Yes, mozzarella is presented as an easy cheese ... but reading on this forum has confirmed my own experience, that it is not nearly as easy as it is made out to be. It can be made without cultures--generally using citric acid--and it doesn't need a press, so theoretically it is easier to start with, as you don't have to procure more specialized ingredients and tools. (Though you still need rennet, so ...)
Some folks seem to have the knack of getting the citric-acid version to work right ... but a lot of us have tried it repeatedly and had very mixed results. Maybe it is a function of the milk available; maybe we're just doing something wrong. But the bottom line is that this is not a fool-proof cheese. My own experience is that even when I have gotten it to work, sort of, the "curds" are much more like ricotta than like curds -- the acid causes the milk to separate into a million tiny flecks even before the rennet can do anything. Once, and only once, I was able to drain the result into something like a curd mass, which sort of agreed to stretch ...
Keep in mind that you are aiming for a fairly specific pH range -- 5.2 to 5.4, IIRC. If the pH is too high, the curds won't stretch; if the pH is too low (too much acid), the curds will break up and crumble. So if you have trouble, the problem may not be too little citric acid; it may be too much!
