A Planet Cheese reader asked me recently about ammoniated cheese. What causes that unwelcome smell and can anything be done about it? I call it the death rattle because it’s usually a sign that the cheese is not long for this world. Most cheeses give us clues when they’re flawed or heading south; learning to recognize those sensory signals can avert a purchase you may regret. So in this journey to the dark side, let’s take a look at some not-so-nice cheeses and analyze what may have gone wrong. 

Ammonia: First, that ammonia smell. It may be a turnoff but it’s a consequence of aging, especially for bloomy-rind cheeses like Brie. As these cheeses ripen, their surface molds break down protein into amino acids and one byproduct of that breakdown is ammonia. When a Brie is aging at the creamery on a rack, the ammonia is evacuated through ventilation. But once the cheese is wrapped for sale, the gas is trapped. That’s why you smell it most strongly when you first unwrap a cheese, especially if it was enclosed in plastic film. 

Leave the cheese unwrapped at room temperature and the ammonia will likely dissipate. If it doesn’t, the cheese is overripe and you have a casualty on your hands. When you shop, look for a wrap date on the store sticker. At good counters, clerks go through the case regularly and rewrap cheeses that have been in plastic for more than a few days.  

Discoloration: Most cheeses should have a uniform internal color, perhaps darkening somewhat near the rind. But you shouldn’t see internal mottling or washed-out zones. According to Dean Sommer, a senior cheese technologist at the University of Wisconsin, those blanched zones are “acid spots,” and they occur when salt diffuses in the curds too slowly. The result is faded areas with more acidity.

Mold where it shouldn’t be: Natural rinds occasionally develop cracks that molds view as an open door. The fungi grow into the paste (the interior) where they aren’t welcome. You may have seen incursions of white surface mold in the paste of a Brie or Camembert. That’s a flaw. When surface molds creep deeply into the paste of Cheddar-type cheeses, it’s not harmful but it’s certainly unsightly. You can trim it away and safely eat the remainder, but it’s annoying to have to cut out costly cheese. 

Blue veins in Cheddar: In my view, this occurrence is a bit different—and more acceptable—than the major incursions you see in the previous photo. It’s not uncommon to spot a nugget or thin vein of blue mold in rinded Cheddars. Penicillium is in the aging cellar and it finds a pathway into these clothbound wheels. Montgomery’s—the much-admired British Cheddar—often has blueing, sometimes too much for my taste. You can see a bit of it in this image of Montgomery’s from Britain’s esteemed Fine Cheese Company. A little blueing is “quite normal,” according to the Montgomery’s website. “The cheese may be even tastier for it.” 

Internal cracking: A few thin slits in a Gruyère or Comté are no cause for concern. In fact, they’re a sign that a cheese of that type is mature. But big internal cracks are likely caused by gas-producing bacteria—and not the good gas-producing bacteria that create the eyes in an Emmentaler. Cheesemakers call this phenomenon “blowing” and it has multiple causes, from unclean milk or sanitation lapses at the creamery to bacteria in the animal feed. 

Peeling rind:  I had never seen this problem before on a washed-rind cheese (or any cheese, for that matter) so I sent my picture to the creamery. The reply: “Peeling can happen from temperature or humidity fluctuations, usually on more mature rinds. Younger rinds tend to be more cohesive.”

As for the wheel pictured at the top of this post, it’s an excellent Corsican sheep cheese, and those molds are just doing their job.