Bubbling blobs of buffalo mozzarella seen steaming atop a pizza as it comes out of the oven — it's a scene tantalizing enough to make almost anyone's mouth water. But what makes this creamy white cheese so delicious?
A new study offers a clue: microbes.
After studying samples of buffalo mozzarella from two dairies in Italy's Campania region, where the beloved water-buffalo-milk cheese originated, scientists revealed that despite subtle variations in how the cheeses were made, they were dominated by the same two groups of microbes: a genus of spherical, chain-forming bacteria known as Streptococcus and a genus of rod-shaped bacteria called Lactobacillus.
And within these broad groups of bacteria, some species were specific to each dairy's cheese.
Related: Do mice really like cheese?
In the study, published Tuesday (Aug. 15) in the journal Frontiers in Microbiology, the authors say the cheeses' processing and raw ingredients give them their distinct microbial profiles, and this likely helps produce their world-renowned taste.
"This study sheds light on the intricate interactions of microorganisms throughout the manufacturing process and fosters a deeper understanding of the craftsmanship behind this esteemed Italian cheese," lead study author Alessia Levante, an industrial microbiology researcher at the University of Parma in Italy, said in a statement.
Levante's team looked at two dairies that make Mozzarella di Bufala Campana PDO, a cheese that must be produced in the Campania region using a specific recipe to earn its "protected designation of origin" label that has been safeguarded by the European Union for 30 years.
To make the coveted cheese, cheesemakers heat raw or pasteurized water-buffalo milk to between 91 and 102 degrees Fahrenheit (33 to 39 degrees Celsius). Then, they add enzymes from the stomach lining of a calf, known as rennet, which break the milk into curds (clumped milk solids) and whey (the leftover liquid). They also add a crucial collection of bacteria, called a natural whey starter, that helps increase the acidity of the resulting curds.
After coagulating into curds, the cheese can then be moved to boiling water to melt together and be made stretchable. The cheesemaker then molds the cheese into shape, places it in cold water to harden and finally puts it in a brine before packaging.
The first dairy in the study was smaller and used more traditional processing techniques, whereas the other, larger dairy used more modern technology. The team took 19 samples of cheese in total and used genetic sequencing to investigate which bacteria were present at each stage of the manufacturing process.
Related: Scientists make yeast-free pizza dough that rises like the real thing
The team found that the pasteurized milk used by the modern dairy added fewer microbes overall and fewer species of bacteria to the production process than the milk that had been "thermized" by the traditional dairy. (Both thermization and pasteurization involve using heat to kill harmful bacteria in milk, but the former uses lower temperatures of around 134 to 154 F (57 to 68 C), compared with 161 F (72 C) for the latter.)
Both dairies' brines, however, were equally rich in microbial species, but not all these species ultimately jumped from the brine to the cheese itself.
Both dairies' natural whey starters were dominated by Lactobacillus and Streptococcus bacteria, and during curdling, these genera were dominant in the cheeses. After curdling, the amount of Lactobacillus increased and Streptococcus decreased in both dairies' samples, likely because the bacteria were no longer exposed to the heat stress that accompanied the stretching process, the authors said.
Because the study looked only at two dairies and a small sample of cheese, the team would like to do a bigger analysis to learn more about how raw buffalo's milk defines the bacteria in the resulting mozzarella and thus makes this type of cheese unique.
In the meantime, the next time you tuck into a slice of pizza or a caprese salad, you can thank the microbes that made it possible.
