Natural peanut butter, which contains only peanuts and sometimes jaggery or salt, without added preservatives or stabilizers, can be more prone to oil separation and spoilage. It's generally a good idea to refrigerate natural peanut butter after opening to extend its shelf life. The cold temperature in the fridge slows down oil separation and helps prevent spoilage. However, it may become thicker and harder to spread when refrigerated, so you might want to let it come to room temperature before using it.