Sardinia's infamous 'rotten cheese': a sheep's-milk pecorino deliberately left open to the cheese fly, whose larvae digest the paste over months into a soft, weeping, intensely pungent cream. A genuine pastoral tradition and a candidate for protected status, it is barred from open commercial sale under EU hygiene law yet survives, spread on flatbread with a glass of Cannonau.
A pastoral cheese found across Sardinia under many dialect names, among them casu frazigu, casu martzu and casu modde, and mirrored on Corsica as casgiu merzu. It begins as an ordinary sheep's-milk pecorino left open to the cheese fly Piophila casei, whose larvae ripen it over months. Guinness World Records has listed it as the world's most dangerous cheese, for the theoretical risk of surviving larvae. Its sale is prohibited under Italy's 1962 food-hygiene law and EU hygiene regulations; even so, the Italian Ministry of Agriculture has entered it among the nation's traditional agri-food products, a listing that grants traditional production a partial derogation, and a protected-designation-of-origin application has been lodged. A 2005 project with the University of Sassari to raise the fly under controlled conditions stalled, and an unofficial trade quietly persists.
The paste is soft to nearly liquid, glossy and weeping, with a heat that builds on the tongue: ammoniac, spicy, and far sharper than any gorgonzola, trailing a long barnyard pungency. Spread thin on moistened pane carasau, its richness is cut by the wine; the boldest eaters leave the larvae in for a faint, mobile pop.
Production begins as a standard pecorino: raw sheep's milk is coagulated with rennet near 35°C, the curd cut, lightly cooked, salted and pressed into a wheel that ages a few weeks. The rind is then opened and the surface moistened so the paste softens and begins to weep oil, an invitation the cheese fly Piophila casei accepts in warm summer air, laying eggs in the cracks. The hatched larvae, a few millimetres long, tunnel through the paste secreting digestive enzymes: lipases that cleave the milk fat into free fatty acids, and proteases that break casein into peptides and amino acids. This accelerated lipolysis and proteolysis turns firm cheese into a soft, homogeneous, straw-yellow cream with its ammoniac pungency and weeping tear, while the larvae's constant movement aerates and blends the mass. Fly activity and ripening proceed best around 20 to 30°C over three to six months; the larvae, able to spring up to fifteen centimetres when disturbed, thin out as the cheese matures, and the chance that a few survive ingestion underlies the food-safety objections.
Variations
Most casu marzu is sheep's-milk, though goat's-milk wheels are also made. The same larval ripening appears across Italy, as furmai nis in Emilia, bross ch'a marcia in Piedmont, salterello in Friuli and gorgonzola co-i grilli in Liguria, and on Corsica as casgiu merzu. At the table some eat the cheese larvae and all; others first seal a portion in a closed paper bag so the light-shy larvae wriggle out before it is spread. It is served on pane carasau, sometimes with crumbled chilli, always with a strong red.
On the Palate
Where Casu Marzu sits in the Italian flavor cloud
Ingredients
Serves 10How it's made
8 steps · 45 min
- 130240 min
Make a young Sardinian pecorino: coagulate raw sheep's milk near 35°C with lamb rennet, cut and gently cook the curd, then salt, press into a wheel, and age it for a few weeks.
Watch outCoagulate the milk right around 35°C — too cool and the curd stays slack, too hot and it turns rubbery before you can cut it.
- 220 min
Pare back part of the rind or pierce the wheel and moisten the surface with a little water or oil, so the paste softens and starts to weep.
- 32880 min
In warm summer weather, set the open wheel in a shaded, airy stone hut and leave it uncovered for the cheese fly Piophila casei to settle and lay its eggs in the cracks.
- 47200 min
Within a few days the eggs hatch and the pale larvae tunnel down into the paste to feed.
- 5172800 min
Let the wheel mature for three to six months, keeping the air humid, as the larvae's enzymes digest the fats and proteins into a soft, weeping cream.
Watch outKeep the cellar air humid through the months of ripening — if the paste dries out, the larvae stall and the interior never softens to that weeping cream.
- 615 min
When the interior has become a homogeneous straw-yellow cream and the larvae have thinned out, lift off the hardened top crust.
- 730 min
Scoop the cream to serve as it is, or first seal the piece in a closed paper bag so the light-shy larvae wriggle out.
- 810 min
Spread the cream on lightly moistened pane carasau, scatter with crumbled chilli if you like, and eat at once with a glass of robust Cannonau.
