In northern Italy, banks accept wheels of Parmigiano Reggiano as collateral for loans. This episode explains why. The cheese has protected origin status and can only be made in a small area around Parma, Reggio Emilia and nearby provinces. It uses unpasteurized milk heated in copper-lined vats, with rennet, and roughly 1,100 liters of milk go into two wheels. The whey is fed to the pigs that become Prosciutto di Parma, and after at least 12 months each wheel is tapped with a small hammer to grade it.

We cover the Sikh immigrants who made up about 60 percent of the workforce by 2015, and a history that runs from a 1254 Genoa deed to Samuel Pepys burying his cheese during the Great Fire of London. The episode also covers mafia thefts of more than 2,000 wheels, the 2012 earthquakes that damaged around 300,000 wheels, and Massimo Bottura’s recipe to help sell them. We end with the glutamate behind its flavor, US cellulose scandals, and how to spot the real thing.

• How copper vats and rennet turn milk into Parmigiano Reggiano
• The acoustic hammer test and the three-tier grading system
• Why banks like Credito Emiliano hold aging cheese as loan collateral
• How local microbes tie the cheese to its region
• Checking for the dotted rind, and how Grana Padano differs