It is normal for the activation batch of a reusable yogurt or buttermilk culture to not set well. It may even remain liquid like milk. While not quite the best for spooning, your milk is still cultured and can be used in several ways.
The most popular use is to add the milk to your favorite smoothie recipe. Need inspiration? We have plenty of ideas! A Complete Guide to Cultured Smoothies.
Regardless of how you choose to use your activation batch left-overs, be sure to save enough to make your next batch of yogurt.