Say pizza cheese and mozzarella comes to mind, but the mozzarella used on pizza is not the same product as the mozzarella eaten in a salad. The difference is water content, and that difference decides everything else.
What kind of cheese is mozzarella?
Mozzarella is produced by a method called pasta filata — literally "spun paste" — and takes its name from the process itself.
After the milk is cultured, the curd is cut and held until it reaches a specific acidity. That value sits around pH 5.2 and it is critical: higher and the curd will not stretch, lower and it tears.
Curd at the right acidity is transferred into hot water and stretched and folded by hand or machine. This aligns the casein proteins into parallel fibres. The way mozzarella extends when pulled and separates into strands when torn comes from here.
Fresh versus low-moisture: what changes?
Fresh mozzarella — fior di latte, bufala — contains 55 to 60 percent water. It is sold in brine or in its own liquid and eaten within a few days.
Low-moisture mozzarella contains 45 to 52 percent water. It is sold in blocks, keeps for several weeks and shreds well.
Pizza uses the second. The reason is simple: fresh mozzarella releases its water in the oven and a pool forms on top of the dough. The dough absorbs that water and the base stays raw.
It would be wrong to say fresh mozzarella is never used on pizza. Neapolitan pizza uses it — but there the oven runs at 450 degrees and the pizza bakes in ninety seconds, so the water has time to evaporate. A home oven, or a 280-degree conveyor oven, will not give the same result.
What determines melting behaviour?
Three variables: water, fat and calcium.
Water lowers the melting temperature. A moister cheese melts earlier and flows more.
Fat slips between the protein network during melting and eases the flow. Reduced-fat mozzarella does not melt; it softens and turns rubbery. Using it on pizza is a common mistake.
Calcium holds the protein network tight. The lower the acidity during production, the more calcium leaves the curd and the looser the network becomes. This is why two mozzarellas with the same water content can melt differently.
| Type | Water | Behaviour in the oven | Use |
|---|---|---|---|
| Fresh (fior di latte) | 55-60% | Releases water, melts fast | Neapolitan pizza, salad |
| Low-moisture block | 45-52% | Even melt, blisters | Classic pizza |
| Reduced fat | 50-55% | Will not melt, rubbery | Not recommended |
| Pre-shredded pack | 45-50% | Slower melt due to starch | Convenience |
Why is there starch in pre-shredded packs?
Shredded mozzarella packs usually contain potato or corn starch, at around two percent.
Its job is to prevent clumping. Shredded cheese has a large surface area and the strands stick together; the starch coats those surfaces and keeps them apart.
The side effect is a slightly slower melt. Starch first draws water when heated, then gels, so the cheese takes a few extra seconds to flow.
If you shred your own there is no such problem, but shredded cheese clumps in the fridge within a day. Freeze it if you are not using it right away; frozen shredded mozzarella can be scattered straight onto the pizza.
Why do blisters form on pizza?
The brown blisters that appear on the cheese surface in the oven come from steam trapped underneath.
Once the cheese melts and closes the surface, the moisture below turns to steam and pushes the cheese layer upward. The top of the blister has a thin layer of fat, so it dries and browns quickly.
The amount of blistering relates to water content. Very moist cheese blisters excessively; very dry cheese does not blister at all and the surface stays dull.
If you do not want blistering, spread the cheese under the toppings rather than directly on the sauce. Cheese in contact with the sauce blisters less.
What to check when buying
The first thing to read is water content or dry matter. If the label says "fat in dry matter", that is the fat proportion after water is removed; it should not be confused with total fat.
The second is the milk. Cow's milk is standard; buffalo milk is fattier and softer, with limited use on pizza.
The third is the format. Block product lasts longer than shredded and contains no starch. If your daily use is high, buying block is both cheaper and gives a better result.
Finally there is frozen mozzarella. Freezing a block damages the texture somewhat and the cheese crumbles; that is a problem for raw eating but goes unnoticed on a pizza.
How should mozzarella be stored?
Unopened block mozzarella keeps for four to six weeks from production at two to four degrees.
Once the pack is opened, that drops to a few days. The reason is surface moisture: exposed to air, the cheese surface dries, the dried area yellows, and melting fails in that area.
Wrap an opened block tightly in cling film with no air pockets. A fridge bag is not enough, because air stays trapped inside it.
Shredded product should be used within one to two days of opening. If it needs to keep longer, freezing is the only correct route.
Fresh mozzarella is stored in its own liquid, and that liquid should not be poured away. Drain it and the cheese starts drying from the outside and turns rubbery within a day.
Can mozzarella be frozen?
Block mozzarella can be frozen, but it helps to know the outcome.
During freezing the water inside the cheese crystallises and mechanically breaks the protein network. On thawing, the cheese releases some water and the texture crumbles.
On a pizza that difference is invisible; the cheese is going to melt anyway. In a salad or on a cold plate it shows clearly.
The right method is to shred before freezing. Shredded pieces are small, so crystal damage is less pronounced, and the product can go from the freezer straight onto the pizza.
If you do thaw it, thaw slowly in the fridge. Cheese thawed at room temperature wets on the outside while staying frozen inside, and melts unevenly in the oven.
Mozzarella that has been thawed once should not be refrozen; water loss increases noticeably on the second round.
