I used to make soft cheese by vinegar, which quickly results in the formation of curd. I tried to make hard cheese (mozzarella) by
rennet (commercial tablet) by the process took more than 30min and the result was something like yogurt.
I simply followed the manual (mixing the tablet solved in warm water with the milk at temperature 35 - 40 C). Was something wrong with my procedure, milk, or rennet?