Home-made yogurt ok to eat?

I made whole milk yogurt as usual (i make it in a crock pot which usually works pretty well) and mixed in some yogurt from the last batch and set it to culture overnight. Im not sure it stayed warm enough since its been so cold out, and my house has heat issues. So when I went to check it in the morning it was VERY runny, with small bubbles around the edges and kind of chalky-ish on the tongue. My question: Is it still safe to eat? It smells like yogurt but I'm apprehensive if its not 100% sure its ok. Is there any way to tell?