Blue cheese is one of the most polarizing foods in the culinary world. To some, its sharp, earthy, and ammonia-heavy aroma signals a rich, savory delicacy. To others, it smells remarkably like gym socks, decaying matter, or spoiled milk. That aggressive aroma isn't a sign that the cheese has gone bad; it is the exact result of the biochemical process that creates it.
The pungent smell of blue cheese comes down to a precise mix of fungi, fatty acid breakdown, and volatile chemical compounds. When Penicillium roqueforti spores are introduced to curd and allowed to grow in oxygen-rich air channels, they trigger a cascade of chemical reactions. These reactions break down fats and proteins into potent odor molecules, turning a mild milk base into a sensory powerhouse. Understanding why this happens requires looking at the specific compounds at play, the role of mold, and how handling and storage influence the final scent profile.
The Role of Penicillium Roqueforti
The defining characteristic of blue cheese is, naturally, the blue-green veins running through it. These veins are colonies of a harmless, specialized mold known as Penicillium roqueforti.
Unlike surface-ripened cheeses like Brie, which rely on white molds growing on the outside, blue cheese molds grow internally. Cheesemakers pierce the wheels of cheese with stainless steel needles during the aging process. This creates microscopic tunnels that allow oxygen to penetrate the dense curd. Further analysis by Bloomberg highlights comparable views on this issue.
Without oxygen, the mold cannot grow. Once air enters these channels, the spores germinate, feeding on the curds and producing enzymes that radically alter the texture and flavor of the cheese. This fungal growth is the primary driver behind both the distinct flavor and the strong odor.
Chemical Breakdown: Lipolysis and Proteolysis
The transformation from milk to pungent cheese happens through two primary biochemical pathways: lipolysis and proteolysis.
Lipolysis (Fat Breakdown)
Milk fat is composed of complex triglycerides. Penicillium roqueforti produces enzymes called lipases, which break these fats down into free fatty acids.
As these fats break down, they release short- and medium-chain fatty acids, most notably butyric, caproic, caprylic, and capric acids. Many of these specific acids are named after goats or Latin words for goatish odors (capra) because they share the exact same chemical compounds found in animal sweat and hair. This is why a fresh wedge of Roquefort or Gorgonzola often carries a distinctly barnyard or bodily scent.
Proteolysis (Protein Breakdown)
Beyond fats, the mold and other accompanying bacteria break down milk proteins (casein) into amino acids through proteolysis.
As these proteins degrade further, they produce volatile sulfur compounds, ammonia, and amines. The presence of ammonia gives blue cheese that sharp, nose-tingling prickle that hits you immediately upon opening the wrapper. While high levels of ammonia can indicate spoilage in other foods, controlled ammonia production is a standard part of the ripening process for aged cheeses.
Key Volatile Compounds Responsible for the Aroma
If you run gas chromatography on the headspace above a piece of blue cheese, a few specific molecules dominate the results.
Ketones are arguably the most important family of odor compounds in blue cheese. Specifically, 2-heptanone and 2-nonanone are produced via the oxidation of fatty acids by the mold. These compounds contribute heavily to the earthy, mushroom-like, and solvent-like notes in the aroma.
Methyl ketones give blue cheese its characteristic spicy and metallic undertones. Esters, formed by the combination of fatty acids and alcohols, add fruity or solvent-like hints that soften the harsher edges of the sulfur and ammonia notes. It is the exact balance of these ketones, fatty acids, and amines that creates the profile recognized worldwide.
Why Some Blue Cheeses Smell Stronger Than Others
Not all blue cheeses smell equally aggressive. The intensity of the aroma depends heavily on milk type, aging time, and geography.
Milk Source
The base milk matters. Cow's milk blue cheeses, such as Danish Blue, tend to be milder, creamier, and buttery. Sheep's milk blue cheeses, like Roquefort, are typically sharper, tangier, and far more pungent because sheep's milk has a higher concentration of medium-chain fatty acids. Goat's milk blue cheeses occupy a similar space, packing a sharp, earthy punch due to high caproic acid content.
Aging Conditions
The length of aging directly correlates with aroma intensity. Younger cheeses have had less time for lipolysis and proteolysis to occur, leaving fewer free fatty acids and volatile compounds in the paste. Longer aging allows mold colonies to thoroughly digest the interior, resulting in a drier, crumbly texture and a much louder scent profile.
Common Storage Mistakes That Ruin Blue Cheese
Because blue cheese contains active cultures and high moisture, improper storage can throw off its delicate chemical balance, turning a pleasant pungency into an acrid ammonia hazard.
- Trapping in airtight plastic: Plastic wrap suffocates the cheese, trapping moisture and encouraging unwanted bacterial growth or harsh ammonia buildup.
- Storing in the warmest part of the fridge: Temperatures that are too high accelerate fat breakdown past the ideal window, while freezing ruins the delicate cell structure of the curd.
- Ignoring cross-contamination: Blue cheese spores are robust. Leaving a wedge uncovered near mild cheeses like mozzarella or cheddar will result in unwanted mold transfer.
To store blue cheese correctly, wrap it loosely in specialized cheese paper or parchment paper to allow it to breathe while preventing it from drying out. Place it in the warmest section of your refrigerator, typically the crisper drawer, where humidity levels are more stable. For a deeper look at proper dairy storage guidelines, you can review food safety recommendations from the USDA Food Safety and Inspection Service.
Frequently Asked Questions
Is the white or grayish mold on the outside of blue cheese safe to eat?
Yes, generally. Many blue cheeses develop a natural rind or minor surface mold during aging. However, if you spot fuzzy pink, black, or green mold that looks distinct from the intended blue veins, cut it away generously or discard the wedge.
Why does blue cheese smell like ammonia sometimes?
Ammonia is a natural byproduct of protein breakdown during aging. If a blue cheese smells overwhelmingly of pure ammonia, it is usually because it has been suffocated in airtight plastic wrap or has aged past its prime. Letting the cheese sit uncovered at room temperature for thirty minutes often helps vent the trapped ammonia gas.
Does the blue mold spread to other foods in the fridge?
It can. The spores of Penicillium roqueforti are airborne and active. If left uncovered, the mold can easily colonize nearby soft cheeses, butter, or produce. Always keep blue cheese wrapped tightly in its own dedicated container or wrapping.
Can pregnant individuals eat blue cheese?
Health authorities generally advise pregnant individuals to avoid soft, unpasteurized cheeses, including certain artisan blue-veined varieties, due to the risk of Listeria bacteria. However, blue cheeses made with pasteurized milk carry a significantly lower risk. For official health advisories regarding safe food consumption during pregnancy, consult the Centers for Disease Control and Prevention.
