Various peppers, fresh, dried and powdered, plenty of capsaicin on this photo

What Makes Food Spicy? – The Science of Capsaicin and Peppers

Ever unknowingly took a bite or big sip from a dish or a newly developed product and suddenly had your mouth on fire? Scrambling to find a glass of water (even though it doesn’t really help), some yogurt, a piece of cucumber, or just anything to help cool your mouth down?

It’s probably overcome a lot of us. Luckily, after a few seconds, or minutes, that heat starts to go away again. Until we take a second bite from that meal. Some of us love the sensation of heat, others can’t stand it at all.

So what is it that makes your mouth feel like it’s on fire?

What makes a food spicy?

If something is spicy, you will notice it thanks to a set of receptors on your tongue. If these TRV1 receptors, are activated, they send a signal to your brain which causes you to feel the heat in your mouth. This process is actually the same as the activation of other pain sequences in your body.

You can get used to some level of spiciness. Over time, and when you continue to eat spicy food, the receptors get desensitized. It is why some people can tolerate a lot more heat than others!


In order for the receptors to get activated and for you to feel that heat, your food needs to contain certain molecules. These molecules ‘fit’ well onto the receptor and trigger the heat and pain response.

The group of molecules that can trigger these spiciness receptors (or pain receptors) are capsaicinoids. It’s a large group of molecules with each a very similar molecular structure. The most potent of them is a molecule called capsaicin.

capsaicin - Source Wikipedia
Capsaicin, from Wikipedia

Other capsaicinoids have a similar molecular structure. Especially the structure shown on the left in the image above is important for activating the receptors. The right side of the molecule can vary quite a bit between capsaicinoids. The exact structure influences the spiciness of the molecule. A slightly different structure can result in a large difference in spiciness. Capsiate for instance, which you’ll find in bell peppers, is not spicy at all. Dihydrocapsaicin on the other hand is very spicy. As you can see

Spiciness doesn’t just affect the tongue

Even though spiciness is mostly tasted in your mouth, it can affect more than just your tongue. If you’ve ever (accidentally) fried hot (dried) peppers in hot oil, you might have noticed that you started coughing vigorously or started to get teary-eyed. This is because the capsaicin can also trigger receptors in the nose and lungs.

If you’re frying up spices, don’t add the dried peppers until the very end, or when you’ve added water as well. If not, you might just accidentally pepper spray yourself (unfortunately, I speak out of experience, having pepper sprayed myself with cayenne pepper flakes roasting in oil)! When you’re using fresh peppers you’ve got a bit more leeway since the moisture in the peppers will prevent them from becoming too hot, too quickly, although they can ultimately also result in a a lot of coughing and tears.

Pepper spray is spicy

Pepper spray is a spray made up of capsaicin. The peppers don’t just impact the mouth, but also your eyes and airways. As a result, you can’t see for a while after being sprayed with pepper spray or you might have trouble breathing.

Capsicum contain capsaicinoids

Capsaicinoids are naturally present in the fruit of plants that belong to the capsicum genus. There are thousands of different cultivars of capsicums grown worldwide. Not all of these are spicy, but the vast majority contain at least some capsaicinoids. Cayenne pepper, bell peppers, chipotle peppers, bird’s eye chili, fresno peppers, poblano peppers, they are all capsicums. Capsicums are thought to contain these capsaicinoids as a defense mechanism against unwanted species.

The black pepper and Sichuan pepper, depsite also being called pepper, do not belong to the Capsicums. They also don’t contain capsaicinoids.

There’s quite a lot of capsaicinoids and capsaicin on this photos. Dried chili and cayenne powder, dried pepper flakes as well as some fresh peppers. Don’t be fooled by their size, some of those green ones are super spicy!

How to measure spiciness?

Since spiciness is very subjective and everyone perceives it differently, it is challenging to measure spiciness using human tasters (as you do for sweetness). Also, people can only test so many spicy samples at the time.

Scoville Unit Scale

Nevertheless, using human testers is still a commonly used method. The Scoville unit scale uses human testers to determine and compare spiciness. This scale, developed back in 1912, uses tasters to determine how spicy a pepper or mixture of peppers is. Tasters get a series of dilutions of a specific pepper. At a certain point, the pepper is so diluted that the tasted can no longer perceive it. The number of dilutions required is the measure for spiciness.

By comparing the results of different peppers for the same person, you get a decent comparison. However, it isn’t the most accurate because of the human error we just mentioned.

Peppers with a score of 0 aren’t spicy at all. The spiciest peppers known have scores of over a million in Scoville Units. For perspective, a mild banana pepper has a score of 100-1,000, a Jalapeno pepper is 2,500-10,000 whereas Tabasco pepper is 25,000-50,000. Commercial pepper spray has a score of over 1 million units.

Spicy pineapple hot sauce

High Performance Liquid Chromatography

Nowadays, tasters are no longer need to test for the spiciness of a food. A more objective method has been developed since using high performance liquid chromatography. Chromatography is a widely used analytical method to quantify the presence of all sorts of molecules. In the case of spiciness you can use it to measure the concentration of all capsaicinoids in a food.

This method has allowed researchers to compare the heat of a wide variety of peppers quite efficiently. If you’re trying to grow a very hot pepper, or the opposite, one that isn’t too hot, this method can give you an objective measure of the pepper you’ve grown and tell you whether you’re on track.

Since pepper suppliers and manufacturers still commonly talk about spiciness on the Scoville unit scale, the results of HPLC are often used to calculate a Scoville value. Every increase of concentration of capsaicin by 1mg/kg causes an increase of 15 units on the Scoville heat scale.

Not all peppers are created equally

The difference in spiciness is considerable between different varieties. Some will inevitably set your mouth on fire whereas for others you won’t feel a thing. If you don’t have access to data on the spiciness of your pepper, it is best to look up your pepper to see where approximately falls on the spiciness scale.

Interestingly though, even within a variety of pepper types, the degree of spiciness can vary considerably. From personal experience I can tell that Jalapeno peppers, even from the same plant, can vary considerably in their heat. For other peppers, the growing conditions can impact the spiciness of the pepper.

Plant’s access to salt and water

A possible factor of influence is the amount of water or salt a plant received during its flowering stage. Some species make more spicy peppers when they’ve been subjected to a drought. Also the amount of salt in which the pepper plant is grown can be of influence.

Changes during storage

Ever after growth and harvest the spiciness of some peppers can change. Some claim that Jalapeno peppers become spicier over time during storage.

It is well known that if oxygen and capsaicinoids come into contact that can result in a decrease of spiciness due to oxidation reactions. The same goes for canning and freezing peppers. Proof has been found that in certain instances it impacts spiciness.

When manufacturing products with peppers these are all factors to take into account. If you want to produce a super spicy condiment, you should take care your process does not influence the spiciness too much.

Seeds and Pith vs. Skin

Capsaicin isn’t distributed evenly throughout a pepper. The concentration of capsaicin is a lot higher in the pith, the white structures within the peppers that connect the seeds to the outer skin of the pepper. By removing these whitish parts, the heat of the pepper is reduced significantly.

Various peppers, fresh, dried and powdered, plenty of capsaicin on this photo

Lowering the heat

If you do happen to eat a very spicy pepper that threatens your food by burning the inside of your mouth, there are a few things you can do. First of all, water won’t help you here. Capsaicinoids don’t mix well with water and water won’t ‘carry’ them away. All water does is help you temporarily feel a little cooler in your mouth and spread all the spicy molecules all around your mouth. If your hands are covered in pepper, be sure to wash your hands and refrain from touching your eyes and lips anytime soon.

What does work though, is eating dairy products. Milk, yogurt, ricotta cheese, they can all actually help reduce the burn. The casein proteins transport the spicy molecules away.

Do you keep on running in too spicy food though? In that case your strategy might be to just stick with it and try to get used to it. Most of us (although there likely are exception) do get desensitized to spicy food over time!

bowl of pineapple chutney

Spicy pineapple chutney

Yield: 0.3l (12 oz)
Prep Time: 10 minutes
Cook Time: 30 minutes
Total Time: 40 minutes

This pineapple chutney is pretty spicy, although you can tone it down by adding less peppers or removing the seeds. The sweetness of the pineapple and the acidity of the vinegar do make this really well balanced. The recipe is inspired by a recipe by Sarah Tiong from Masterchef Australia season 11.

This spicy condiment works well with a lot of southeast Asian meals (or use it to make a toasty/grilled cheese sandwich!).


  • 5 Thai chili peppers (bird's eye chilis)
  • 2 serrano peppers
  • 1/2 large onion
  • 1-2 cloves of garlic
  • 1 tbsp chopped ginger
  • 30g oil (e.g. sunflower)
  • 1/2 tsp shrimp paste
  • 4cm (1,5 inch) slice of pineapple, peeled and cut into small pieces
  • 80g rice vinegar
  • 1/2 tbsp sugar
  • salt to taste


  1. For a very hot chutney, remove the stems from the chilis and add them to the bowl of a food processor. For a slightly milder version: remove the seeds with the white pith from the chillis before adding them to the bowl of the food processor.
  2. Add the roughly chopped onion, garlic, ginger, and oil (you're adding oil to help fry it in the next step) and process into a fine paste.
  3. Place a pan on a medium heat and fry the mixture until it is well cooked. Refrain from pre-heating the pan to prevent being pepper-sprayed when adding the spice mix to the pan. If you're making the spicy version, this step may cause some coughing because of the release of pepper volatiles in the air. Reduce this by simmering it on a low fire, taking more time, but releasing less of the pepper.
  4. Once the paste is cooked, move it to one side of the pan and add the shrimp paste to the other. Quickly fry the paste for a few minutes, you'll smell it instantly.
  5. Mix it all together and add the pineapple, leave on the stove for another 10-15 minutes, on a moderate heat until the pineapple has cooked through.
  6. Take the mix from the heat and add the vinegar, sugar, and salt to balance out the chutney.
  7. Enjoy with rice and a variety of meat and vegetable dishes. The chutney can be stored in the fridge.


Arrowsmith, Sarah, Egan, Todd P., Meekins, J. Forrest, Powers, Dale, Metcalfe, Marcia, Effects of salt stress on capsaicin content, growth, and fluorescence in a JalapeƱo cultivar of Capsicum annuum (Solanaceae) 83, J BIOS, 1, 1-7, 7, 2012,, link

Paul W. Bosland and Stephanie J. Walker, Measuring Chile Pepper Heat, 2010, link

Eissa, H.E., et. al., Capsaicin content and quality characteristics in different local pepper varieties (Capsicum Annuum) and acid-brine pasteurized puree, 2007, link

Kirschbaum-Titze, Petra and Hiepler, Constanze and Mueller-Seitz, Erika and Petz, Michael, Pungency in Paprika (Capsicum annuum). 1. Decrease of Capsaicinoid Content Following Cellular Disruption, Journal of Agricultural and Food Chemistry, 50, 15, 1260-1263, 2002,, link

Brian Rohrig, Hot peppers Muy Caliente!, Chem Matter, Dec-13/Jan-14, link

Krishnapura Srinivasan, Biological Activities of Pepper Alkaloids, Natural Products, 2013, DOI 10.1007/978-3-642-22144-6_184, link

Michael S. Waite and Andrew J. Aubin, A Modular HPLC System for routine analysis of capsaicin from hot sauces, Waters Corporation Milford, 2008, link

Wikipedia, Scoville scale, link

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