that gelatin has completely dissolved.
Pour the gelatin mixture into the oil and stir constantly and vigorously until thoroughly incorporated. Cover the pot and put in the refrigerator overnight. In the morning, pour the oil from the pot into a container and then discard the remaining gelatin disk with all the burnt pieces embedded.
In my experience, the clarified oil will be cloudy at first, but after a few days it will clear up.