When I buy fresh ground peanut butter, it has a very dry, paste-like texture with almost no oil. It can sit on my shelf for a week in warm weather and no oil separates out.
When I buy peanut butter in a jar, it has a layer of oil on top. Once this is mixed in, the texture is creamy and oily at room temperature.
The label claims that the jar contains only dry roasted peanuts, nothing more. This seems to be the case for all brands I've seen. Where does all the extra oil come from?
Best Answer
The difference may be in how finely the peanuts are ground. Depending on the stores machine, you may not be getting a perfectly smooth peanut butter which means there is still some residual oil in there.
Also, a week after fresh-ground is still very fresh. That jar of xyz brand on the shelf can be six months or older. If you leave your fresh ground out for longer, it most likely will separate.
The other bit might be that the oil comes out when the grinding processes warms up the peanuts, and your local store's machine might still keep them cool enough. You can see a similar effect with coffee beans and their roasting temperature. Speaking of which, the commercial process might also roast at different temperature.
What I have noticed is that if I let our Vitamix blender go at the peanuts a little longer, the oil does eventually get coaxed out and that batch will have its oil separate eventually.