Many people believe that dark roast coffees have more caffeine by virtue of the fact that they taste stronger. This certainly is not true. Dark roast coffees don’t actually taste stronger at all. They are simply more bitter. Others believe that roasting destroys caffeine and thus light roast coffees have more caffeine. The general consensus among coffee experts is that none of this matters and the difference in caffeine content between light, medium, and dark roast coffee is negligible. What does the evidence say?
Certainly, as most coffee aficionados will assert, there is no exact answer to this question as the caffeine content of coffee depends on much more than just the degree of roasting. The coffee itself, the variety, and where it was grown will influence the caffeine content. Since you are not likely to drink the exact same coffee in both light, medium, and dark roast varieties, under the exact same brewing circumstances, it is not likely there is any generally correct answer. Unless that is, roasting affects caffeine content more or less than we’ve been led to believe.
The Final Answer? Do light Roasts or Darker Roasts Have More Caffeine?
However, after looking at as much evidence as I can possibly stand, I have come to a conclusion: coffee brewed from lighter roasts will tend to have more caffeine than darker roasts. This is something we believed to be true for years and it does seem to be the truth. Will this make a big difference to you, the coffee drinker? No, given all the variables, the difference in the amounts of caffeine is negligible. To someone who does not drink a lot of coffee or anyone more sensitive to caffeine, a dark roast coffee may be a slightly better choice.
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Scientific Evidence of The Influence of Degree of Roasting on Caffeine Content in Coffee
There have been dozens of studies looking into the effects of roasting on the caffeine content of coffee. All of these studies have different methodologies, different brewing methods, etc. One of the biggest problems is a lack of standardization or agreement about how to quantify different degrees of roasting.
In 2011, a study published in Food Chemistry found that, among the coffees tested, “Light roasted Cherry coffee contained the highest overall content of caffeine among all coffees, which exhibited a decrease with intensified roasting.” 1 A study from 2013 by Tfouni et al. found that, among the two coffee cultivars they tests, a light roasted coffee had the lowest caffeine content. 2 Another study by Cwikiva et al. found that degree of roasting had no effect on caffeine content. 3
Mixed Results and No Consensus
These, among many others, exhibit the typical kind of results we’ve been seeing for years, results that show absolutely no agreement. Since for years, all that has been available is conflicting results and rampant disagreement from study to study, some coffee experts have thrown up their hands and declared that roasting must not matter much. However, when all the evidence is conflicting, this is not, in itself, evidence. It is just a sign we need better studies.
Regardless, none of the scientific evidence has helped pin down whether and how roasting effects the caffeine content of coffee. As demonstrated by the results discussed above, some studies have found that light roasts have more caffeine, and others that darker roasts have more caffeine. However, the most commonly reported result is that caffeine content is unaffected by roasting, and this is what most experts have been repeating in recent years.
New Robust Investigation Into Roasting Effect On Caffeine Content
A study by Lindsey, et al. published November 25, 2024, called “Caffeine content in filter coffee brews as a function of degree of roast and extraction yield” 4 sought to solve these problems by carefully and meticulously documenting and quanitifying each step of the experimental process.
In this study, 30 unique combinations of green coffee variety, degree of roast, and brew time were investigated regarding extraction yield and caffeine content. This is a much more robust sampling than previous studies. An AeroPress brewer was used to prepare brew samples using a 15:1 mass ratio of brew water to ground coffee.
Refractometry and HPLC were respectively used to measure extraction yield and caffeine content of brewed samples. Scanning electron microscopy was used to measure porosity of roasted seeds and showed increasing porosity with the degree of roast. Extraction yields generally decreased for roast batches with roasting mass losses greater than 12–14%, and caffeine concentrations in 10-min brews decreased for roast batches with drop temperatures greater than 400–420 F.
Under identical brewing conditions, caffeine concentrations in brewed samples were generally lower for dark roasts than light and medium roasts. However, at identical extraction yields, dark roasts generally exhibited higher caffeine concentrations than lighter roasted coffees. It is likely that the volatilization or decomposition of soluble compounds and increased porosity due to roasting act as competing mechanisms that determine compound concentrations in resulting brews. 4
A natural process (dry-processed in the sun) Ethiopian green coffee (Organic Chelbesa Raised Bed—Crown Jewel CJO1503) and a fully washed process (wet-processed to remove outer fruit before fermentation) Ethiopian green coffee (Ethiopia Yirgacheffe Grade Zero Washed Adame Kebele—28183) were used in the study. All the coffee was obtained from the same supplier. Roasting method and grind size were carefully controlled and the degree of roasting was characterized by color (via reflectance spectroscopy), density, and percent of mass decrease.
The brewing method was chosen to be relevant to general coffee drinkers but the brew parameters were also carefully controlled and repeatable. The brews were characterized using a handheld refractometer to measure total dissolved solids before mathematically determining the extraction yield. High-performance liquid chromatography was used to measure caffeine concentrations for all brewed samples.
Caffeine Content Lower For Darker Roasts
The study found that if darker roast coffee batches can be extracted to the same extent as lighter roast brews, then caffeine content in darker roasts will be lower. However, darker roasts typically have lower overall extraction yields, thus the caffeine content was generally seen to be lower for darker roasts. And, as the degree of roasting reached extremely high levels, caffeine levels decreased. What this means, in lay terms, is that even though it is possible to get similar caffeine content from darker roasts, we cannot achieve this in with the typical methods we use to brew coffee.
Some Caffeine Lost During Roasting Process, but Nothing Significant
While caffeine does “burn off” during roasting, the study found that roasting itself does not play a large role in the loss of caffeine, and caffeine value, at some point, begins decreasing with increasing degree of roast. However, while the results indicate that caffeine did leave the coffee seeds during the roasting process, this effect did not become significant until a temperature of approximately 400-420° F was reached. Therefore, extraction yield plays a bigger role on the caffeine content of brewed coffee than the degree of roasting alone. As said, extraction yields generally decreased with increasing degree of roast:
Extraction yields were generally observed to decrease with increasing degree of roast for roasting mass losses greater than approximately 12–14%. Darker roasts showed a tendency to require lower extraction yields to achieve identical caffeine concentrations as lighter roasted coffees. This is likely due to higher relative concentrations of other compounds (that contribute to TDS and extraction yield measurements) present in lighter roasts that either decompose or volatilize as roasting progresses. However, decreased extraction yields observed for darker roasts resulted in lower caffeine concentrations than light and medium roasts (under identical grind and brew parameters). Since the range of extraction yields was constrained by a finite selection of brew times and grind distributions, no universal conclusion can be made for all possible degrees of roast and extraction yields. However, data collected in this study show a clear relationship between degree of roast, extraction yield, and caffeine content. 5
Verdict: Brewed Light Roast Coffee Has More Caffeine
What does all this mean? While the study did not, and could not, reach any definitive conclusions, it agrees with the long-held assertion that lighter roast coffees have higher caffeine content (when brewed). However, the amount of caffeine in brewed darker roast may make up a greater part of the extracted materials from the coffee. That is, darker roasts result in weaker brews and more of this weak brew is caffeine.
What can we take from this? There will probably be more caffeine in brewed coffees with a light to medium roast and the darker the roast gets, the less caffeine you can expect in the brewed coffee. The extraction method, grind size, etc. will still influence the results.
The study discusses the porosity of the coffee beans. You can think of porosity as how “puffy” the beans get because of the roasting. Lightly roasted beans are less porous and more dense, i.e. more pufy, while darker roast beans are more porous and less dense, thus more puffy. The more dense and less puffy the beans, the harder it is to extract caffeine. The more puffy the beans, the more easily the caffeine is extracted. However, as beans are roasted to darker and darker degrees, more caffeine is lost through sublimation (the caffeine is “burned off” as a gas). Therefore:
In general, extraction of caffeine and other compounds in coffee is primarily a function of two competing mechanisms: (1) porosity achieved through roasting that increases efficiency of extraction, and (2) volatilization and/or breakdown of compounds due to the roasting process
As I said before, the caffeine in light roast, medium roast, and dark roast coffees will be different, but the difference is likely negligible. Caffeine extraction in extremely light roasts may be inhibited because of the high density of the beans. But due to the caffeine loss in darker roast and the lighter extraction yield, coffee brewed from darker roasts will generally have less caffeine. Light-medium to medium roasts may yield the greatest caffeine content if the extraction yield is balanced with the lower amount of caffeine sublimation during roasting.
Before I move on, I want to point out that, while important for the study, discussing extremely lightly roasted coffees is somewhat academic as they are often not readily available for purchase and rare on the coffee market.
In lay terms all this means that coffee brewed from darker roasts will probably have less caffeine while coffees brewed from lighter roasts will have more. If you are a habitual coffee drinker or take in a lot of caffeine from other sources, these differences will simply not matter to you. For occasional coffee drinkers and those who are sensitive to caffeine, I do believe that a darker roast may be a better choice, resulting in less caffeine being consumed with typical brewing methods and times. However, more evidence may provide better understanding.
Dark Roast Coffees are NOT Stronger! They Are Weaker!
This study also shows that dark roast coffees are not stronger! Indeed, they are weaker due to a decrease in extraction yield with an increasing degree of roast (assuming roasting mass losses greater than approximately 12-14%). Indeed, very dark French roast coffees are typically ground coarsely to avoid over-extraction and bitter flavors. Ironically, avoiding a bitter flavor is simply resulting in a weaker brew with a much lower extraction yield. So, while your very dark French roast coffee may taste stronger to you, it is not actually a stronger brew, all things being equal.
I never buy dark roast coffee. I think darkly roasting the coffee ruins a high-quality coffee bean! Especially if I’m choosing to splurge with more expensive single-source coffee, I look for a roast that is as light as possible. This results in the coffee tasting like coffee and not acrid, bitter, charred, Starbucks coffee (sorry, had to go there). Many people, when tasting light roast or medium-light roast coffees think the coffee is not strong enough! In reality, they just are used to the taste of burn and not to the taste of coffee. If you make coffee at home and even if you make Espresso, try a lighter roast. The coffee “movement” called Third Wave Coffee agrees. Part of this high-quality, farmer sourced coffee movement is an emphasis on lighter roasts to bring out the true coffee flavor.
- Ivana Hečimović, Ana Belščak-Cvitanović, Dunja Horžić, Draženka Komes, Comparative study of polyphenols and caffeine in different coffee varieties affected by the degree of roasting, Food Chemistry, Volume 129, Issue 3, 2011, Pages 991-1000, ISSN 0308-8146, https://doi.org/10.1016/j.foodchem.2011.05.059.(https://www.sciencedirect.com/science/article/pii/S030881461100762X)
- V. Tfouni, Silvia A., et al. “Caffeine and Chlorogenic Acids Intake from Coffee Brew: Influence of Roasting Degree and Brewing Procedure.” International Journal of Food Science & Technology, vol. 49, no. 3, 2014, pp. 747-752, https://doi.org/10.1111/ijfs.12361. Accessed 4 Dec. 2024.
- Cwiková, O.; Komprda, T.; Šottníková, V.; Svoboda, Z.; Simonová, J.; Slováček, J.; Jůzl, M. Effects of Different Processing Methods of Coffee Arabica on Colour, Acrylamide, Caffeine, Chlorogenic Acid, and Polyphenol Content. Foods 2022, 11, 3295. https://doi.org/10.3390/foods11203295
Lindsey, Z.R., Williams, J.R., Burgess, J.S. et al. Caffeine content in filter coffee brews as a function of degree of roast and extraction yield. Sci Rep 14, 29126 (2024). https://doi.org/10.1038/s41598-024-80385-3- Lindsey, Z.R., Williams, J.R., Burgess, J.S. et al. Caffeine content in filter coffee brews as a function of degree of roast and extraction yield. Sci Rep 14, 29126 (2024). https://doi.org/10.1038/s41598-024-80385-3