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Do dark roasts contain more caffeine than lighter roasts?
Many think the roast profile of coffee affects the caffeine quantity of the bean. But is it true?
Published November 5, 2021
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Vasileia Fanarioti
Coffee experts@The Coffee Lab
The answer to this question is not as straightforward as you might expect.
While some people believe that all coffee has a similar amount of caffeine, scientists have found that there are actually significant differences between different kinds of beans depending on how they are roasted and how the coffee is brewed.
For example, darker roast coffees contain more caffeine than lighter ones but the reasons behind that aren’t what you might think.
This post will help break down the facts of dark roasts and caffeine content, so that you can make an informed decision about your coffee choice next time you're at the grocery store.
How do you measure caffeine content?
Caffeine is a naturally occurring chemical that stimulates the central nervous system, and can be found in many different types of food, drinks, and even medicine. There are multiple ways to measure caffeine in coffee, but one of them is using chromatography.
Chromatography is the process of separating the molecules in a compound based on how fast they travel through a medium, where they go to, and what sort of interactions they make. There are many different types of chromatography depending on what you need to separate!
Paper chromatography is excellent at separating out components of mixtures that are water-soluble (like caffeine) from ones that are not (like the rest of the coffee compounds). This method can be used to measure caffeine in coffee but what exactly are you measuring? The roasted bean? Your brew? Depending on your answer the results might be different!
What happens to caffeine levels during roasting?
The caffeine content of ground coffee ranges from 0 to 180 mg per 100 g, which is one range of 90 mg to 315 mg in an average cup of brewed coffee made with 225 g of water.
During coffee roasting, caffeine content does not appear significantly to increase. This contradicts expectations because of the increased weight gained from water evaporation during roasting. The chemical structure of caffeine changes when it is roasted, but no change in quantity is observed. For any change to actually happen, you would have to roast the bean beyond any normal roasting time, thus burning it. Nobody wants that!
So despite what you might have thought up until now, roasting coffee has zero effect on the caffeine content, be it a dark or a light roast.
What happens to caffeine levels during brewing?
Another way to measure if dark roast beans have more caffeine than light roast ones is to brew some coffee and measure the caffeine level .
A simple experiment has been carried out in our lab to show this. 50 mL coffee samples from light and dark roast beans were brewed using a percolator, under standard conditions (100 °C). The caffeine concentration was then extracted with ethyl acetate, and the extract was analyzed by HPLC (High-performance liquid chromatography).
As a result, it can be seen that dark roasted coffee has more caffeine than light roasted coffee, and that's because dark coffee beans are less dense, so there are more beans involved when using dark roast beans.
With the density being less dominant in dark roast beans, it is easier for the water to seep through them when brewing. The result of this is that there's more caffeine in your coffee cup with dark roast beans!
Dark roasts vs. Light Roasts
So now you know that dark roasts have more caffeine than light roasts but probably not due to the reasons you imagined. Now you can correct any of your friends that say they buy dark roasts because they have more caffeine.
The difference between a dark roast and a light roast is the temperature of the beans while they are being roasted. Dark roasts have been heated for longer periods of time at higher temperatures, whereas light roasts have been heated for shorter periods of time at lower temperatures. The process of getting darker or lighter results in a distinct change in flavor for the coffee beans. This is the reason why some people prefer one over the other depending on their tastes and preferences .
Dark roasts have flavour notes of smokiness, charcoal and bittersweet chocolate. Light roasts have more flavour notes of a green herbaceous nature instead of the smoky flavours associated with dark roasts.
One of the most important things to remember is that the roast will affect how you brew your coffee. Something that works fine for one might not work as well for another, which is why it's good to experiment and find what's right for you.
Dark roasting can affect brewing because there is less moisture left in the bean after roasting; this means they are easier to over-extract. There may also be some oil on dark roasted beans, which can cause problems when used in espresso machines. Light roasted coffees, on the other hand, tend to be a bit more forgiving when it comes to the roasting level because there is more moisture left in the bean after roasting.
Final Thoughts
When it comes to the perfect cup of coffee, there are many factors that can affect how your morning espresso or afternoon pick-me-up tastes. The type and roast level of beans you use, whether they're whole or ground into a powder, and even how long you let them sit before brewing, all influence the final product.
And yes, dark roasts contain more caffeine than lighter ones. If caffeinated drinks aren't really your thing but an eye opener is what gets you going in the mornings, I recommend trying out Colombian coffees for their mild flavor while still packing plenty of punch!
About the author
Vasileia Fanarioti
My name is Vasileia and I’m here because i decided to combine my two favourite things: writing and coffee. I love travelling around the world and visiting coffee shops but my biggest goal is to visit a coffee farm, to see where it all starts! You can follow my coffee adventures via my blog: thewanderingbean.net
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