If you don't, it will seperate again. Here's a blurb I found on the Kraft web site.
http://www.kraftcanada.com/controlle...12159&ctx=5000
Kraft All Natural
How does Canada's favourite peanut butter brand create the rich roasted taste in new All Natural Peanut Butter? We select only quality peanuts and roast them to perfection before blending and sealing fresh in the jar. Best of all, its low in saturated fat, free of cholesterol, lactose and gluten.
With All Natural Peanut Butters the oil separation naturally occurs. For best texture, stir thoroughly when you get the product home from the store then keep refrigerated to avoid separation. You can keep it at room temperature (no safety issues), however you'll have to stir it each time to blend the oils. Enjoy!