I want to know what the difference is between mozzarella that stays white on pizza and the kind that turns yellowish or off white, and also seems more oily. I've found that packaged brands of fresh mozzarella balls (bel gioiosa) or the kind you can buy in water at the grocery store both turn yellowish, whereas this kind that I can get from a local restaurant (they make the mozzarella in house) stays white more like what you see on traditional queen margherita pizzas (see the difference in photos below).
I know this has nothing to do with whether the mozzarella is put on after the pizza is cooked. I kind I buy from the restaurant stays white in the oven, and they definitely put in on before they put the pizza in their ovens. The mozzarella still browns at the edges and bubbles of course, but retains a starker whiteness and a different texture. I'm asking because I want to figure out how to make my own this way, and I want to know what the difference is in the process. I'm thinking it may have to do with milk fat content but I wanted to know if anyone knows for certain. No speculative answers please.