Chile peppers are all hot to some degree, but how hot a pepper tastes depends on a variety of factors, from growing conditions to the palate of the person eating those peppers. To explain the science behind hot peppers, along with good to know and how to grow information is my guest this week is chile breeding and genetics expert Dr. Paul Bosland to share.
Paul, who is also known as “The Chileman,” is internationally known as one of the foremost experts on Capsicum, the genus that peppers belong to, and has published more than 100 scientific papers. In 2019, he retired after 33 years from New Mexico State University, where he was a Regents professor of horticulture. He ran the university’s chile breeding and genetics research program and co-founded the university’s nonprofit Chile Pepper Institute, the foremost research-based resource center for chile pepper information. He also founded the Capsicum Genetics Cooperative and served as the chairman of the USDA Capsicum Crop Advisory Committee.
Paul got his start at New Mexico State University as a vegetable breeder working with cole crops such as broccoli and cabbage. He then worked with asparagus and spinach before trying his hand at chile breeding. He realized he could spend all of his time on chiles and still not answer all of the questions that need to be answered. “I put all my chiles in one basket and watch that basket carefully,” he often says.
The Chile Pepper Institute got its start because — in the days before the internet — Paul and his students would mail out free chile seeds to whoever asked for them. It was slow and manageable for a while, but then the university was inundated with seed requests, all from the same retirement community. It turned out the university had sent seeds to one resident who spread the word to everyone else. That led Paul and the university to formalize the operation and charge a little bit to cover their costs.
Established in 1992, the Chile Pepper Institute served as a source for rare chile seeds, though with the dawn of the internet many of those seeds became easier to find. Today the institute sells pepper varieties developed at New Mexico State University, each with “NuMex” in the name.
The Chile Pepper Institute was originally called just “The Chile Institute,” but that led to many confused people calling the institute about the country Chile, Paul says.
Annually, the institute hosts a conference for pepper growers in its home city of Las Cruces, New Mexico. Not only does the event educate growers on the newest information about chiles, but it’s also the biggest networking conference for the chile industry, according to Paul.
The Origins of Chile Peppers
Nearly all domesticated peppers are of the species Capsicum annuum. Spicy Capsicums are known as chile peppers, and non-spicy peppers are called bell peppers or sweet peppers.
Peppers are native to the Western hemisphere. Paul says Christopher Columbus, on his first voyage to the New World, tried a fruit with a burning sensation that reminded him of the black pepper that they have in Europe. “So he called it ‘pepper,’ and the name sticks.”
The name “chile” comes from the Indigenous root word chil, plus an “e” tacked on by the Spanish when they added the word to their written language. In South America, the Spanish-language word for pepper is aji.
Paul says “chili” with an “i” refers to the state dish of Texas while “chile” with an “e” refers to the plant and the fruit. “We say one’s a bowl of brown and the others are red and green fruit.”
Chiles are one of the few crops that are a vegetable, a spice, a medical plant and an ornamental, Paul points out.
Chile Pepper Heat Profiles
Paul’s favorite chile peppers are somewhere between hot and mild. “I’m in the middle. I’m a medium guy,” he says.
How much heat people can take comes down to their DNA. “We’re all genetically different, and it turns out it’s based on heat receptors in your mouth,” Paul explains. “The more heat receptors you have, the more sensitive you are to chile peppers, so you like them milder, and the less heat receptors you have, the hotter you can take it.”
Chile heat isn’t just heat, Paul points out. He came up with a “heat profile” that has five characteristics:
How fast does the heat come on when you bite into a chile? Rapidly, delayed, or intermediate?
How long does the heat linger? Does it dissipate quickly or does it last minutes or even hours?
Where do you sense the heat? The tip of the tongue? The lips? Mid-palate? The back of the throat?
What is the sharp or flat effect? Prickly heat like pins? Or heat that feels like it’s been brushed on?
What’s the heat level? Mild, medium or hot, in terms of Scoville heat units?
When talking about chiles and how hot and spicy they are, you’ll often hear about capsaicin, but Paul says that’s just one compound found in nature that makes peppers hot. There are 22 analogs to capsaicin, and each has a different effect in the human mouth, he says. Some produce sharp heat, some produce flat heat. And what’s hot to you may not be hot to me, because our genetics are different.
Some of the hottest peppers commonly give a delayed heat response.
“That’s why they’re perceived even hotter than they are,” Paul says. “Because you take a bite, you don’t think it’s so hot, and you take that second bite. Now that first bite delayed heat comes on. And then the second one. It’s there and you’re over the top. You’re just over the top. It builds and builds and builds.”
Which heat characteristics are the most desirable varies from culture to culture and person to person. For example, Paul recalls that the United States was having trouble exporting peppers to Asia. Importers there said the quality wasn’t that good. However, when U.S. growers learned that Asian cuisine uses sharp heat, they found chili varieties that fit that bill, and now the United States exports millions of pounds of chiles to Asia annually.
Sharp heat is nuanced under Paul’s heat profile. It ranges from “slightly sharp” to “incredibly sharp.” Takanotsume (“the claw of the eagle” in Japanese), santaka and Thai chiles, are a few examples of peppers with sharp heat. Paul says any chile of Asian origin will likely have that sharp heat.
The Story of the Scoville Scale
Though most people have heard of the Scoville Scale, which rates the heat of peppers in “Scoville heat units,” fewer know its origin.
The scale is named for pharmacist Wilbur Scoville, who developed the Scoville Organoleptic Test in 1912. He was working for a pharmaceutical company that wanted to standardize a capsaicin-based pain relief cream named Heet.
Scoville gave samples to five taste testers. He wanted to know how diluted the samples needed to be before the testers could no longer taste any heat. So 10,000 to 1 would equal 10,000 Scoville heat units, or SHUs.
The problem with that test is “taster’s fatigue,” Paul says. “You can only taste so much heat before you say, ‘I’m done.’”
Taster’s fatigue is the body’s way of defending itself.
“When you lose the sensation of heat, it’s not because the compound has decomposed,” Paul explains. “It’s because your body has produced endorphins to block this pain that it’s sensing.”
A scientist at New Mexico Tech performed an experiment in which he fed students jalapenos and asked them to tell him when the heat is gone. After they said the heat was done, he injected them with endorphin blockers, and the heat came back.
Now, pepper researchers use high-performance liquid chromatography, in which a machine sees all the molecules of capsaicin and counts them. The parts per million are multiplied by 16 to put the pepper on the Scoville scale, since pure capsaicin is 16 million SHUs.
The Rise of the Super Hots
Paul admits he never thought that “super hots” would take off. Those are the peppers that are unbelievably hot, like the Carolina Reaper.
Bhut jolokia, known as the ghost pepper in the United States, was originally cultivated in India. It is a hybrid of two different species of pepper, Capsicum chinense and Capsicum frutescens. It was the first pepper to surpass 1 million Scoville heat units, and it was a big hit, to Paul’s astonishment.
Paul’s colleague in Trinadad said that Trinadad had even hotter peppers, so the Chile Pepper Institute tested them in 2012. Trinidad Moruga scorpion (Capsicum chinense) was in fact hotter, at 1.2 million SHUs.
Generally, the smaller the pepper, the hotter the pepper. There is a biological reason for that. In most peppers, the heat is found only in what’s called the cross walls or placenta, where the seeds are attached. (The “ribs” of a pepper.) The walls of the fruit do not have capsaicin production, so a big fruit has diluted capsaicin while a small fruit has concentrated capsaicin. In fact, a big pepper may have more capsaicin in total but taste milder than a small pepper.
To determine visually if a chile is hot, you need to cut it open, Paul says. Inspect the cross walls and look for yellow veins. That yellow color comes from capsaicin.
There is a prank called “the pepper breeders trick,” Paul shares. Pick a jalapeno from the garden, cut off a piece of the fruit’s wall and eat it. Then cut off a piece of wall that includes the yellow veins, and give it to someone else. You won’t taste any heat, but the person who just ate the veins certainly will.
Why Some Peppers Are Hotter Than Others
Genetics is the first reason why one pepper is hotter than another. The other factor is the environment. Paul says any stress that the environment puts on a pepper plant will increase the heat of the fruit: too hot, too cold, too wet, too dry.
A mild chile could get to be medium hot after an extremely hot summer. On the other hand, a hot jalapeno could drop down to a medium heat after a cool summer.
The first fruit on a plant is hotter than the later fruit. That’s because plants use what are called “secondary metabolites” to make capsaicin, Paul says. When the plants start to use up the secondary metabolites, the fruit won’t be as hot. However, he says if you pick off the first fruits, the next fruits will get hotter.
While there can be a range of heat among the fruit on the same plant, Paul says the greatest variability is from plant to plant. This happens when plant breeders don’t achieve uniformity. The genetic diversity within a pepper variety can mean some seeds grow into plants with mild fruit and others grow into plants with hot fruit.
The Many Uses of Capsaicin
Paul says peppers likely evolved to be hot to keep mammals from eating them. Birds, he notes, have a symbiotic relationship with peppers. Birds can’t taste the heat, so they eat peppers happily, and they then help the plants spread their seeds.
Capsaicin has a number of applications. It has antifungal properties, it’s added to paint to stop barnacles from attaching to ships, and it’s put on wooden fence posts to stop horses from nibbling on them.
Capsaicin can also deter mammals from eating crops. Paul’s lab did a study in which some lettuce was dusted with habanero powder and some lettuce was untreated. Rabbits ate all the untreated lettuce first, then finally ate the dusted lettuce once they had no other option left.
Capsaicin-based pain relief products work because they stimulate the body to produce endorphins to numb pain. Peppers with lasting heat are used to make topical pain relief products, while peppers with quickly dissipating heat are preferred by the food side of the chile breeding industry because consumers can eat more chiles that way.
Why Pepper Walls Matter to the Pepper Industry
When you buy a bell pepper in the United States, it will most likely be a four-lobed pepper. But in Hungary, Paul says, consumers prefer three lobes.
In the hot pepper industry in the United States, two-lobed peppers are the most desirable. That’s because when they are processed they go flat and can be packaged easily, Paul explains.
When Daring Folks Try Hot Peppers
When eating a pepper, the feeling of heat on your tongue can dissipate quickly — within seconds — or can last for hours. But not everyone will have the same reaction to the same pepper.
Paul recalls a field day back when habaneros were new and exotic. A man bit into a habanero and turned bright red. Two hours later, after the field day was over, Paul saw the man again, and he was still bright red. The man must have had a lot of heat receptors.
You may know the type of guy who wants to eat the hottest pepper on the table to show off how tough he is. Well, that can backfire on him. Paul remembers one instance when an ESPN reporter came to visit the institute to see the hottest peppers. Before he started filming, he was advised not to take a second bite of a pepper. Well, he took a pepper, bit into it, declared it wasn’t that hot, and then took a second bite. A moment later, he lost it. He told the cameraman to cut, and then he grabbed a gallon of milk, which wasn’t enough to soothe him.
Paul finds it funny that young people and adventurous people want to eat really hot chiles “but nobody says, ‘Let’s go to the garage and hit our thumb with a hammer.’”
Paul has met a few people — just three — who have no heat receptors at all. Like birds, they can eat the hottest peppers and not sense the heat in their mouths.
How to Tame Pepper Heat
If you are searching for relief after eating a hot pepper, drink milk. Casein — the protein that makes milk white — attaches to your mouth’s heat receptors and keeps the brain from getting that pain signal.
Ice cream is an even better option because it contains casein as well as sugar, Paul says. In fact, the Chile Pepper Institute offers vanilla ice cream to guests while they try peppers.
Where Pepper Heat Is Felt
Paul advises eating salsa slowly and observing what happens. You don’t want to get caught off guard by peppers with delayed heat, and by eating slowly you can observe where you feel the pepper heat in your mouth.
The jalapeno pepper is the typical pepper that is sensed on the tip of the tongue and the lips. The heat will be sharp, it will come quickly, and it will dissipate quickly. The New Mexico green chili will be felt midpalate. The heat is flat, comes on rapidly and dissipates rapidly. The habanero is delayed and will be felt at the back of the throat.
Starting Chile Pepper Seeds
I’m a pretty darn good seed starter, but pepper seeds seem to beat to their own drum. They like it hot and they take their time. Some seeds will take five days to germinate while others from the same pack take 25 days.
Paul says that while it’s true pepper seeds take a long time to germinate, they don’t seem to rot the way that tomato seeds can. Be patient, he advises. Habaneros, for example, can take three to four weeks to germinate.
Paul attributes the range of germination time to wild genes that the pepper seeds have retained. In nature, seeds don’t want to germinate all at the same time because it may be some time before it rains again. By staggering their germination time, the seeds have a greater chance that some will live to maturity.
If you are feeling impatient, you can check the soil to make sure the seeds are still there, and then rebury them and wait.
The Future of Pepper Breeding
There are some varieties of tomatoes known as non-ripening tomatoes due to their fruit staying green and hard. There are no non-ripening peppers, but pepper breeders would love to develop some. Jalapenos, green chiles and green bell peppers are a few varieties of peppers that are picked before they can mature, so non-ripening versions would be desirable for growers.
Tomatoes turn red in response to self-produced ethylene gas. While peppers have a different ripening system than tomatoes, they will turn red if exposed to ethylene. In fact, fields of red peppers can be sprayed with ethylene gas to ensure all the peppers redden up at the same time.
Green, yellow and purple are all immature colors of different pepper varieties. The peppers may ripen to yellow, orange or red. Red peppers get to be that color from dominant genes, Paul explains. Orange peppers are missing one of those genes and yellow peppers are missing two of those genes.
There are green peppers that stay green and are called “perm-green,” but when they ripen they become soft.
Breeders are also trying to develop peppers that are more nutritious. One new release from New Mexico State University is NuMex LotaLutein, a yellow serrano pepper with more lutein than any other pepper. Lutein is a compound that is associated with eye health.
The Chile Pepper Institute at New Mexico State University is open to visitors every day from 8 a.m. to 5 p.m. The institute’s teaching garden, named for Amy Goldman-Fowler, has more than 150 varieties of chiles. Visit cpi.nmsu.edu for more details.
I hope you enjoyed my conversation with Paul Bosland. If you haven’t listened to our conversation yet, you can do so now by clicking the Play button on the green bar near the top of this post.
What varieties of hot peppers do you grow? Let us know in the comments below.
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“Peppers: Vegetable and Spice Capsicums” by Paul W. Bosland and Eric J. Votava
“The Complete Chile Pepper Book: A Gardener’s Guide to Choosing, Growing, Preserving, and Cooking” by Dave DeWitt & Paul W. Bosland
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