Tried to make mozzarella used thermophilic culture and citric acid. Let the bacteria and citric acid sit for 30 min, added rennet, got good curds and whey. When it drained and added curds to hot whey (170) they fell apart and were grainy? What did I do wrong?
You probably got too much acid and too low a pH. Most of the recipes I've seen call for EITHER citric acid, OR thermo cultures. Thermo cultures will create acid over time as the critters eat the lactose and produce lactic acid as a by-product. Pasta fillata requires a fairly specific pH range in order to be stretchable, and if you over-shoot or undershoot, you will get bad curd.