Which coffee brewing method has the most caffeine? Drip brew? French press? Espresso? Many believe the answer is espresso. After all, shots of espresso are what we see people order when they are sleep deprived or up against a deadline. Espresso is concentrated coffee, brewed by the pressure of hot water quickly flowing through finely-ground coffee beans. With espresso being a small, concentrated amount of coffee, it would make sense that it has the most caffeine. But, drip brew coffee has hot water continuously passing through coffee grounds for a longer period of time, potentially extracting more of the caffeine out of the bean, so drip brew has to have more caffeine than espresso. Then again, with a French press, coffee is fully immersed with hot water for a full infusion, steeping with full on contact for 4 minutes, so a French press has to extract more caffeine than espresso and drip brew. Right?
Length of brew time
Not only do dark roasts generally have less caffeine than light roasts, but espresso also has a lower caffeine content than drip brew! The reason is the length of time that the coffee beans are in contact with water for extraction. With drip brew, hot water is continuously dripping through a bed of coffee grounds for 3-4 minutes. A shot of espresso is pulled in 20-30 seconds. Compared to drip brew, where coffee is in contact with hot water 6 times longer than the hot water that is in contact with coffee grounds during an espresso extraction, you can see how drip brew coffee would have more caffeine. It’s easy to see that, in terms of length of brew, drip brew coffee makes contact with hot water much longer than espresso does.
Back in ’79, while I was still running around in diapers, Bunker and McWilliams were busy publishing a paper with their research findings on the caffeine content of common beverages. Here are their coffee-based findings (caffeine content noted in mg):
-Espresso: 1 cup (1.5–2 oz, 45–60 ml) = 100 mg
-French press: 1 cup (7 oz, 207 ml) = 80–135 mg (107.5 mg average)
-Drip brew: 1 cup (7 oz, 207 ml) = 115–175 mg (145 mg average)
Case closed. Drip brew has the highest caffeine content and espresso the lowest. Well, in reality, it’s not that straight forward and is a little difficult to gauge. You may have noticed that Bunker and McWilliams measured caffeine content based on serving sizes that are normally consumed. You can see that for French press and drip brew, they measured based on a 7 oz cup but espresso was based on a 1.5-2 oz cup. This makes sense (who would drink 7 oz of espresso?) but shows that they weren’t really measuring apples to apples. I also believe the measurement of caffeine content depends on a lot of other factors as well.
Remember that coffee used for espresso is dark-roasted, so by default the beans being used are already lower in caffeine content. The amount of coffee grounds used can also vary by person based on preference. Some may use more beans than others so the resulting cup will have a higher caffeine content than another cup, brewed by someone else, using fewer coffee beans. Also, if French press coffee steeps for 4 minutes, usually a minute longer than drip brew, why doesn’t French press coffee have the highest caffeine content? The answer is the coarseness of the coffee grounds. The size of the grind makes a difference. For French press coffee, we use a coarse grind. For drip, a medium grind. Espresso, a fine grind. If you have a conical burr grinder, you may notice that you have to “dial in” the right grind to get your coffee to taste better. Maybe it’s too coarse, so you adjust the setting. Or it’s too bitter, so you adjust the setting. Depending on the size of your grind, the amount of time it takes to brew should be adjusted. If you leave all other variables the same (amount of coffee used, amount of hot water, brew length, etc.), a finer grind can mean more caffeine extraction. As we saw with the research by Bunker and McWilliams, beverage size also matters. If we look at caffeine content per ounce, espresso would win. Just a thought.
One last thought on caffeine. If you normally drink coffee in the morning to help you wake up, you may want to experiment with when you drink that first cup. Neuroscientist Steven Miller has done research on chronopharmacology. (Don’t feel bad, even my spellchecker didn’t know what the heck this was and let me know with a long, red squiggly.) Chronopharmacology is a branch of chronobiology concerned with the interaction of biological rhythms and drug action. If you’ve ever drank a cup of coffee to wake up and felt like it just didn’t do much for you, it might have to do with when you drank it. Our bodies release the hormone cortisol at certain times of the day. Cortisol generally spikes between 8:00 – 9:00 AM, 12:00 – 1:00 PM and 5:30 – 6:30 PM. During these times, we naturally become alert due to the increased cortisol in our bloodstream. Part of pharmacology is administering drugs at the right time for maximum effectiveness and to avoid creating tolerances. If you’re looking to coffee for helping you with being alert, Miller suggests drinking your coffee between spikes and recommends drinking between 9:30 – 11:30 AM.
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