When I first tried cheesemaking (a few years ago now, so I'm a bit hazy on the details), I used junket tablets and Fankhauser's recipes. I was able to get a good set on some recipes, but I threw out at least 5 gallons of putrefying milk from different attempts at his mozzarella/pasta filata. And with no more information to go on, I was left just stumbling about. Very discouraging.
I still don't really know what went wrong, but in retrospect, I imagine the chief cause was insufficient acidification (I was using storebought buttermilk straight from the fridge as my starter, and his moz recipes call for adding the rennet either with the culture or very shortly thereafter). I was never able to get a clean break with his Pasta Filata recipe.
The fact that you did manage to get a clean break, and good curds, means you can't be too far off. I'd say you're probably dealing with too little acid/too weak starter as well (though that's a complete guess and I imagine only one of many things, most of which I have no clue about, which could be causing problems). I'd try the recipe on this site (i.e. CheeseForum.org), or here
, or a variation on this one
Getting mozzarella to spin correctly seems inordinately difficult to me. My last cheese log entry for it said 'I'm done with this until I have a way to measure pH'. (That entry was written at 4am after I'd spent hours waiting for it to hit the point where it'd stretch, and then by the time I got it into the water, I'd overshot it and had cottage cheese. I was pretty discouraged.....at least I still ended up with a tasty cheese, though.)
If you can find some citric acid, you could try the 30 minute mozzarella recipe
, just to help get more feel for how the curds should stretch. The complexity of flavor is definitely not there, but seeing the rennet set up in minutes (actually, mere seconds in my case) is magical. The curds are firm and expel whey with gusto, and when you microwave, everything goes from rough to smooth and elastic with just a few pulls. Also, if it fails, you've spent 30 minutes instead of 8 hours.
Of course, take any of my recommendations with a grain of salt, since aside from the 30 minute stuff, I've only produced real, successfully stretched moz one time -- and even then it didn't stretch that well (and it sat in my refrigerator and on my counter for 3 days (!!) before it hit the point where it would spin).