(; literally 'rotten/putrid cheese'), sometimes spelled casu marzu, and also called "casu modde", "casu cundídu" and "casu fràzigu" in Sardinian, is a traditional Sardinian sheep milk cheese that contains live insect larvae (maggots).
A variation of this cheese exists also in Corsica (France), where it is called "casgiu merzu", and is especially produced in some Southern Corsican villages like Sartene.
Derived from pecorino, casu martzu goes beyond typical fermentation to a stage of decomposition, brought about by the digestive action of the larvae of the cheese fly of the Piophilidae family. These larvae are deliberately introduced to the cheese, promoting an advanced level of fermentation and breaking down of the cheese's fats. The texture of the cheese becomes very soft, with some liquid (called "làgrima", Sardinian for "teardrop") seeping out. The larvae themselves appear as translucent white worms, roughly long. When consumed, the larvae can survive in the intestine, causing enteric myiasis.
Fermentation
Casu martzu is created by leaving whole pecorino cheeses outside with part of the rind removed to allow the eggs of the cheese fly Piophila casei to be laid in the cheese. A female P. casei can lay more than 500 eggs at one time. The eggs hatch and the larvae begin to eat through the cheese. The acid from the maggots' digestive system breaks down the cheese's fats, making the texture of the cheese very soft; by the time it is ready for consumption, a typical casu martzu will contain thousands of these maggots.
Consumption
Casu martzu is considered by Sardinian aficionados to be unsafe to eat when the maggots in the cheese have died. Because of this, only cheese in which the maggots are still alive is usually eaten, although allowances are made for cheese that has been refrigerated, which results in the maggots being killed. When the cheese has fermented enough, it is often cut into thin strips and spread on moistened Sardinian flatbread (pane carasau), to be served with a strong red wine like cannonau. Casu martzu is believed to be an aphrodisiac by Sardinians. Because the larvae in the cheese can launch themselves for distances up to when disturbed, diners hold their hands above the sandwich to prevent the maggots from leaping. Some who eat the cheese prefer not to ingest the maggots. Those who do not wish to eat them place the cheese in a sealed paper bag. The maggots, starved for oxygen, writhe and jump in the bag, creating a "pitter-patter" sound. When the sounds subside, the maggots are dead and the cheese can be eaten.
Health concerns
According to some food scientists, it is possible for the larvae to survive the stomach acid and remain in the intestine, leading to a condition called "pseudomyiasis". There have been documented cases of pseudomyiasis with P. casei.
Because of European Union food hygiene-health regulations, the cheese has been outlawed, and offenders face heavy fines. However, some Sardinians organized themselves in order to make casu martzu available on the black market, where it may be sold for double the price of an ordinary block of pecorino cheese. As of 2019, the illegal production of this cheese was estimated as per year, worth between €2–3 million.
Attempts have been made to circumvent the Italian and EU ban by having casu martzu declared a traditional food. The traditional way of making the cheese is explained by an official paper of the Sardinian government.
Casu martzu is among several cheeses that are not legal in the United States.
A cooperation between sheep farmers and researchers at the University of Sassari developed a hygienic method of production in 2005, aiming to allow the legal selling of the cheese.
Because of its fermentation process, the Guinness World Record proclaimed casu martzu as the world's most dangerous cheese.