Four out of five Americans drink coffee either daily or on occasion, according to the National Coffee Association of the United States, and the average daily consumption of coffee in America was more than 400 million cups in 2009. Some people drink coffee, at least in part, for its caffeine content, which offers a stimulant effect. A variety of factors affect the caffeine content of coffee, such as bean origin and variety, as well as roasting and brewing methods.
Beans
Every pot of coffee starts with ground coffee beans and there are two main varieties of coffee beans, robusta and arabica. Robusta beans are lower in quality and are often used for instant, prepackaged or pre-ground grocery store brands. Robusta beans are higher in caffeine than arabica beans, but in many cases the beans are blended. Arabica beans are high-quality beans used in gourmet coffeehouses and high-end restaurants. According to Coffee Research, arabica beans account for 75 percent of the world's consumption.
Roasting
While it all starts with the bean, and robusta beans are higher in caffeine content, roasting and brewing methods have a significant impact on the caffeine content of your coffee. It is common misconception that a darker roast is higher in caffeine content. Actually, the opposite is true. Much like alcohol, which evaporates as it is "cooked," caffeine burns away during roasting. This is why longer, darker roasts are lower in total caffeine. The roast with the greatest caffeine punch is a high-quality, light roast arabica that has been properly handled and prepared.
Brewing
Like roasting, brewing is another controllable factor that influences the caffeine content of coffee. Brewing factors include how finely the beans are ground, brewing method and length of brewing time. Using finely ground beans and the drip method of brewing yields the highest caffeine content because the grounds are in contact with water for the longest period, according to Coffee Facts. A 5 oz. cup yields from 115 to 175 mg of caffeine. Percolated coffee yields less caffeine, about 80 to 135 mg per 5 oz. cup. A shot of espresso typically provides 80 to 100 mg of caffeine, while instant coffee provides the least amount of caffeine, averaging 65 mg per 5 oz. cup.
Coffeehouse Brews
According to a review conducted by the Center for Science in the Public Interest, in general, Starbucks' coffees offer the highest caffeine content of the popular coffeehouse chains. Starbucks is followed closely by Einstein Brothers. On average, a 16 oz. Starbucks brewed black coffee provides 320 mg of caffeine. The same size of an Einstein Bros. regular black coffee offers slightly less, at 300 mg. Dunkin' Donuts takes third, with its 16 oz. regular black coffee providing about 206 mg of caffeine.
Considerations
Many factors impact the caffeine content, and of course the larger your cup, or serving size, the more caffeine you will ingest. A 16 oz. cup from a coffee shop is typically nearly three times larger than the mug you might use at home. At the coffeehouse, you can in many cases choose your own bean variety and roasting method. Despite these factors, caffeine variation per 16 oz. cup will rarely exceed 100 mg.
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