Chances are you’ve had a pizza that was covered with mozzarella. It is one of the most common cheeses for a pizza. It melts very well on top of your pizza and turns a nice brown.
The mozzarella used on top of a pizza is often (but certainly not always) the low moist version of mozzarella. This one is sturdy and dried and works great for a pizza. There’s another world of mozzarella out there though: that of fresh, moist mozzarella. This one doesn’t work as well on pizza (because of the higher water content). But is great to eat fresh, maybe with a slice of tomato and some basil (the classic way). It’s the cheese that originated in Italy and was originally made with buffalo’s milk.
Fresh mozzarella has quite a unique stretchy texture to it, an that’s all because of the way it is made, as we got to see first hand when visiting a store that makes their own mozzarella.
What is fresh Mozzarella?
Most of the mozzarella you can buy in stores nowadays is low moisture. This cheese can be stored for months and is a firm block. However, high moisture mozzarella, the traditional mozzarella, is very different. First of all, it has to be eaten fresh. Even if stored refrigerated it will spoil in a matter of days/few weeks.
The texture is also not very suitable for shredding, it lends itself more to cutting or slicing in smaller pieces. Originally the mozzarella would be made from buffalo’s milk, however, a lot of mozzarella’s nowadays are made from cow’s milk (although this does depend on your region).
The high moisture content, which is over 50%, is partly cause for this short shelf life. It is also though what gives it those unique textures and softness when eaten.
Mozzarella is just one example of a stretched curd cheese, called pasata filate in Italian. As we will discuss further down, mozzarella is produced by stretching the curs. This stretching is what gives the cheese its unique texture. Those two steps: curd making & stretching the cheese are the most important steps for making a fresh mozzarella.
Curdling the milk
Just as any other cheese, making mozzarella starts with curdling the milk. During curdling of the milk the casein proteins start to aggregate and form curds in the remaining whey (we discussed casein in more detail before).
Curdling can be done by either acid (e.g. citric acid in the case of paneer) or rennet. In the case of mozzarella rennet is used in combination with a starter culture. This starter culture consists of bacteria that produce acids which will bring down the pH of the milk. The rennet in the meantime initiates the curdling.
Once the milk has curdled, it will be kept for a while to ensure the correct pH is achieved and for the curd to stabilize. It is then cut into pieces/blocks, ready for being transformed into mozzarella.
These blocks are still quite tasteless and bland and have a texture that is quite similar to that of paneer. It is the next step that gives it its smooth texture and appealing taste.
Manufacturers will have to adjust their production processes to where and when the curds will be transformed into mozzarella. If they are done so immediately thyey want to have the right acidity, etc. in one go. However, as is the case for the shop we went to, the curds won’t be immediately processed into mozzarella. Therefore, they have to adjust their cultures and processes slightly to ensure the curds are good to go at the right point in time!
Transforming curd into Mozzarella
Most stores that make their own fresh mozzarella will not make the it from scratch, that is start with the milk. Instead, they will start with the curd that has already been made. It’s here that the mozzarella fun really starts and where our mozzarella demonstration began.
Step 1: Cutting the curds
First of all, those mozzarella curds have to be cut. The size to which you cut them will impact the final texture. The smaller the pieces, the drier the mozzarella since it’s easier for the moisture to escape.
Step 2: Heating up & flavouring the curds
As we mentioned, those unflavoured fresh curds are still quite bland. That is why the next step start by adding a good amount of salty water. This serves two purposes. One is to flavour the cheese and add some saltiness (adding salt is also good to extend shelf life). The hot water at the same time is necessary to warm up the cheese, soften the fats and other ingredients.
The mozzarella maker (whether it’s a person or a machine) will stir the mixture until the curds pieces start blending together into one solid mass.
Step 3: Stretching the mozzarella
Next up: stretching the mozzarella. The mozzarella has started to form one large mass, however, is isn’t very stringy yet. The maker will now stretch the cheese curds. During this process all the proteins will align nicely and the fat will sit in between the protein strands.
Step 4: Making mozzarella balls
Even though this step looks easy, it needs quite a bit of practice to get it right. Pieces are pulled off the large humped of aligned mozzarella cheese and shaped into nice balls. The mozzarella maker now has to make sure that the outside of the mozzarella has a nice layered protein texture and holds together well. Right after the ball is shaped it is dropped into cold water. The cold water will set the fat and protein and helps it maintain its shape.
Most fresh mozzarella is then either vacuum packaged or stored inside whey liquid to prevent it from drying out.
Eating & storing mozzarella
As we mentioned in the introduction, fresh mozzarella has a very short shelf life. It can only be stored for a couple of days (in the fridge that is) after it has been made. Of course, the salt water helps to improve shelf life (by reducing growth of micro organisms), but it is still quite perishable.
Packaging will help to improve the shelf life. One option is to vacuum pack the cheese. The absence of air (and thus oxygen) in these packages prevents oxidation of the fat in the cheese. Oxidation can lead to rancidity and off flavours. Also, it prevents any dry regions from forming. Drier areas in a pack might be a good place for yeast and moulds to grow.
Another commonly used option is to pack the mozzarella balls in cups filled with whey. The whey will ensure the cheese stays moist and doesn’t lose its water. Also, it protects the ball against some growth of micro organisms by keeping it very wet.
That said, mozzarella cheese is still very prone to spoilage by microorganisms. Therefore, it is best to just eat the cheese quick enough and enjoy its unique stretchy behaviour and rich flavour.
New England cheesemaking supply co., Mozzarella cheese making recipe, link ; Great resource if you’d like to give making your own mozzarella a try!
Oldways,Mozzarella di Bufala and Stracciatella di Bufala, link
Michael Tunick, The science of cheese, 2014, p.48, link
Patrick Fox, et al., The fundamentals of cheese science, 2016, p.50-52, link
Yiu Hui, Handbook of food science, technology and engineering, 2006, ch. 150, link
P. Fox, Cheese: chemistry, physics and microbiology, 2012, ch.12 (mozzarella & pizza cheese), link