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According to the USDA, the caffeine content in 100 gram of brewed coffee is about 40 milligram.

According to the USDA, 100 ‎gram of restaurant-prepared espresso contains 212 milligram of caffeine. That means one gram of espresso contains about 2.12 ‎milligram of caffeine.‎

According to coffee.org, a single coffee bean contains 1.9 milligram of caffeine on average, which translates to 1.2-1.5 gram caffeine per 100 gram of beans.

It seems these numbers don't match up. Why is that?

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    I copyedited your question a bit but I'm not sure what your numbers refer to. Specifically, where did you get the 212 milligram of caffeine per 100 gram of coffee? Are you referring to brewed coffee or whole beans? Please edit your question to include a reference, because it's not entirely clear. For example, here they talk about 80mg of caffeine per 10 gram of beans.
    – JJJ
    Sep 26 at 1:01
  • Through my reading of various Italian and English article , they wrote that the basic is : every 100 grams of Arabica ground coffee contains 212 milligrams of caffeine, and they mention the organization and its name is the USDA , which she also mentioned . According to this fixed rule , we can say that each gram of Arabica coffee contains 2 , 12 milligrams of caffeine , is this calculation correct ? I am waiting for an evaluation of my words . Thanks Sep 26 at 17:51
  • Can you provide a link to the article mentioning that 212 mg figure? I'm not disputing it but it's important that everyone is working from the same figures. For example, at first I though you meant 100 grams of brewed coffee rather than 100 gram of grounds.
    – JJJ
    Sep 26 at 17:59
  • on this site: coffee.org/pages/…, says that (On average, a single arabica coffee bean contains 1.9 milligrams of caffeine (1.2 - 1.5g of caffeine per 100g).). tell me what it means Sep 26 at 18:37
  • That's very different from the 212mg you mentioned earlier right? 1.2g is 1200mg per 100 gram of coffee beans. So if you brew an espresso using 8 gram of grounds then the grounds used for that have 1200/100*8=96mg of caffeine in them. If about half of that gets into your espresso (and the other half stays in the puck) then you have 40mg of caffeine in your cup.
    – JJJ
    Sep 26 at 18:42
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There are a number of things to consider regarding these numbers.

From a coffee perspective, it's important to note the difference between caffeine in the bean and caffeine in the coffee drink brewed from those beans. When you extract liquid coffee from grounds you extract some, but not all elements. Caffeine extraction, for example differs based on the brew method.

As the USDA links in the question show, 100g of espresso contains 212mg of caffeine while 100g of brewed coffee contains only 40mg of caffeine. That is because espresso is brewed under pressure, which allows more elements to be extracted from the coffee bean using less water.

On the other hand, to make 100g of espresso you would use much more coffee grounds than you would when brewing 100g of brewed coffee. You might be brewing espresso with a brew ratio of 1:2 (15g of grounds to get 30g of liquid espresso) while 1:16 is a good ratio for filter coffee. In that sense, espresso is just more concentrated, with respect to caffeine but it goes for other solubles (particles in the coffee bean which you extract into the coffee liquid) too.

It should also be said that coffee isn't an exact science. Caffeine content can vary slightly per bean (that's why coffee.org lists the average figures). And another variable that may affect caffeine extraction is the brewing process. Just like different brew parameters (temperature, grind size, pressure, etc.) can affect espresso flavor, they might also affect caffeine extraction. I'm not claiming that any of these brew parameters affect caffeine extraction specifically, but they might.

From a language perspective, there might be some confusion about the description on coffee.org. They describe caffeine content in the average arabica bean as well as the content per 100g of beans. One bean weighs less than one gram, so it might cause confusion. They provide the following figures:

  • 1.9mg of caffeine per bean
  • 1.2-1.5g of caffeine per 100g of beans

Taking the average of 1.35g of caffeine per 100g of beans, we find there are about 1.35*1000/1.9 = 710 beans in 100 gram of beans.

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  • good Nathan, these USDA links that I read in retirement planning and that I looked for but could not find it, now this information is very useful and correct they answered my questions, thanks. Sep 27 at 8:42
  • There is also the matter of brew to drink ratio. For example, a drip coffee drink is composed almost entirely of brewed coffee with maybe some milk or sugar added, while an espresso drink is composed only about 20% or less of brewed espresso. This has a significant impact on the amount of caffeine you end up consuming by drinking a single coffee-based drink.
    – R Mac
    Oct 7 at 16:16

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