With nothing added to keep it emulsified, the oil in natural peanut butter tends to separate and float to the top of the jar. This is the state in which you usually find natural peanut butter at the market. Stirring the oil back in takes elbow grease, but you can get gravity to do the work for you. When you get the jar home, just turn it upside down and leave it on the counter overnight. Once gravity mixes the oil back in, store the peanut butter in the refrigerator, both to keep it fresh and to solidify the oil so it can’t separate as easily.