Hot Peppers

This January morning finds most of the United States in freezing temperatures. We’re covered in ice here in Louisiana. It sucks to be you Duluth, MN. I mean, they’re even putting jackets on in San Diego! Get it? It’s cold. So, today’s post is intended to warm you up. Let’s talk about heat, spiciness that is. In the plant world, that means red hot chile* peppers, Capsicum sp. not one of my favorite rock bands. Here’s more than you ever wanted to know about the plants behind the piquant and the chemistry behind the chile.

Cubanelle peppers via Wikipedia

Capsicum plants belong to the Solanaceae family along with tomatoes, potatoes, tobacco and petunias. There are five domesticated species C. annuum, C. baccatum, C. chinense, C. frutescens, and C. pubescens and about 22 wild species. From chili to hot sauce to salsa to creole seasonings, hot peppers are big business in the United States (>$400 million). The top chile producing states are New Mexico, California, Arizona and Texas. It’s not all about the heat though. The Chile Pepper Institute in New Mexico is dedicated to Capsicum research for better varieties- bigger, more flavor, more color, more heat, and more disease-resistance. Not only are they delicious, but the plants thrive in hot, arid climates and provide lots of nutritious beta carotene.


The traditional measure of spicy heat when it comes to Capsicum flavor is the Scoville scale, which was developed in 1912 by pharmacist Wilbur Scoville. In this test, a hot pepper extract is serially diluted in water and a panel of tasters report whether they taste the heat. Scoville Heat Units (SHU) indicate the degree to which a pepper’s extract can be diluted and the hot taste is still detectable. Thus, the higher the SHU, the more spicy the pepper. Obviously, this subjective test depends on the sensitivity of the tasters. Modern tests still report spiciness as SHUs, but the detection is done using analytical chemistry techniques and not panels of tasters. We now know what chemicals in the peppers (more on that below) are responsible for their spiciness, and they can be accurately detected and quantified. These measurements can be converted over to the popularly familiar Scoville scale.

Who’s the hottest of them all?

Jalapenos, Serranos, and even Bird’s eye peppers can all just sit down (5,000 – 100,000 SHU). Even if you’re not a hot pepper aficionado, you may have heard of Habaneros or Scotch Bonnet peppers (100,000 – 700,000 SHU). Nope, not them either. Other hot pepper enthusiasts (or funny Youtube videowatchers) have probably heard of Bhut Jolokia (aka Ghost) peppers, which were the reigning champions of hottest peppers in the world several years ago, checking in at (1 million SHU). The hottest chile pepper tested by the Chile Pepper Institute is the Trinidad Moruga Scorpion pepper (1.8 – 2 million SHU).  The current world record holder for the hottest pepper is a variety called Smokin’ Ed’s Carolina Reaper (2 million SHU) developed by Ed Currie of PuckerButt Pepper Company in South Carolina. Really, I think the variety and company name says it all. Of course, the Simpson’s gave us the hottest fictional peppers (the merciless peppers of Quetzalacatenango).

Capsacinoids and Feeling the Heat

Capsaicin via Wikipedia

The chemical responsible all of this heat is capsaicin and other capsaicinoids. They are alkaloid compounds derived from simple phenolics like vanillin, but much more elaborate. Yes, plants can take you from plain vanilla to superfirehot capsaicin in just a few chemical transformations. I’ll spare you the details of organic synthesis, but the biology is interesting enough to dwell on a moment. Capsaicin binds to and triggers the Transient Receptor Potential cation channel subfamily V member 1 (we’re going to call that TRPV1 from now on). At temperatures greater than about 109 F (43 C), the TRPV1 channel opens and gives us a painful heat sensation, so that we can recognize the pain and avoid the cause of it. Capsaicin binds to this receptor and triggers it to open at lower temperatures, giving us a burning sensation without any real heat.** This property is medically useful and capsaicin can be found in low concentrations in creams to give a warming sensation to relieve muscle and arthritic pain. Humans can build up a resistance to capsaicin by long term exposure to the molecule, for example, by eating hot chile peppers over their lifetime. Tolerance never gets high enough to resist capsaicin spray to the face, which is the active ingredient in pepper sprays. Of course, there are molecules with higher Scoville ratings than even pure capsaicin, orders of magnitude higher. The chemicals resiniferatoxin and tinyatoxin are naturally-occurring chemicals made by the cactus-like spurge plants Euphorbia poissoni. If one were so inclined, you could create a GMO chile pepper that produced these compounds as well, but the resulting fruit would likely be lethal.

Why are they so hot?

Modern plant breeding by humans has escalated the amount of capsaicinoids in some varieties because humans value the novelty of spiciness, but these chemicals serve an important function for the plant. Pepper plants produce these secondary metabolites as a feeding deterrent for mammals. The concentration of capsaicinoids is highest in the white pith along the inner wall of the peppers. Because, you know, most mammalian species are smart enough to avoid eating these plants. Fun fact, outside of an agricultural setting, peppers rely on birds to disperse their seeds. Birds are impervious to the effects of capsaicin (yes, due to differences in TRPV1 receptors). The birds eat the peppers without damaging the seeds allowing them to poop the seeds out elsewhere and ensure propagation of the next generation of plants. It’s a great deal for the plants and also works out nicely for the birds. Mammals, on the other hand, have grinding molars that would crush the seeds when the peppers are eaten. This would be a significant disadvantage for the plants. Since the plants cannot run away from mammalian herbivores, they must resort to elaborate biochemistry for defense.

Growing hot peppers

Since January is the time many gardeners spend their time flipping through seed catalogs, earmarking pages and fantasizing about spring planting, you may want to spend your cold day today considering some of the hot varieties mentioned in this post. Seeds for peppers of many varieties are available from the Chile Pepper Institute, including the Bhut Jolokia and Trinidad Moruga Scorpion peppers. Also check out their section on pepper-growing tips. You can buy seeds for the Carolina Reaper peppers here. I know I’ll be purchasing some of these seeds; stay tuned for a follow up post later this summer to see how they turn out. I’m hoping to create some Youtube-worthy pepper jelly this year!


*I’m using the terminology employed by The Chile Pepper Institute; chile = Capsicum plants and plant parts and chili = culinary dish comprised of peppers, meat, tomatoes and beans. (I realize that some people may be very anti-bean when it comes to the chili definition, but I am not taking a position on that at this time. You get the idea.)

**For those loyal readers that have been paying attention, this phenomenon is similar to the effects of menthol from peppermint extract, which gives a pleasurable cooling sensation by activating a different receptor in our nervous system. Hypothesis: The simultaneous ingestion of cooling menthol along with hot chile peppers may weaken the capsaicin effects. I’m going to put my money on the null hypothesis or that the effect will be amplified in an extremely uncomfortable way, but SuperChef has volunteered to be the subject in the experiment to test this hypothesis.

References and Links:


5 thoughts on “Hot Peppers

  1. Pingback: Hot or Not? Nature vs. Nurture for Hot Pepper Pungency | New Under The Sun Blog

  2. Shari Schmidt

    I live here in Mineral Wells Tx. & I want to know if you can buy the Carolina Reaper peppers at any super markets or fruit & veg. stands

    1. johnnaroose Post author

      Thanks! I’ve spent a lot of my research career working with cyanobacteria. They are under appreciated by the general public, so I like to give them the spotlight here.


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