How can I remove the oil from the top of a jar of peanut butter? Also, can I use the oil for cooking?
Like you, I suspect, I prefer so-called "natural" peanut butter with no added ingredients over those made with hydrogenated oils and sugar. I find the other stuff gives it an unpleaseant texture and a cloyingly sweet taste. Ground up peanuts without anything extra has a clean taste of the nuts. Admittedly I do add a sprinkle of salt on my nearly-nightly slice of bread and peanut butter to bring out the taste, but that's it.
The problem, however, is what to do with the oil that rises to the top. You can stir the oil in, but that makes the peanut butter runny at room temperatures, resulting in PB&Js that ooze down your shirt front, so I always remove it. After many tries of many methods (pouring, skimming, blotting, ...), I have come up with a nearly perfect solution.
First, I store the peanut butter away for a while once it gets home to allow any mixing that has happened during travel to settle back out. Then I remove the safety seal under the lid, put the lid back on and put the jar in my freezer. After a couple of hours the peanut butter has frozen somewhat but the oil has only thickened. If I time it right, I can use a spoon to collect the oil off the top. Because the PB is frozen, the spoon skims over collecting only the oil. Usually by the time I'm done a little of the oil has melted and pooled in the edges, but a quick blot with a piece of paper towel removes it, leaving the peanut butter behind.
While I prefer this, and while it makes the peanut butter a little healthier to eat by removing those fat calories, it does have the downside that sometimes the peanut butter, especially at the bottom of the jar, may become too thick to spread easily. The perfect solution to that is to make peanut butter bush pies. Either that or stir in a little of whatever oil you have on hand to loosen it up a bit.
To your second question, the oil you skim off is edible and pretty much the same as the store-bought peanut oil. The main difference is that commercial peanut oil is filtered to remove suspended solids and impurities. The oil off of a jar of peanut butter contains suspended solids that may burn when heated, giving food and unpleasant taste.