So how does blue cheese get its blue?  With a fungus known as Penicilium roqueforti. Conventional cheesemakers add blue to their cheeses by introducing freeze dried, lab raised spores of roqueforti to their milk. But how did cheesemakers sing their blues before the days of DVIs?

Well it turns out that roqueforti not only makes cheese moldy, but also bread.   Bread, however, plays host to dozens of species of fungi that also makes it moldy...but that’s just the case with commercial yeasted bread. Sourdough bread, naturally resistant to most fungi because of its acidity, is perfectly suited to the growth of roqueforti.  And when introduced to sourdough bread, spores of penicilium roqueforti will consume it, and turn it blue, just like cheese. That blue bread can then be used as a source of spores for making dozens of different blue cheeses. Find out more about the process of growing your own blue fungus in The Art of Natural Cheesemaking