Colors are all traced to waves of light

Dr. Wendy Sue Universe

Dr. Universe,

Why do some cheeses stink?

— Cody, 11

When you take a whiff of stinky cheese, that smell is coming from one of its very important ingredients: microorganisms.

Microorganisms are so small, you’d need a microscope to see them, but sometimes they give off a big stink. To find out more about stinky cheese, I talked to my friend Minto Michael.

Michael is a professor of dairy science at Washington State University and told me microorganisms do a few different jobs to help make cheese. These microorganisms can consist of bacteria, yeasts or molds, but bacteria are the most important in cheesemaking.

When cheesemakers add lactic acid bacteria to milk, the bacteria help get the milk ready for another ingredient called rennet, an enzyme. This enzyme helps turn the milk from a liquid state into more of a solid that will become cheese.

While the bacteria may do a lot of work to help make the cheese, there are benefits to the job.“These bacteria eat up the milk sugar, milk proteins and milk fat, so that they can get energy and multiply,” he said.

As the bacteria eat to get energy, they can also produce a stinky gas. The gas is made up of molecules. Some of these molecules that include ammonia or sulfur compounds are responsible for the smell in a lot of stinky cheese.

When certain molecules come in contact with receptors in your nose, your brain helps you figure out what you are smelling. Maybe your brain tells you to stay away from stinky cheese — or maybe it makes you want to try it.

Michael told me about some of the most smelly, or pungent, cheeses. One of them is called Roquefort cheese. This is a kind of a blue cheese that gets its odor from a mold named Penicillium roqueforti. If we looked at it under a microscope, we might notice that it is a kind of paint-brush shape. Penicillium in Latin means “painter’s brush.”

Meanwhile, a different kind of bacteria called Brevibacterium linens is responsible for the smell and flavor of some other blue cheeses. Brevibacterium linens is not only the bacteria responsible for one of the smelliest cheeses on the planet called Époisses, but is also the same bacteria that makes the smell of human body odor.

When people make cheese, sometimes they will let it age for a while. For some cheeses it may be two months or even two years before they are eaten. As the cheese ages, the aromas often start to get stronger and stronger. Of course, not all microorganisms produce gases that are stinky.

One of my favorite non-stinky cheese varieties is made at Washington State University. It’s a sharp white cheddar called Cougar Gold that comes in a can.

After investigating your question, I was curious to find out what kind of bacteria is in this cheese. It turns out the answer is a top-secret recipe even I’ll never know. But it’s no secret that it tastes and smells delicious.

Have a science question? Ask Dr. Wendy Sue Universe, WSU’s resident science cat and writer, by email at Dr.Universe@wsu.edu.

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