Since fresh raspberries don't last for long, you might like to dry them in a food dehydrator and then you can add the sweet fruit to cakes and cookies, granola, and more. This is one of the best methods to extend their life span by weeks. Wash some firm, ripe ones (not over-ripe because they will fall apart) and then blot them on paper towels. Cut each berry in half, spray with some lemon juice, and then dry in a dehydrator, in the oven, or outside in the sun.