Blue cheese is mould-ripened cheese shot through with blue-green veins of the fungus Penicillium roqueforti, which grows inside the paste and turns a mild fresh curd into something pungent, salty and powerfully savoury. The veining tastes sharp and peppery; the paste around it is creamy to crumbly, smelling of mushrooms, butter and barnyard. The family spans the sheep's-milk Roquefort of France, the cow's-milk Gorgonzola of Italy and the Stilton of England — each protected, each unmistakably "blue."