Nuts are fruits that have a hard outer shell that encloses a kernel, which is also called a nut. Seeds are contained in fruits of plants and are capable of reproducing a new plant. An important source of nutrition for thousands of years the world over, nuts and seeds are still staple foods and an important protein source in many cultures. Many nuts and seeds are available both in and out of the shell, whole, halved, sliced, chopped, raw, or roasted. They are popular in both sweet and savory dishes and are often enjoyed as a snack food. Some nuts and seeds are processed to make butters or oils. Because of their high oil content, nuts and seeds are prone to rancidity once shelled and should be stored in an airtight container in the refrigerator where they will keep for several months. Shelled nuts are available in vacuum-sealed cans, glass jars, and sealed bags.