Is Mold in Blue Cheese Harmful? How to Tell

The blue-green veins in blue cheeses such as Roquefort, Gorgonzola, and Stilton are not signs of spoilage; they are Penicillium cultures deliberately added during production. In this state, the cheese is not spoiled; this is its expected appearance. To tell whether blue cheese is actually spoiled, look for unusual colors and odors outside the blue veins themselves.

What signs indicate actual spoilage?
If pink, orange, or black spots appear on the cheese’s surface, the spots indicate contamination by a microorganism different from the mold culture used in production, so discard the cheese. A thin, wet, sticky layer on the surface is also a sign of spoilage; fresh blue cheese may be crumbly and moist, but it should not be slimy. Smell is another useful measure. Blue cheese naturally smells sharp and slightly sour and may have a trace of ammonia, but if the ammonia smell becomes strong enough to sting the eyes, the cheese may be overripe or starting to spoil. The same rule applies to tasting: a mild sharpness is normal, but cheese that leaves a bitter, soapy, or metallic taste should not be eaten.

What do the packaging and storage conditions indicate?
A swollen package of vacuum-packed blue cheese indicates unwanted gas may have formed inside, so do not eat the cheese. Opened blue cheese is generally a product that should be consumed within 2–3 weeks in the refrigerator; if kept far beyond this period, the white areas around the veins often turn yellow, dry out, and crack. Mold that was not part of production can be harmful on blue cheese too: on firm blue cheeses such as Stilton, cut at least 2.5 cm (1 inch) around and below a small mold spot, then eat the rest; discard soft blue cheeses such as Gorgonzola Dolce entirely. However, if the spots have spread across a large part of the cheese or appear together with the odor and texture signs above, discard the whole cheese. Blue-cheese varieties also differ: Danish blue has denser, sharper veins, while Gorgonzola Dolce has a softer base closer to cream in color. The expected appearance is therefore not exactly the same for every brand; remembering the color and smell when first opening the cheese can make later changes easier to notice. To delay spoilage, remove blue cheese from its original packaging, wrap it in wax paper, and loosely cover it with plastic wrap. Wrapping it tightly can prevent the cheese from breathing and lead to moisture buildup, which may cause unwanted mold. Blue cheese can be frozen, but after thawing it becomes crumbly and less creamy than when fresh, so freeze it only for use in cooked dishes.

The main issue with blue cheese is not the presence of mold but which mold is present and how much. Expected blue-green veining, a mild ammonia smell, and a crumbly texture are normal, while spots of an unusual color, a slimy surface, a stinging odor, or swollen packaging are reasons to discard the cheese safely.