I got some animal rennet. I used a quarter tsp per gallon of milk as indicated and the first time it worked wonderfully. The second time I used it (maybe two months later) the same amount barely coagulated. I stored it in the refrigerator, but when I picked it up it was wet, making me think it wasn't sealed properly. Should I just add more next time or has my rennet gone bad, or is it just hit-or-miss? Is there a way to test rennet on a test batch?
Note: It is the same recipe. I am making feta with half ultra-pasteurized goat milk and half pasteurized, non homogenized cow milk.