The truth behind caffeine in light and dark roasts...
I am sure that many of you have heard that dark roasted coffee contains more caffeine than light roasted coffee, and yet I am sure you may have also heard that light roasted coffee contains more caffeine than dark. Which is it?
Light roast coffee and dark roast coffee contain relatively the same amount of caffeine. Where the confusion comes in is how you measure your beans.
To understand the caffeine content in our beans we have to understand the roasting process as well. When beans are put into a roaster they are introduced to heat which starts to remove the remaining water content in the beans. During the roasting process there are different stages which help the roaster understand how far the bean has gone on the scale of light to dark. As the water is removed from the bean the structure begins to change and it will go through what's called first crack where the bean will almost double in size and has released a good portion of its water content and energy. If the roaster stops the roast here it will be on the light side. If the roaster decides to continue, the bean will expel any remaining liquid it has until it goes through its final phase which is called second crack. This is where the bean in essentially maxed out and the roaster has to be careful not to burn the batch but also achieve the perfect dark roasted bean they were looking for.
Well what about the caffeine then?
As we learned in the roasting process the beans that were stopped at an earlier stage still has some water content to them which in turn means they weigh a little more. They are more dense vs their dark roasted counterpart which has very little water content left and is relatively lighter or less dense than the light roasted coffee. So this is where measuring your coffee is so important. If you just use a scoop to measure your coffee, your scoop of light roasted coffee is going to have more beans than the same scoop of dark roasted coffee. This is where the belief that light roast coffee has more caffeine because if you brewed each of those scoops separately you have more beans in the light roast which would skew our caffeine. This is incorrect because the beans still have the same amount of caffeine, you are essentially just making one stronger than the other.
If you brew your coffee by measuring weight we will find that the opposite is true. If you measure out 1 oz of light roast beans and 1 oz of dark roast beans you will have more dark roast beans than light roast beans. This is where some people might say that the dark roast contains more caffeine, but again, you are just making one stronger than the other by using more beans.
So the conclusion is - coffee contains the same amount of caffeine regardless of light or dark roast. Caffeine doesn't start to break down in the roasting process until around 450 degrees which typically if you make it to that temperature you won't even have a palatable coffee anyways.
Choose your coffee by taste preference and brew it how it tastes best to you. My recommendation and experience has lead me to using weight measurements for all of my brews. I feel that I have so much more control over my flavor profile because I can systematically tweak my brew and then be able to duplicate it with relatively little effort. For example, I use 1 oz of grounds (light or dark) to every 16 oz of water. This is easy to scale as well...0.5 oz grounds / 8 oz water, etc... If that brew is coming in too strong, scale it back a few grams, and vise versa. Then you can say with this coffee I like 0.9 oz of grounds to 16 oz of water, and with this coffee I like 1.1 oz of grounds to 16 oz of water. This way allows you to be more precise whereas eyeballing it may or may not work. This is also coffee we are talking about, so lets not screw around!