Melbourne University is set to become one of the cheesiest in Australia.

The secrets of mozzarella cheese are being unravelled at the ARC Dairy Innovation Hub to help mozzarella producers improve their manufacturing process.

Studies will be undertaken by PhD student Anita Pax along with experts from the Bio 21 Institute.

Traditional knowledge of mozzarella-making was first brought to Australia by Italian migrants. Now, mozzarella is produced on an industrial scale, but manufacturers are keen to retain the properties that make mozzarella great.

“Mozzarella cheese is a popular choice for pizza because it melts nicely. You get an even coating and a nice nut-brown colour when it’s heated. When you lift it, you get all the strands,” said Anita.

“I am looking at the properties of cheese and how this is reflected in its molecular structure. I want to understand why it stretches. I am also comparing cheeses for use in pizzas,” she said.

Ms Pax has set up a testing rig that melts mozzarella cheese on a cracker at 240 degrees Celcius for five minutes.

The sample is then transferred to an instrument that measures the force required to stretch cheese by pulling it upward at a constant speed.

Cheese is made of milk, bacteria, rennet (the enzyme that coagulates milk) and salt, but the simple combination can create endless possibilities.

Milk, lactic acid, bacteria and rennet are heated to 38 degrees Celcius, an ideal temperature for the bacteria to divide.

As the bacteria multiply, the whey (liquid) and curd (solid milk proteins) separate out. This is a result of the pH, or acidity, dropping due to the bacterial metabolites.

“The solid milk protein, called ‘curd’ is cut into one cm cubes and allowed to set for 40 minutes, creating a milk ‘gel’. On a microstructural level, this is a jumble of protein and fat,” Ms Pax said.

The liquid whey is drained off leaving the curd at a pH of 5.1 – 5.2, which is ideal for stretching.

Curd is then heated in boiling salty brine and taken out intermittently and stretched. Following this, the curd is moulded into shaped blocks or balls and packaged for consumption.

“One critical step in mozzarella manufacture appears to be when the curd is heated in a salty water bath, taken out and repeatedly compressed and stretched in one direction,” Ms Pax said.

“This was traditionally done by hand, but industrially this process is replicated using two large screws that push and stretch the curb attached to them,” she says.

Variables that can affect the stretchability of mozzarella include the type of milk, temperature, pH conditions for the lactic acid bacteria (e.g. if the pH is too low, the whey becomes fattier); mechanical forces, e.g. machines stretching cheese, the saltiness of the brine.

The research group is comparing samples from different manufacturers and looking at the microstructure of the different products.

They say the microstructure gives a good indication of the changes occurring in the cheese.

In mozzarella the protein strands are lined up, and it is believed that this kind of microstructure is related to the stretching.

If so, it would be in contrast with cheddar cheese, which has a microstructure more reminiscent of a web, where the fat is more evenly dispersed.

Formal results are expected soon.