Coffee

A Bit About Caffeine

Summary

The other day I was at a watch party for my beloved Pacific FC football team as they competed in the CONCACAF Nations League for the first time. During the half, all the fellow fans around my table started chatting […]

The other day I was at a watch party for my beloved Pacific FC football team as they competed in the CONCACAF Nations League for the first time. During the half, all the fellow fans around my table started chatting and asking each other what we all did. When it came around to my side, I said “I’m a coffee educator”. There were a few double takes, and then the questions started rolling (indeed, I wrote some down, as I want to answer them in this blog space down the road).

The first question was “is it true darker roasts have less caffeine?” Then a “yeah, and what beans have less or more caffeine?”. Everyone at the table wanted to know. So I gave them the simple answers:

  1. Darker roasts actually contain more caffeine by volume weight than the same coffee if it were a medium or light roast.
  2. Each type of coffee has different levels of caffeine, and even the processing method can affect the level of caffeine, so there’s no accurate answer for that, other than to say robusta coffee has 2 times the caffeine arabica coffee does.

Let’s get into both of these things a bit more.

Darker Roasts have More Caffeine by Weight Volume

Green coffee just starting the roasting process inside a drum roaster.

If we take a broad spectrum of one genus of coffee – Arabica – and even out all the caffeine measurements in the unroasted green coffee bean, the average is about 1.2% of the bean’s weight is taken up by the caffeine molecules. Some can be as low as 0.9%, some as high as 1.35%, but the average is 1.2% in the green coffee.

When coffee is roasted, it loses about 15-30% of its overall weight through various elements releasing into the surrounding air, phase-changing (going from solid to liquid, to gas), and through heat-driven conversion into other elements. If you start with 1000g of green coffee, you end up with about 850g, on down to 700g of roasted coffee, depending on how dark the coffee’s been roasted.

According to Andrea Illy and his doctoral thesis paper turned book, ‘Espresso: the Chemistry of Quality‘ one of the most resistant elements to change, or removal from the roasted coffee bean process is the caffeine molecule. So most of the other elements – fats, lipids, oils, gasses, proteins, fibrous bits – of the green coffee bean get changed in the roasting process, the amount of caffeine – that average of 1.2% in the green coffee, remains more or less intact. 

There are many things going on in the roasting process that affect overall caffeine levels, but the biggest one is the weight loss of other elements in the green coffee while it is roasted, so let’s focus just on that aspect.

Here’s how the math breaks down: Take 1000g of green coffee: it has about 12g of caffeine, or 1.2% of its total weight. Roast that coffee to a light roast, and the finished weight is around 850g. But there’s still roughly 12g of caffeine molecules in that roast, making the caffeine percentage 1.4% now. And if the coffee is roasted to a medium roast, the finished weight might be 800g, with still roughly 12g of caffeine inside, giving a caffeine volume of 1.5% of the total weight. Take it full dark, and now the 700g of coffee – which still has roughly 12g of caffeine inside – has 1.7% of its volume as caffeine.

If we use 35g of roasted beans to brew 500ml of coffee, here’s how much caffeine, by weight, is in those 35g samples:

  • Light Roast: .49g (490mg) of caffeine
  • Medium Roast: .52g (520mg) of caffeine
  • Dark Roast: .6g (600mg) of caffeine

So the darker the roast, the more caffeine is in the coffee.

I do need to point out, I’m oversimplifying things here and leaving out other things that factor in the overall volume (by weight) of caffeine in roasted coffee, and the brewed cup of coffee.

For instance, extraction rates of caffeine in lighter roast coffees are lower (around 92% total extraction) vs darker roasts (about 95% extraction). So if that dark roast had 600mg of caffeine in the coffee, roughly 570mg of it makes it to the cup. But the light roast coffee, with 490mg of caffeine, only delivers about 450mg to the cup, a full 120mg less of caffeine than the dark roast.

Also, Illy in his book said some arabica coffees can contain as much as 2.4% caffeine by volume when roasted, effectively doubling their unroasted caffeine volumes. He goes into great detail about this in the book, so if you can manage to find a copy, it’s well worth diving into.

Don’t even get me started on caffeine’s solubility vis a vis water temperatures. Basically, the higher the temperature, the more caffeine is extracted. This is why cold brew coffees are pretty low in caffeine (and low in taste complexity too, but that’s another article).

What Coffees Have Less (or More) Caffeine

The easiest way to answer this is by talking about the two most common types of coffee: Arabica and Robusta. Across the spectrum of coffees within these two groups, Arabica coffees typically have about 1.2% of their unroasted weight in caffeine. Robusta is almost double, at 2.2%.

That said, there are some robustas with as little as 1.5%, and some with 3% or more. Some arabicas have as little as 0.9%, and some as high as 1.5%. And the same coffee from the same farm one year might have 1.2%, then have 1.35% the next year. So there’s no easy answer here.

Less Caffeine

Everyone these days seems to want less caffeine, so what do you do if that’s you?

A trend today is for some flashy companies to advertise “naturally caffeine free” coffees, or “ultra low caffeine natural coffees” They’re mostly scams or using ultra light roasts (remember, the lighter the roast, the less caffeine percentage is in the coffee), combined with low temperature brewing methods or ultra quick extractions. I’ve seen some compare it to tea. Well, if you want to drink tea, drink tea. We’re about coffee here.

Arabica Laurina out of Réunion Island is interesting, with claims it has roughly half the caffeine of standard arabica, almost no bitterness at all, a sweeter cup, but also very watery extraction levels (it’s marketed as “delicate). There’s incredibly tiny amounts of this coffee actually produced, so I suspect it will go the way of Kopi Luwak, in that for every 10kg of Arabica Laurina sold, only 1kg of it is real. I’d stay away.

Decaffeination processes are getting better all the time. One of the best decaf coffees I’ve ever had is from Madcap, and it used a sugarcane decaffeination process (that I still don’t understand).

Or you could use my trick: one I use every day. I have an Americano instead of brewed coffee. It usually has about half the caffeine amount (ml for ml) and tastes way better. Brew a double shot of espresso (60ml), which has about 125mg of caffeine (I’ll saved the detailed explanation for another blog pst), and add it to 120ml of hot water. That 180ml cup of “coffee” has 125mg of caffeine. A 180ml cup of pour over or auto drip coffee will have nearly double that amount, around 220-240mg.


Mark has certified as a Canadian, USA, and World Barista Championship Judge in both sensory and technical fields, as well as working as an instructor in coffee and espresso training. He started CoffeeGeek in 2001.

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