Blue cheese or bleu cheese is cheese made with cultures of the mold Penicillium, giving it spots or veins of the mold throughout the cheese, which can vary in color through various shades of blue and green.
This carries a distinct smell, either from that or various specially cultivated bacteria.
Most blue cheeses are made from cow's milk, but Roquefort is made from the milk of the ewe.
Spores of species Penicillium roqueforti are mixed with either the milk or the curd.