The first time you open a new jar of tahini, it will most likely be separated. Stir it before refrigerating it, as it will be difficult to stir when it is cold. If it separates while sitting in the refrigerator, leave it out until it comes to room temperature and stir it.    Some folks suggest dumping it into a bowl and stirring or using an immersion blender, storing it upside down to get the hard, settled paste to the top, or microwaving it in short bursts before stirring. I’ve never tried these, I use a butter knife or fork to break up the paste and stir, stir, stir.