That’s totally up to you. We have some Moms send their most recent stash to preserve the most nutrients as possible. The sooner breast milk is frozen and then freeze dried, the greater amount of nutrition is preserved. While other Moms send us their oldest milk to provide the extended longevity, prevent further degradation and to make room for more of their stash. If you follow the CDC’s guidelines on expressed breastmilk storage, breast milk is acceptable for 12 months when stored in a freezer.