Can you explain why the amount of caffeine in a beverage varies so much between retailers, among types of beverage, and even cup to cup? Everyone seems to ask for the strongest coffee we have, but I don’t know what to recommend. Should I worry about over-caffeinating anyone?
Drowsy in Delaware
Good question! This topic is a complex one because, as it turns out, depending on the coffee and brewing method the amount of caffeine in a coffee beverage can vary greatly!
First, let’s all remember that coffee is the seed of a plant, and therefore has natural variation due to its genetics and environment. This means that there will be differences between and within coffee species and cultivars. It is likely that the expression of genes related to caffeine production are impacted by both biotic (pests) and abiotic (environmental) factors (Mazzafera and Silvarolla 2010). In fact, if you tested all the beans in a bag of green coffee you might find a different amount of caffeine in each bean. A study conducted in Brazil reported a large seed-to-seed variation within coffee cultivars. For example, in the Mundo Novo cultivar, the researchers found a mean value of 10.8 mg/g. However, the range for levels in individual beans was between 5.01 and 20.00 mg/g (Mazzafera and Silvarolla 2010). In a study of 42 C. arabica genotypes from Ethiopia, the caffeine content ranged from 9.1 to 13.2 mg/g (Dessalegn and others 2008). Additionally, there is evidence that individual coffee plants are capable of varying the caffeine content in their seeds from year to year (Mazzafera and Carvalho 1991). Since caffeine is a plant alkaloid, and evolved as a defense compound, it is only natural that species and varieties from different regions with different stressors were able to adopt varying defense strategies. Perhaps you are getting the picture that quantifying exactly how much caffeine in the coffee you serve each day would be a difficult task!
What about roasted coffee? We should briefly consider that, contrary to popular opinion, dark-roasted coffee does not contain more caffeine than lighter-roasted coffee. This misconception probably comes from the fact that darker-roasted coffees have a lighter bulk density due to expansion during roasting. This means, if you are weighing out a dose for an espresso or brewed coffee, you will actually have more coffee and therefore more caffeine in the cup. This is one big reason why we see reports in the popular press of certain companies having higher caffeine contents in their beverages than others. It is all in the dose! One study found a caffeine-content variance of 5.18 to 12.21 mg/g in roasted retail coffee seeds (Hackett and others 2008). If we aren’t worrying about the inevitable variation between beans, it is generally accepted that raw and roasted C. arabica consists of between 0.8-1.4% caffeine and C. canephora from about 1.7-4% (Belitz and others 2004). Others report an average of 1.2% for arabica and 2.2% for robusta coffees (Illy and Viani 2005).
Of course, your real question was about the coffee beverages we drink! Depending on strength, dose, grind, and brewing method, caffeine in coffee can vary from 58 mg/serving to as high as 564 mg in a 16 oz. cup (McCusker and others 2003). It is believed that caffeine is extracted fairly quickly during brewing, and most methods likely extract much of the caffeine present in beans; but it will depend to some degree on your water temperature, turbulence, grind, and contact time (Bell and others 1996; Spiro and Selwood 1984; Spiro and others 1989). For example, espresso preparation extracts between 75-85% of total caffeine, perhaps due to contact time (Petracco 1989). Of course, serving sizes can vary greatly, from 1 oz for a short espresso beverage up to 16-32 oz. serving sizes for brewed coffee. One study found a shot of espresso could vary between 58 and 185 mg/serving, depending on whether it was a single or double shot (McCusker et al. 2003). Another study found an average caffeine content of 107 mg/serving, likely combining single and double shots (Desbrow and others 2012). In fact, a drip coffee was found to contain as much or more caffeine than a double shot of espresso, between 143-564 mg/serving (McCusker et al. 2003). So, if you are looking for a particularly strong pick-me-up, perhaps try a high dose of dark-roast coffee, drip brewed. Or, just chew on some coffee beans!
The fact is, there is no evidence that coffee drinkers have suffered from overcaffeination in any clinical sense. You do not need to worry about your customers overcaffeinating! Important to note is the fact that coffee has been enjoyed for hundreds, if not thousands, of years on a daily basis. A high level of coffee consumption is not accompanied by indicators of toxicity, as demonstrated anecdotally by Nordic cultures that drink lots (up to 14 cups per day) of strong coffee each day. Based on the current scientific knowledge on the topic, it does not appear that caffeine from coffee has any particular risks other than the occasional jitters and sleep disturbances. So, my under-caffeinated friend Drowsy, feel free to promote your delicious product. Coffee is made up of hundreds and perhaps thousands of chemical components and caffeine is just one of them. Embrace your specialty coffee beverage for the unique experience it was meant to be, and by all means, caffeinate!
Emma Bladyka is SCAA coffee science manager. Before moving into the coffee industry, she completed degrees in ecology and botany, and dabbled in the wine industry. She enjoys learning all there is to know about the science of coffee (and more importantly, sharing it with you).
Belitz H-D, Grosch W & Schieberle P. 2004. Food Chemistry. 3rd revised ed. Germany: Springer.
Bell LN, Wetzel CR & Grand AN. 1996. Caffeine content in coffee as influenced by grinding and brewing techniques. Food Research International 29(8):785-789.
Desbrow B, Henry M & Scheelings P. 2012. An examination of consumer exposure to caffeine from commercial coffee and coffee-flavoured milk. Journal of Food Composition and Analysis 28(2):114-118.
Dessalegn Y, Labuschagne MT, Osthoff G & Herselman L. 2008. Genetic diversity and correlation of bean caffeine content with cup quality and green bean physical characteristics in coffee (Coffea arabica L.). Journal of the Science of Food and Agriculture 88(10):1726-1730.
Hackett J, Telepchak MJ & Coyer MJ. 2008. Analysis of Total Caffeine and Other Xanthines in Specialty Coffees Using Mixed Mode Solid-Phase Extraction and Liquid Chromatography-Diode-Array Detection After Microwave Digestion. Journal of Analytical Toxicology 32(8):695-701.
Illy A & Viani R. 2005. Espresso Coffee: The Science of Qualtiy, 2nd ed. San Diego: Elsvier Academic Press.
Mazzafera P & Carvalho A. 1991. Breeding for low seed caffeine content of coffee (Coffea L.) by interspecific hybridization. Euphytica 59(1):55-60.
Mazzafera P & Silvarolla MB. 2010. Caffeine content variation in single green Arabica coffee seeds. Seed Science Research 20(03):163-167.
McCusker RR, Goldberger BA & Cone EJ. 2003. TECHNICAL NOTE: Caffeine Content of Specialty Coffees. Journal of Analytical Toxicology 27(7):Petracco M. 1989. Physio-chemical and structural characterisation of espresso coffee brew. Proc. 13th ASIC Coll. Paipa. p. 246-261.
Spiro M & Selwood RM. 1984. The kinetics and mechanism of caffeine infusion from coffee: The effect of particle size. Journal of the Science of Food and Agriculture 35(8):915-924.
Spiro M, Toumi R & Kandiah M. 1989. The kinetics and mechanism of caffeine infusion from coffee: The hindrance factor in intra-bean diffusion. Journal of the Science of Food and Agriculture 46(3):349-356.