Ask New Harvest: Caffeine in Light Roast vs. Dark Roast

I am very happy to be starting new bi-weekly (when possible) blog posts about YOUR coffee questions!

This idea started recently when a friend of mine tweeted @nharvestcoffee and asked about dark roast coffee.  Many people have heard that dark roasted coffee actually contains less caffeine than light roast.  His question was, if you want lots of caffeine with a dark roast coffee, do you have to add more coffee than usual?

I want to note, as I will with many other posts, that when it comes to coffee, I am not a scientist, nor are many coffee theories scientifically proven.  Even googling this question, you are bombarded with many different theories on this question.  So I would like to answer on a basic level and hope it gives some insight!  

So, the question:

Does dark roast coffee contain LESS caffeine than light roast.

For background knowledge, to put it simply, it is what it sounds like: light roasted coffee is coffee roasted for less time, dark roasted coffee was roasted for longer (hence the smokey, roasty flavor notes).

Let’s not focus on what is going on inside the bean with these different roast levels, and instead, look at the outside, or physical appearance. Light roasted beans are slightly smaller and denser than their dark roasted counterparts, who come out of the roaster slightly more puffed up and lighter in weight.  Think popcorn.

Light roast on left, dark roast on right. 

And here is where our question is “answered.”  Dark roasted coffee beans are larger and weigh less, so if you were to use a 1 cup measuring cup, and scoop out a level 8 ounces of light roast coffee and  a level 8 ounces of dark roast coffee… voila!  There is actually LESS dark roasted coffee in that 8oz cup. Make sense? Although it looks like the same amount of coffee visually, there are less dark roast coffee beans due to their size and density.  If you were to brew those 8oz. samples and test the caffeine levels in the brewed coffee, MORE caffeine would be in the light roast as opposed to dark roast ( because there was actually more coffee in the 8oz. of light roast)

Here’s the thing.  Many places weigh their coffee.  I first encountered this while bagging coffee as a new New Harvester.  A pound of light roasted coffee fit into our one pound bags perfectly, with just enough space to roll down the top of the bag a few times and give it a nice presentation.  However the dark roasts always filled up the bag more, giving you only an inch of wiggle room to roll the bag down to make it look nice.  What’s going on? I put the same amount of coffee in the same size bag! Why is the French roast SO full??

It’s because of what we are talking about here, and it applies  to brewing.  When we brew coffee at New Harvest, we weigh out our coffee whole bean before grinding.  Here is a picture I took of 23 grams of a light roast coffee and 23 grams of a dark roast coffee in a drinking glass, which conveniently had lines on it…

Light Dark

It’s the same weighed amount of coffee, but there is slightly more dark roast coffee in that sample.  Now, if we were to brew these two samples, we would end up getting pretty much the same amount of caffeine in our cups! Because there are “more” coffee beans in our dark roast sample, but that equals the same  weight, so the same amount of caffeine content as our light roasted sample.  

So it’s actually not what is going on inside the bean, but more the fact that the caffeine is more spread out in the bigger, less dense dark roasted beans.  Thinking of it as the amount of surface area helps, too.  And when you are going to most cafes (or brewing at home with a scale!) this would be the result you would be getting : if it is weighed out it is going to be the same amount of caffeine.

Now with most coffee questions, this opens Pandora's box:  but what’s happening with the caffeine inside the bean when roasting?  Or the variety of bean?  What about grind SIZE!? etc, etc.  All of these are valid questions, however, the measurable impact of the caffeine difference will have on your body is tiny.   The most important thing is to enjoy whatever coffee you prefer!  If you are looking for that extra boost, have another cup!

If you have any other coffee questions, tweet them to @nharvestcoffee, or post on our facebook page.  Ana will post a quick response, but it could turn into a whole blog post!

Thanks for reading!