Whether you find the odor delightful or despicable, it’s good to know why some cheeses can fill a room with stank.
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If you’ve ever purchased a few wedges of cheese from Whole Foods, left them in your car to run a quick errand, and return to find your car smells like a gym sock, you know all too well how quickly—and how strongly—some cheeses can smell.

For some, the stench is enough to keep them far, far away from the Taleggio. For others, it’s the (dare we say it?) sexiest thing about the ooey-gooey blocks of stinky Epoisses de Bourgogne.

Why cheese stinks comes down to one thing—or rather, billions of things: bacteria.

Why Cheese Stinks

To make their product, cheesemakers add starter cultures of bacteria to milk. These special bacteria help break down the lactose sugars in milk and turn them into lactic acid. Then, cheesemakers add rennet, a group of enzymes that make the milk curdle or coagulate. This produces curds and whey.

With the first curds, cheesemakers cut and cook and heat and smash to get out as much whey as they possibly can. The curds are then pressed into a big lump, salted, and stored for weeks or months to ripen and become the food we love so dearly.

Since all cheese starts with milk, whether it’s cow, sheep, or goat, the thing that makes each batch unique is the starter bacteria that are used. Indeed, the type of starter culture largely determines the taste, flavor, and texture of the final cheese result.

The starter culture is also what makes stinky cheeses so pungent.

Most of these cultures include one particular type of bacteria that’s exceptionally great at ripening cheese: Brevibacterium linens.

B. linens, as it’s called for short, is the same bacterium that is responsible for—and here’s the part where you might want to brace yourself—human body odor. Yes, indeed, there’s a reason that stink reminds you of a high school locker room.

It’s often combined with other bacteria to create unique and proprietary culture blends. Some starter cultures produce mushroom-like flavors that are musty and earthy. You might find them in Brie and Camembert. Others produce fudgy, briny, almost meaty flavors. These may be used in blue cheeses.

Watch: WTF is Bleu Cheese?

Washing Adds Stink, Too

As cheeses age, cheesemakers also introduce another funk factor: washing. Aging certainly intensifies the aromas made by the bacteria, but washing the cheeses is the cherry on top of the odor pile.

Cheese rinds, or the edges of the cheese blocks, are often washed to help the cheese ripen and to keep the cheese moist while it sits. The type of wash that’s used depends on the cheese that’s being made and the cheesemaker’s preferences. Beer, wine, liquor, salt water, or just plain water may be used. The introduction of these washes to the bacteria-busy rinds sets up the cheese for even more stank.

But don’t let the stink of a cheese turn you off from eating a wedge (or two) at your next party. Some of the stinkiest cheeses are among the most delicious, and a cheese’s odor is not always an indication of a potent flavor either. (Blue cheese are perhaps the exception to this rule.)

Epoisses de Bourgogne is one such example. It’s incredibly stinky and can fill a room (or empty it, as it were) in minutes. But its flavor is quite mild, especially compared to its smell. It’s mildly sweet with a just-right balance of salty and spicy.

A lot of triple crèmes are the same way. Their rinds carry a particularly powerful odor, but the cheese itself is very mild and sweet.

When a Stink Is a Sign of Bad Cheese

So when a bad smell is actually a sign of a good food, when is a smelly cheese a sign of a bad food?

When it smells like ammonia.

Cheeses that are past their prime will begin to smell like ammonia, a chemical-like scent. If you smell that and notice signs of degradation (breaking down in the rind, tufts of mold, discolored spots on the cheese), you should toss it. This cheese is bad, and the stink isn’t a good sign.