There are a few key differences between kefir grains and a kefir starter. For one, kefir grains are a live culture, meaning that they will continue to grow and reproduce, whereas a starter is a one-time use product. Additionally, kefir grains can be used to make both milk and water kefirs, while starters are generally only intended for milk kefirs. Finally, because they're a live culture, kefir grains will change slightly in taste and texture over time, whereas starters will remain consistent.