There are many misconceptions about the caffeine content of coffee, which is called strength in everyday language. According to common belief, the strongest coffee is espresso made from good- quality coffee (100% Arabica) beans, while the weakest is the American-style "mug" coffee. In general, two or three coffees are recommended a day, but it this really correct? First of all, let's see what caffeine is.
Caffeine is a white, bitter, water-soluble chemical compound (1,3,7-Trimethylxanthine) known for is stimulating effect. When consumed in large quantities – 100 g per day – it can cause death. However, its average daily intake is altogether 400 mg per day.
The two species of coffee – Arabica and Robusta – differ in their caffeine content besides their taste and character. The caffeine content of Arabica coffee is 1.2-1.8%, while Robusta contains approximately twice as much caffeine, about 2.4-2.7%. However, the caffeine content of coffee drinks not only depends on the types of coffee beans used, but also on the methods of preparation. Many people identify the strength of coffee or its high caffeine content with the body of coffee that is the intensity of coffee flavour. In fact, the opposite is true: the "strength" varies according to how fast the brewing method of the given beverage is. The dissolving of caffeine, which is a water-soluble material, takes time. Consequently, the longer the coffee is in contact with hot water, the longer it soaks, the more caffeine gets released from it. Accordingly, the caffeine content of an espresso or a latte made with espresso brewed fast (in about 25-30 seconds) is not more than 30-50 mg per cup. If that drink is made from 100% Arabica coffee, one can have even 8-10 cups a day, as one does not consume more than the average daily dose of caffeine; while in the case of Robusta coffee, one can drink only half of this amount.
In contrast, a coffee drink brewed longer - for example, a filter coffee, an aeropress, or a chemex - from 100% Arabica contains as much as 75-130 mg caffeine per cup, while the same brew made from Robusta coffee can have up to 200 mg caffeine per cup.
As we have seen, the amount of coffee to be consumed cannot be defined simply in terms of the number of cups. It is also important what and how we consume. Most of coffees on the store shelves are blends, and contain significant quantities of Robusta coffee (Tchibo Family 100%, Paloma Douwe Egberts 100%, Lavazza Crema e Gusto 70%). It is therefore recommended indeed that one should drink less of these; for example, only 2 cups of brewed filter coffee a day. Nevertheless, those people who love coffee and want to drink several cups a day not only for its effect but because they enjoy it, should choose high-quality Arabica coffee and drink it in the form of an espresso or latte.
Keep in mind that there are many other sources of caffeine besides coffee, including tea, soft energy drinks, chocolate and certain medications. So take in account these sources too, when calculate the daily dose of caffeine!