Raisins can be a healthy, sweet treat for adults and children alike. To ensure the quality of the raisins your family eats, consider making your own using a food dehydrator. To get big and dark raisins perfect for oatmeal cookies, choose some fresh plump, purple grapes. For a smaller, light-colored raisin, use tender green grapes. The dehydrating process is not complicated, and making your own raisins ensures that you know exactly where your sweet treat comes from and how fresh it is.