Low-moisture whole-milk mozzarella, bought as a block and grated at home, gives you the best melt on a pizza. It browns without burning, stretches when you pull a slice, and does not flood the pie with water. Fresh mozzarella is the better cheese to eat with a tomato and a spoon of oil, and it is the harder one to put on a pizza successfully.
The difference between them is measurable, and it comes down to a moisture range.
The moisture brackets
There are four mozzarellas in common production, and they differ on two axes: how much water the cheese holds and how much fat sits in the solids.
Fresh mozzarella, the soft kind sold in brine or whey, has a moisture content between about 52 and 60 percent by weight, with a minimum milkfat content of 45 percent of the solids. When made from cow's milk it is sometimes called fior di latte. When made from water buffalo milk it is mozzarella di bufala, softer and wetter still.
Low-moisture mozzarella keeps the same 45 percent minimum milkfat in its solids and drops the water to between about 45 and 52 percent. That is the block in the dairy aisle, sometimes sold simply as "pizza cheese", and it is the cheese on almost every pizza you have eaten in a restaurant.
Part-skim mozzarella matches the fresh standard except that its milkfat, calculated on the solids, falls below 45 percent and stays at or above 30 percent. Low-moisture part-skim applies the same fat reduction to the drier cheese, and it is the one most pizzerias buy by the case.
A seven-point swing in moisture sounds small. On a pizza it is the difference between a browned, blistered surface and a pale one sitting in a puddle.
Low-moisture whole milk as the default
Whole-milk low-moisture mozzarella is the cheese to reach for unless you have a specific reason to choose otherwise. The extra fat browns instead of scorching, it carries flavour that part-skim gives up, and it produces the pull people photograph.
It is also forgiving. It survives a slow home oven at 220 °C (430 °F) and a fast pizza oven above 400 °C (750 °F), it takes toppings on top of it without collapsing, and it does not need draining, salting or blotting before use. Buy it in a block, keep it cold until the moment you grate it, and grate on the large holes so the shreds hold their shape until the cheese melts.
Part-skim behaves differently and not always worse. Less fat means less oil pooling on the surface, which some people prefer on a heavily topped pie, and it gives a chewier, more elastic melt that holds together when a slice is folded. It browns more slowly and it can go rubbery if the bake runs long. On a fold-and-eat slice, that chew is the point.
Many pizzerias blend the two, running mostly part-skim for structure with some whole milk for flavour and colour. That is a reasonable thing to do at home with two blocks and a bowl.
Fresh mozzarella on a home pizza
Fresh mozzarella is glorious and it needs handling. At up to 60 percent water it will release liquid onto your pie, and a home oven bake at 250 °C (480 °F) is too short to drive that water off before the crust is finished.
Three habits fix most of it. Tear the ball into thick irregular pieces instead of slicing it into thin wet discs. Drain the torn pieces on paper towels for at least twenty minutes, and longer if you have the time. Use fewer, larger pieces spread with generous gaps, because the cheese will spread as it melts and you want dry crust between the pools, not one continuous wet layer.
Buffalo mozzarella is wetter still and worth saving for a pie you finish after baking, or for adding in the last minute of a bake. Fior di latte, the cow's milk version, sits closer to manageable.
If you want the look of fresh mozzarella and the behaviour of low-moisture, do what a lot of good pizzerias quietly do: a base layer of grated low-moisture cheese for coverage and melt, with a few torn pieces of fresh mozzarella dropped on top for the soft white pools.
Blocks against bags
Pre-shredded mozzarella is coated with cellulose, potato starch or a similar anti-caking agent to stop the shreds sticking together in the bag. The same coating stops them flowing together in the oven, so the melt looks granular and the surface never goes glossy.
Block cheese costs less, melts better, and takes about ninety seconds to grate. Fresh mozzarella packed in water should be drained and torn. Fresh mozzarella sold in a vacuum pack is drier and more forgiving, and it is the easier one to buy if you do not plan to drain anything.
Keep the grated cheese cold right up to the moment it goes on the dough. Warm mozzarella releases fat before the oven has a chance to set the surface.
Smoked, burrata and the ones that are not mozzarella at all
Smoked mozzarella is low-moisture cheese that has been cold or hot smoked, and it behaves on the pie like the block it started as. Use it in a blend, not alone, because the smoke is loud and it flattens delicate toppings.
Burrata is not a pizza cheese in the baking sense at all. The shell is mozzarella, the inside is cream and curd, and heat splits it. Tear it over a hot pie after the bake and it stays exactly what you bought it for.
Ricotta, provolone and fontina all turn up alongside mozzarella in blends. The three cheese spinach pizza is a good example of what happens when mozzarella does the melting and another cheese does the flavour. Browse the cheese-focused pizzas for more of those combinations.
The block to buy this week
Buy one block of whole-milk low-moisture mozzarella. Grate half of it on the large holes of a box grater, keep the shreds in the fridge until the oven and the stone are as hot as they go, and use less cheese than feels right so the sauce and the crust still register.
Then, on the same pie, tear three or four pieces of drained fresh mozzarella over the top before it goes in. You will taste both cheeses doing separate jobs, and after one bake you will know which of the two you want to buy more of.