Marzipan is used extensively in European pastry shops. It will keep almost indefinitely if you take proper care in mixing and handling it. It should be stored in airtight containers in a very cool place or in the refrigerator. It can also be stored in the freezer, should you need to keep it for a long time. If the oil separates from the marzipan after it thaws, add a small amount of water and some powdered sugar. Continue to knead until smooth and elastic.