Did you ever wonder how much caffeine can be found in a cup of coffee? Unsurprisingly, this depends on many factors. So does the coffee species play a role, the climate in which the coffee has been growing and harvested, the method of brewing but also the amount of coffee per cup influence the total caffeine content. Here we will go over the different topics and tell you how to brew the strongest coffee.
We already touched partly on this topic in another blog “Ecology of a good coffee”. A coffee plant is, like all plants, dependent on natural conditions. Optimal conditions will cause a coffee plant to flourish whereas with less optimal conditions a coffee plant might be struggling to survive. What has the survival of a coffee plant to do with the beans? Coffee plants might not only give less seeds when the conditions are not optimal, they can also change the contents of the seed (beans). This difference is more pronounced than you would think and caffeine content varies slightly on a year to year base, dependent on the weather of that year.
There are over 120 different species within the genus Coffea (See Coffee species for a list of all species). Although all those coffee plant species give rise to coffee beans, the taste and caffeine content of those beans are different. Here we will pick out three species and look at their caffeine content: Coffea Arabica (Arabian coffee), Coffea liberica, Coffea canephora (Robusta). To begin with, the most used coffee bean; roughly 60 percent of the world coffee consumption is brewed with the Arabian coffee bean. However, this is not the “strongest” coffee bean in contents of caffeine. The beans of Coffea arabica contain approximately 10 mg of caffeine per gram of dry mass. The Coffea liberica beans do slightly better and have about 12 mg of caffeine per gram of dry mass. Whereas the Robusta coffee beans (Coffea canphora), which is the second most used bean, have double the content of the Arabica bean: 20 mg of caffeine per gram of dry mass. The Robusta bean is also the strongest coffee bean in terms of caffeine.
Often people think that the roast type (Dark, medium of light) plays a role in the ultimate caffeine content as well. E.g. dark roasted coffee beans should be stronger than light roasted coffee beans. We found some numbers of the difference between roasted and unroasted beans and it turns out that caffeine content of Coffea liberica rise from 12 mg to almost 16 mg. However in the Arabica bean the rise in caffeine content is negligible (10 -> 11 mg) (Mubarak, Croft, Bondonno, & Din, 2019). However, here we are talking between the difference of unroasted – roasted beans. Going from a light roast to a medium and dark roast the effect might actually be the opposite. Roasting the beans more will make the beans expand and give a slight loss to the caffeine content. It must be said that this loss is also minimal. So what is the difference? The flavor of a darker roast will shift from the caffeine to a less bitter flavor. This is the reason coffee shops generally like to use dark roasted beans.
Whereas the roast does not influence the caffeine content much, the method of brewing will differentiate caffeine content per cup of coffee. Many variables again influence the ultimate caffeine content. So does the grind size of the bean matter and the temperature of the water influences how much caffeine is extracted. Most important however, is the brewing time. The longer the time water can extract caffeine from the beans the more it will extract. The ultimate variable that influences the caffeine content is of course the cup size. Although an espresso is strong, a larger cup might in total contain more caffeine (See figure below).
As you can see there are too many elements playing a role to give a definite answer to the question: “How much mg caffeine is there in one cup of coffee?”. Nonetheless, taking standard amounts of beans and cup sizes, the following amounts of caffeine are a good indication: