I've been working on that mozz howto for a while and have been tweaking it. I think the issue of acidity has been oversimplified. In previous versions, I've tried using only buttermilk or yogurt, to have a way to make mozz using common ingredients. But it turns out best using either specific yogurt and buttermilks mixed together, or using DVI culture. It's really tough to get it right using either meso or thermo culture because all mozz I know of uses this intermediate bacteria, Streptococcus thermophilus. It's key to a proper tenderness because it works across a wide range of temps, and is very active at the lower range of normal thermophilic L helveticus or bulgaricus.
By acidity oversimplified, I mean there's more to mozz than a straight acidity drop. I've made mozz before using a single variant culture, and let the acidity drop, and it still turned out dry. Curd size was right, fat content was right, temps were right, etc. So something about the culture selection is making the difference. I think that to get the tenderness, those caseins need to be able to retain water. More acidity helps with that, but I think the cultures break down caseins in different ways and at different rates. Cultures produce more than just lactic acid. They also produce byproducts. The combination of byproducts from S thermophilus is like easy fuel for the L helveticus or bulgaricus, and then it grows rapidly and acidifies rapidly even at the low end of thermophilic temps.
End summary point of all that: you need the right ratio of coccus to bacillus bacteria shapes, and the coccus must include S thermophilus.
I also am thinking of completely abandoning the long culture method because I've had excessive moisture loss when letting the acidity build for more than 6 hours. Solution instead is to preacidify and rennet at 6.2-6.3. That way you get the right texture in 3-4 hours.
That howto is still a work in progress, but I'm getting close. Mozz is tricky, hopefully I can finalize the exact steps to make exactly consistent, soft mozz without needing pH meters.