Caffeine can either be friend or foe. The content of caffeine in coffee is polarizing to consumers, debated by professionals, and publicized in the media. Unfortunately, many of the stories we read or hear about do not provide adequate or enough detailed information to present all the facts about caffeine to the general public.
Recent media topics include comparing drip coffee to espresso, and presenting how much caffeine is in each cup of coffee. A few online searches for coffee caffeine content information yielded vastly different data from each source. Caffeine confusion is created by reports that lack specific details, reports that contradict each other, and do not include the answers professionals and consumers require.
Caffeine (C8H10N402) is a white, crystalline, odorless and bitter tasting solid. Caffeine naturally exists in coffee plants and acts as a natural deterrent for pests.
Caffeine is most commonly measured as a weight/weight percentage. Arabica coffee contains about 1.2% caffeine while Robusta coffee contains about 2.2% caffeine (coffeechemistry.com). However, coffees from different origins have different caffeine levels due to variations in growing environments and plant genetics. For example: Tanzania Peaberry 1.42%, Yemen Mocha Mattari 1.01%, Guatemala 1.20%, Kona 1.32%, Zimbabwe 1.1% and Ethiopia Harrar 1.13% (coffee.org).
Contrary to popular reporting, scientific research concludes that caffeine is not cooked away during roasting. During roasting, coffee loses between 15% and 20% weight. “Caffeine melts at 235-237.5°C (455-459.5°F) and sublimes without decomposition at 176°C (352.4°F)” (Coffee Technology, Sivitz, 1979). For the majority of the roast profile, the temperature is below the melting point of caffeine and the internal temperature of the bean does not have enough time to reach a level that would allow the sublimation process to affect the coffee’s caffeine content. (“The Mahor Systematic Error Sublimation of Caffeine.” UKessays.com. 11 2013)
When researching caffeine in beverages it is critically important to detail the unit of measurement and to identify the variables used in preparation. When consumers brew coffee beverages the dosage is listed by volume (tablespoons), while specialty coffee professionals measure coffee dosage by weight (grams or ounces). This difference may seem insignificant; however, because of variations in density, it will have a considerable impact on the caffeine in the beverage.
Coffee Analysts measured the difference between weight and volume to illustrate this point. Green Arabica coffee weighed 18.5 grams per 100 beans, with a density of 0.69 g/mL using the free-flow bulk density method. A light-roasted 100% Arabica national brand weighed 13.5 grams per 100 beans with a density of 0.36 g/mL, and dark roasted 100% Arabica national brand weighted 12.35 grams per 100 beans with a density of 0.28 g/mL.
As you can see from the limited weight and density data above, dark roasted coffee is significantly less dense. When measured at the same volume, dark roasted coffee will weigh less, producing less caffeine in the beverage, assuming all other brewing parameters are constant.
The dynamics of brewing that affect extraction rates and beverage brew solids also affect the amount of caffeine transferred from the beans to the brew. A heavier dosage of coffee will result in greater caffeine in the beverage. A finer grind will allow the extraction of caffeine more efficiently. Hot water allows caffeine to extract more easily. The size and shape of the brew basket along with the length of the brewing cycle will affect how much caffeine is passed from the grinds to the beverage. Using Robusta as a component in a coffee blend will increase the amount of caffeine in the beverage as well.
In the instance of Huffington Post’s recent article, “How Much Caffeine Is Actually in Your Coffee, From Dunkin’ to Starbucks” (http://www.huffingtonpost.com/thrillist/caffeine-in-coffee_b_3671665.html) the most logical explanation for the variations in caffeine content in your beverage is marked by differences in the brewing recipe. The expected variations for foodservice preparations are dosage and grind particle size. For at-home preparations, dosage, particle size and water temperature are the prevalent variations. Comparing caffeine in prepared beverages is different than comparing the inherent caffeine content of green coffee or roasted coffee beans because of the variables in extraction during the brewing process.
When comparing espresso to drip, the caffeine conversation becomes more convoluted. Consumers and professionals often experience caffeine confusion when the beverage size and unit of measurement isn’t clearly stated. For clarity, caffeine content is best presented as milligrams per fluid ounce (mg/fl oz.). CaffeineInformer.com presents many different coffee products in its database using the appropriate format, however, information regarding the brewing variables and coffee species used is unknown. Caffeine in espresso is listed at 77 mg and brewed coffee is listed at 163 mg in the beverage. Since the beverages’ sizes are not comparable, caffeine confusion begins. A more appropriate comparison is caffeine measured per fluid ounce. Caffeine in espresso is listed at 51.3 mg/fl oz. and brewed coffee is listed at 20.4 mg/fl oz. One ounce of espresso has significantly more caffeine than one ounce of drip coffee, which can be attributed to reduced particle size and increased coffee dosage during the brew process.
In the case of cold brew, Mike Strumpf presented excellent data in “Keep your Cool with Cold Brew” published by the SCAA. Cold brew coffee has higher levels of caffeine per fluid ounce in beverages because of a heavier coffee-to-water ratio and substantially longer brewing time.
In Latin, it is said “sola dosis facit venenum” meaning the dose makes the poison. When discussing caffeine, we must first consider the dose: specifically, the beverage size and how the beverage was prepared.
By Spencer Turer, Coffee Analysts
Spencer Turer is vice president of Coffee Analysts in Burlington, Vermont. He can be reached at email@example.com.