How Much Caffeine is in My Coffee?
Ahh, caffeine. While in our last blog we celebrated the ability to enjoy the taste and experience of a great cup of coffee without the caffeine, today it's all about the stimulants.
Many different variables go into the final amount of caffeine in a given cup of coffee. Caffeine content can change for a variety of reasons including bean variety and brew method. How does that happen?
Bean size: Pretty straightforward. Larger beans mean more of everything, including measurable caffeine per bean. This can even vary among beans harvested from the same plant. Weighing instead of measuring by volume during the brewing step helps avoid the effect that differences in bean size or density can have on the final extraction.
Species of bean: Robusta beans have up to twice as much caffeine as Arabica beans. Robusta can even be added to instant coffee mixes or high-volume commercial blends to be marketed as higher-caffeine. This is why truck stop coffee often packs such a punch. Sometimes Specialty coffee roasters will use a modest proportion of Robusta in espresso blends in order to improve crema characteristics. While many roasters get good results with this approach, we have found that a careful blend of Arabica coffees produces exceptional crema while avoiding the oddly medicinal and rubbery character some Robusta varieties can impart.
Darkness of roast: This question seems to come up frequently. Which roast has more caffeine, light or dark? The answer is neither... and both. The reasoning is a little tricky but here's a brief rundown: Caffeine is stable throughout all stages of roasting, be it light, medium or dark. That means when a pound of green coffee is roasted, it will contain the same measurable amount of caffeine when it is done roasting regardless of the roast level. What is lost are volatile compounds, especially water. So that one pound of green coffee might weigh 0.85 pounds as a light roast, 0.82 as medium and 0.80 as a dark roast.
At the same time, the darker the roast, the more the beans will physically expand and thus occupy more volume. The result is if you measure your dark roasted coffee by weight, the resulting brewed coffee will have a slightly higher caffeine content than a cup brewed from a lighter roasted bean. If however you measure the same coffee by volume, the result is reversed. The light roasted beans expanded less during the roasting process, so more beans will fit into a given measured volume. This gives the light roast more caffeine. At Night Owl Roasters, we measure by weight to keep each cup consistent.
Grind size, brewing method, water temperature, and duration of brew: These are all sort of interrelated, so they get lumped together. Finer grinds have more surface area and greater extraction potential for caffeine. A lungo espresso shot will generally have more caffeine than a ristretto because you have passed more water through the grounds for a longer time. While the French press uses a very coarse grind, the longer the coffee is steeped before plunging the more caffeinated it will be. We advise adjusting your extraction time to optimize your extraction based on flavor, rather than trying to control the caffeine levels.
Caffeine is over 40 times more soluble in 200 degree water than in room temperature water. Cold brew would in theory have less caffeine than an equivalent hot brew method because caffeine is far less soluble at lower temperatures. But cold brew has extremely long extraction times – on the order of 18-24 hours. The extraction time of cold brew is therefore over 350 times as long as standard drip coffee. Our experience is cold brew coffee has little or no reduction in caffeine level.
Serving size: A shot of espresso has less caffeine per serving, 80 mg compared to a 12 oz cup of drip coffee, which can have upwards of 220mg. Per ounce, however, it has significantly more. This is why we drink small shots of espresso, and 12 to 16 or more ounces of brewed coffee.
As you can see, a lot of things go into how much caffeine actually ends up in your cup. If all this hurts your brain as much as it does ours, here is some advice: Drink the coffee you enjoy most, in whatever quantity that satisfies. Know the caffeine is there and be happy. People don’t pick their favorite wine because it has an alcohol level of 13.0 percent versus 12.7 percent (right?). It is selected based on its quality and flavor. Treat your cup of coffee the same way.
Remember, if you have any coffee-related questions, ask them in the comments or by email to media(at)nightowlroasters.com. We'll try to answer them in the next blog!