In any event, thousands upon thousands of Roqueforts have since been made by inoculating the cheese curd, made from sheep's milk, with Penicillium roqueforti-a mould-producing substance made from rye bread crumbs-and ripening it in the damp, cool, drafty limestone caves that are peculiar to the district. Other blue cheeses may be made with sheep's, goat's, or cow's milk-chiefly the latter-or a mixture of all three, and ripened in a variety of ways, but the use of the mold-producing penicillium is almost universal. And since 1411 when Charles V1 issued a decree restricting the name Roquefort to the cheese made in the Roquefort district of the Causses, no other "bastard cheese made in bastard caves" (as the people of Roquefort jealously referred to their competitors' products) could be called Roquefort.

Osbert Burdett gives the clearest picture of the caves here:

These caverns end in a natural cleft, which communicates, like a chimney, with the open air. As this upper air is cooler than that in the caves, presumably from the presence of hot springs in the rock, a current of air, humid and cool is available in these naturally warm cellars which enables the cheeses to ripen without evaporation.

Proved that, when the fame of Roquefort had nursed a great industry for export, vast cellars, often several floors deep, were excavated and tunnels made to the ventilating shaft, to multiply the advantages of the caverns. With Roquefort, in sum, the conditions for ripening are more important than the method of making the curd.

It is these caves that makes the difference, that are the reason Roquefort-probably the most imitated cheese in the world-has never been duplicated.