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

Spicy Science – On Capsaicin and Peppers

Ever experienced happily taking a bite from a dish or a newly developed product only to discover your mouth is on fire? That the dish is just a tinge spicier than you expected, even though you’ve prepared it the exact same way as you did last time when it tasted just fine?

Besides the fact that you might have bought the wrong type of pepper (they all look so similar don’t they?), you might have also been unlucky. Not all peppers, even of the same type have the same spiciness. We were even told once that only one in 10 Jalapenos is really spicy. Unfortunately, that specific fact does not seem to ring true, but it’s sure that spiciness between peppers can vary quite bit!

All in all, worthwhile to dedicate some time to some spicy science. What is spiciness? How come peppers are spicy at all? And when are they most spicy? Let’s dive into the world of capsaicin and Scoville units.

What makes a food spicy?

Spiciness is not a taste, like sweet, salty and sour are. Taste are literally ‘tasted’ by special receptors in the tongue. Spiciness on the other hand is felt through pain receptors! Spiciness, literally is the activation of a pain sequence and is felt in a similar way as touch and other pains are.

Within the pain spectrum there are different ways pain can be activated though. Two common ones that you’re probably familiar with are touch (or a physical signal) or a a low or high temperature (a thermal signal). If you hit something or place you hand on a hot surface you will feel that pain coming in. Spiciness on the other hand is not caused by such the signal. The spiciness isn’t actually hot (it can be room temperature or colder!), instead, the pain is caused by a chemical. The molecules that cause you to ‘feel’ spiciness will sit on specific pain receptors in your mouth (or nose) and will make you feel the spiciness. You might think you mouth is burning hot, whereas it isn’t, it’s just that a set of molecules can activate that sensation.


The group of molecules that can trigger these spiciness receptors (or pain receptors), are the so called capsaicinoids. It’s a large group of molecules with each a very similar molecular structure. They need this structure to activate the receptors.

The most potent of them is capsaicin, see below. It’s the group on the left side of this molecule (starting just left of the nitrogen (N) atom) that is essential to test spiciness. The chain on the right side of the molecules can vary quite a bit and these different chains of atoms will change the pungency of the molecule.

capsaicin - Source Wikipedia
The molecular structure of capsaicin. Source: Wikipedia.

Capsaicin is the most potent pungency molecule. Another variation, dihydrocapsaicin also greatly contributes to the spiciness of food, whereas capsiate (common bell peppers) is barely spicy at all.

How to measure spiciness?

Spiciness used to be measured using the so-called Scoville unit scale. This scale (developed back in 1912 already) uses tasters to determine how spicy a pepper or mixture of peppers is. This is done by making a series of dilutions of a pepper. Once the heat can no longer be perceived the amount of dilutions required to do so is a measure for spiciness

Even though the method provided a good first insight and is still commonly mentioned, it isn’t the most exact. There is quite some variation between tasters and after tasting too many peppery solutions, the tasters became less sensitive to pungency. Nowadays, tasters aren’t required anymore to test for the spiciness of a food.

The spiciness of a food can now be analyzed by the use of chemical analysis, more specifically using high performance liquid chromatography. This analysis method allows measurement of the concentration of all capsaicinoids in a food. Using a conversion factor, it does seem to be able to convert this result in a Scoville unit. This is a very common phenomenon in food industry. Even though a method might not be the best available anymore, people have gotten so used to it, it’s sometimes hard to get rid of it.

Nowadays manufacturers require more precise control over the spiciness of their foods. They want people to experience the same sensation every time. A quality check for spiciness will be very useful to see whether the last batch of peppers isn’t a lot hotter than the previous one.

Spiciness analysis & food industry

Nowadays for manufacturers it has become more important to analyze the spiciness of their materials since large manufacturers or fast food companies want to make sure their sauces are always of the same strength. That said though, when browsing the internet for peppers there were barely any sellers who would indicate the spiciness of their peppers.

That said though, the method is more commonly used for pepper spray. Pepper spray is based on the same concepts as chili pepper spiciness and a proper evaluation of strength is important to determine whether the pepper spray is of the right strength.

Also, in the industry itself the analysis of the chromatography analysis is commonly still converted in Scoville units. That seems to be the measure most people and industry are used to. This is quite common in food industry, sticking with methods we know.

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!

Peppers with a varying degree of spiciness

So it’s the presence (or absence) of these capsaicinoids that make a pepper spicy or not. The spiciest peppers have most capsaicinoids and also contain the most potent ones (like capsaicin). A bell pepper barely contains any of the spicy chemical, whereas a Jalapeno will contain some more and some of those small red and green chilis from the photo contain plenty.

What’s more though, the spiciness strongly varies within a type of peppers. One Jalapeno might be moderately spicy whereas the next is a lot spicier! Whether this is one on ten (as suggested by the expert in the intro) does not necessarily seem to be exactly true, but natural variation in spiciness is very common.

How to find the spicy pepper?

If you don’t have access to HPLC or a panel of tasters for your peppers it can be hard to figure out whether a pepper is spicy, except by tasting it. As mentioned previously, the spiciness of a pepper can vary greatly within a species. There are a lot of parameters that can indeed affect this spiciness.

The first factor 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 (source). Also the amount of salt in which the pepper plant is grown can be of influence (source). Thus the growing of peppers will impact spiciness and not always can this be controlled for easily.

But also after growth and harvest the spiciness can change. Some sources claim that Jalapeno peppers for instance become more spicy over time (source). Since the spiciness completely depends on the presence of a few chemical components this could well be the case. If these components can still be formed over time or if they’re broken down, the spiciness will change. A way to reduce the spiciness over time is by mincing a pepper and leaving it open to the air. The oxygen in the air can cause a reaction to break down capsaicinoids (source). The same goes for canning and freezing the peppers, they seem to lose some of their spiciness (source and here).

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.

Lowering the heat

That said, chances are still there you might unexpectedly run into a super spicy pepper that threatens to ruin your food. Luckily there are a few things you should (or shouldn’t!) do. First of all, water won’t help you here. Capsaicin, the most potent spiciness component of peppers does not dissolve in water. So rinsing it off your hands won’t work and also in the mouth water will not stop the spiciness of the pepper.

It is commonly said that milk or yoghurt will help relieve the heat. This indeed is true, dairy products with casein proteins do help to reduce the heat. The casein molecules aren’t only useful for making cheese, when it comes to battling spiciness they bind the capsaicin and prevent it from reaching your pain receptors.

Another way to lower the heat, though be it on the longer term, is to slowly increase the amount of peppers you eat. Over time, people can get used to spiciness and thus eating the same amount of peppers won’t feel as spicy anymore.


University website describing spiciness analysis.

Application note of the use of HPLC for analysis of spiciness.

Nice infographic from ACS on spiciness and peppers.

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