Does dark roast coffee have less caffeine than light roast?

It really depends on how you measure the caffeine. When coffee is roasted the beans lose some water content (somewhere in the 20% range give or take a few percent). At the same time it is losing weight it is gaining size. This leads to a situation that makes answering this question a little interesting.

Assuming all other variables are the same, if you measure by weight you actually have more caffeine in dark roast because the water loss is faster than the minimal caffeine loss during roasting. If you measure by volume you have less caffeine because the beans expand as they roast. This seems to confuse some people so let me restate the above. If you measure your coffee using a scoop you will have less caffeine per cup using dark roast coffee. If you measure your coffee by weight you will have more caffeine per cup using a dark roast. The difference one way or the other is small. If you are buying a cup of coffee and the coffee is measured by weight (common with pre-packed coffee used in many offices and some restaurants) then dark roast will have slightly more caffeine. If you buy a cup and the restaurant measures by volume (common when coffee is fresh ground and measured on the fly) then light roast will be slightly higher in caffeine simply because you will have more coffee grounds. This is really only an issue if you are talking about two identical coffees and even then the differences are small. It is conceivable if you are comparing two available brewed coffees that a difference in varietals between them could make the have as much effect as the roast and the preparation method will almost certainly had a larger effect than the roast level or varietal. If there is a Robusta in one of the coffees it is almost guaranteed to have more caffeine. This is mostly an academic discussion because the differences in caffeine content are relatively small.

 

Comments

I like this very much

My husband and I have been having this very same conversation for over the last year. He's been telling me that the lighter roast has more caffeine in it. While other people have either agreed or disagreed. And I have a really good friend who has worked at Starbucks for a long time and been to many training seminars involving such topics. And when I asked him, I honestly can't remember what it was that he actually said. But I do know that whatever it was it still did not really answer my question. So when I was in a debate with a roommate this morning (my husband is out of town for work so he was not involved) I decided to get back online and try do some research on it and see what I could find. I will say that your article is the best one that I have read. It explains everything so clearly and it make it much easier to understand. I was finding it very hard to understand how one or the other would have more caffeine than the other either way. So thank you for your article. It was very helpful and I'm actually going to send the link to my husband so he can read it. I think he will like how you explained it as well. Thanks. 2013-07-21

not liking the blond veranda

not liking the blond veranda roast from starbucks. some people still believe that caffeine response is all in a persons head. I got the blond k-cup with expectation of less caffeine response not more. didn't know anything about the length of roasting time having anything to do with it. I just thought it would be a lighter brew. mega heart palp reaction and not in my head. I have less reaction to the expresso brews and dark brews.
 

dark coffee is easy for the stomach

If not anything else, recent research shows that roasting the coffee seeds more results in a chemical that reduces the formation of acid in the stomach. This means less heartburn with dark coffee.

...

did you actually read the original post? Why would you order a blonde at Starbucks expecting a "lighter brew"? What does that even?

Caffeine content

It was my understanding that as you roast coffee longer, the oils come out from the center of the bean and that is where the caffeine is stored, quite a bit of the caffeine burns off or is lost in the oil. This has always been the case for me, I get a caffeine jolt on light roast coffee but not on dark roast.

Grammar Hammer

Hey grammar freak, I can't believe you took the time to point out 'loose' vs. 'lose'.  We all knew what he meant.  What a looser!  :)

Easily Riled Or What

Hey grammar freak, I can't believe you took the time to point out 'loose' vs. 'lose'.  We all knew what he meant.  What a looser!  :) Namecalling, even if it's 'kind of' a pun, is not cool with most people past middle school.  If a simple grammar correction provokes you to hostility, then there are certain places where your time would be far better spent.  

Measuring ground not whole beans

What if you grind the beans before measuring? Though the individual beans may be different sizes between light and dark roast of the same varietal, once ground, the grinds would be the same size. If my understanding of this article and my logic are correct, I take it the dark roast would have slightly more caffeine than an equal measure of light roast?

Measuring ground not whole beans

Yes, I was wondering this as well. Could somebody please clarify whether measuring a scoop of grounds would have an affect on this article's hypothesis?
I believe that the dark roast would actually have more caffeine in a brewed cup, because if you are filling a measured scoop with ground beans, as opposed to whole beans, the packing efficiency would be much improved. With the packing efficiency of ground coffee, the different sizes between dark and light roast whole beans would be inconsequential because they are both ground, right? Therefore, the ratio of caffeine to weight would be more important that volume.
Am I wrong?

Nice explanation, but...

the present tense form for the verb where something is lost is 'lose', not 'loose', which is something you might do to a knot.  This is in spite of the current internet trend to spell it 'loose'.

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