Blue Cheese

Opened blue cheese keeps 1–2 weeks refrigerated. It does not freeze well.

Wrap it in wax or cheese paper, then loosely in a container. Blue cheese is aggressive about transferring its aroma to everything around it, so a container is as much for the rest of your fridge as for the cheese — but do not seal it airtight, since the mold is alive and needs some air.

Keep it away from other cheeses. Penicillium roqueforti spores travel readily and will happily colonize a nearby cheddar.

Freezing destroys the paste, turning it crumbly and dulling the flavor. Blue cheese is one of the worst cheeses to freeze.

Blue cheese is the one case on this site where visible mold is the product rather than the problem, and knowing which mold is which is the whole skill.

The blue-green veining is Penicillium roqueforti (or P. glaucum), deliberately introduced, and the cheese is pierced with needles during aging to admit the air the mold needs to grow inward. Those veins are meant to be there and are entirely safe to eat.

What is not meant to be there: fuzzy growth on the exterior surface in pink, black, or bright green, which is a different organism entirely and means discard. The distinction is that the blue veining runs through the paste in the channels where it was cultivated, while contaminating mold sits on the outside as a distinct fuzzy layer.

Ammonia is the key spoilage signal. A faint ammoniac note is normal in a ripe blue, but a strong ammonia smell means the cheese has over-ripened — proteolysis has run too far and the cheese is breaking down into its components. At that point it will also taste harsh and unpleasantly sharp.

The other signal is texture: a blue that has gone slimy throughout, rather than merely creamy near the rind, is past it. Blue cheeses do soften and grow stronger with time, which is normal; sliminess and overwhelming ammonia are not.