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.

[4] Variations of this cheese also exist in Corsica, France, where it is called casgiu merzu;[6] it is especially produced in some Southern Corsican villages like Sartène.

[10] The pecorino is most desirable if made from milk collected towards the end of June, due to the effects of the reproductive cycle of sheep on their lactation, and local fermentation traditions associate higher quality casu martzu with exposure to a warm sirocco wind, which is thought to additionally soften the cheese to encourage further maggot activity.

[11][12] Modern preservation techniques have expanded the cheese's shelf life to several years, where it would previously be unobtainable outside of late summer and early autumn.

[5] 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.

[5] Because the larvae in the cheese can launch themselves distances up to 15 centimetres (6 in) when disturbed,[2][14] diners hold their hands above the sandwich to prevent the maggots from leaping.

[4] 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.

[5] An Italian journalist for CNN described casu martzu's cultural status as "revered", and the unique cheesemaking process combined with the strong, rare taste of the dish are described as icons of the traditional Sardinian pastoral lifestyle.

"[5] Casu martzu is traditionally believed to be an aphrodisiac by Sardinians[18][5] and the shepherding, milking, and fermentation necessary for the dish feature heavily in the island's superstition and mysticism.

[12] Despite this the laws are sometimes not enforced,[5] and 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.

[9] Then it is aged in white wine, with grapes and honey, preventing the larvae from emerging, giving the cheese a strong flavour.