Yes, after you make the dressing, it should be kept in the refrigerator. The dressing will solidify in the fridge, but this is a good sign. It shows you used quality olive oil for the dressing. Let the dressing sit at room temperature for about 15-20 minutes before serving and then shake it vigorously to blend the ingredients. Alternatively, if you're using balsamic vinegar for salads and like them chilled, they can be refrigerated. If you're using them for sauces, marinades, and reductions, store them in a cool, dry place, like a cabinet.