Dear Dr. Universe: What makes a pepper hot? -Christian, 12

Dear Christian,

If you’ve ever eaten a chili pepper, you know it can make you feel really hot. You might start sweating, get a runny nose, or even cry.

Like you, my friend Courtney Schlossareck is also very curious about spicy foods. She is a graduate student at Washington State University and part of her research involves finding out how well people can taste chili peppers in cheese.

When I told her about your question, she said that chili peppers are hot because they contain a particular molecule that brings the heat. Molecules are made up of building blocks called atoms. The molecule in spicy peppers is called capsaicin (kap-SAY-sen). It can add different sensations to the foods we eat.

Peppers come in colors like orange, green, yellow, and red, and have different amounts of spiciness. They can be dried into flakes, ground into powder, or made into a fiery hot sauce.

At the WSU Creamery, cheesemakers have come up with a few cheeses that have a spicy kick. My friend John Haugen, the creamery manager, said some of these cheese recipes include jalapeno peppers, cayenne peppers, and even spicier ghost peppers.

He explained that we can measure how intense a chili pepper’s heat is by using the Scoville Scale. A jalapeno pepper is only 2,000 to 5,000 Scoville units—about the same as tabasco sauce. Capsaicin in its raw form is about 16 million Scoville units. The ghost pepper is about one million Scoville units.

Haugen and Schlossareck said that when we eat a chili pepper, capsaicin molecules land on the receptors in our mouth. Our receptors are little bundles of fibers that transmit different sensations to the brain and around the body.

Our nerves help us feel all kinds of things, including a bit of pain from chili peppers. They can also trigger our eyes to water or make us sweat. Some people really enjoy eating chili peppers, while other people think they are just too hot.

Some scientists think the spiciness of chili peppers might be a defense mechanism to keep too many animals from eating them. Most mammals do stay away from spicy peppers. But in a recent study, researchers found that, in addition to some humans, the tree shrew seems to like hot peppers, too. Some kinds of birds will also eat chili peppers and help spread the seeds.

Schlossareck reminded me that there are lots of compounds that can add different traits to our food. While chili peppers are hot, other compounds can make our mouth feel cool. One of these compounds is called menthol. It comes from the peppermint plant.

Do you prefer peppermint or chili pepper? What about your family and friends? Why do you think people have different tastes? Send us your ideas at Dr.Universe@wsu.edu.

Sincerely,

Dr. Universe