Photo by Stirling Noyes/Flickr CC
At lunch last weekend I overheard someone at another table say that when she wanted a greater caffeine buzz, she chose a different roast. I can't remember whether she chose darker or lighter roast for the greater buzz, but it doesn't matter; both answers were wrong. The effect of coffee roasting on caffeine content is so negligible as to be immeasurable except under tightly controlled laboratory conditions.
We generally estimate caffeine content to average 1% for coffea Arabica and 2% for Robusta (coffea Canephora) by weight. The real issue is the caffeine content of the cultivar, i.e. the species (Arabica or Robusta) and especially the variety of the coffee within the species. [Curator's note: As Jerry helped teach me for my book, good coffee -- everything Peet's and also Starbucks sells -- is Arabica.]
The word "varietal" is often incorrectly used referring to coffee. "Variety" or "varietal" is an important word to an American wine producer since our tradition is to label wines by varietal, eg. Zinfandel. In France or Italy, the tradition is to label by the appellation where the wine is grown, and most wines are blends. But generally only coffee professionals encounter the variety of coffee; the consumer rarely knows whether she is drinking Catuai (red or yellow), Caturra, Typica, Mundo Novo, SL28, or Kent, to pick six of the more than 3000 named Arabica varieties. [Curator's note: For single origin coffees, what customers see is a name derived from the country of origin like Guatemala Antigua or a specific farm like Guatemala San Sebastian; for blends you'll see a proprietary name, like Peet's Major Dickason's Blend.]
Back to caffeine. In a couple of studies testing 90 different Arabica cultivars, the caffeine content varied between 0.42 and 2.9%. My morning cup would then vary between 84 and 580 milligrams, depending on which of these varieties was in my cup.
If your morning cup came from a commercial roaster who included Robusta in the blend, we have another level of complexity. Caffeine content in these coffees, in one study, varied between 1.16 and 4.0%. A straight 12 oz. cup, using 20 grams of the 4% coffee, probably wouldn't taste very good, but would definitely provide more buzz: 800 milligrams of caffeine.
As with most things, the more one learns, the more complex a topic becomes and, in a sense, the less one knows. To attempt accurate generalization:
• Arabica averages about half the caffeine as Robusta.
• The cultivar determines the caffeine content.
• Degree of roast has no meaningful effect on caffeine.
• An espresso made from 100% Arabica, on average, has about 70 milligrams of caffeine per shot; a 12 oz. cup of drip coffee made my way in a press pot, using two scoops of coffee per 12-ounce cup -- would have 200 milligrams.
Beware of taking this information very far, because individual responses to caffeine differ widely. Caffeine is metabolized faster by men and slowest by pregnant women. Body weight and eating will affect caffeine absorption.
And don't go running to your coffee store asking which variety a given coffee is. Coffee buyers are concerned with taste, which they want to reflect the origin. While different cultivars grown in the same soil do taste different, it's a bit beside the point of the flavor of the origin (terroir, if you like). We want the taste of our single origin coffees to reflect where they were grown.
No doubt many have used caffeine for stimulation (Balzac wrote an ode to the effects of his 40 cups per day.) I can't say that I have never used coffee as an energizer, but at Peet's we don't think of ourselves as part of a caffeine delivery system. We're part of the pleasure delivery system. When you sip your coffee, think of how good it tastes.