Coffee Research Figures -- For the Curious (and Son Ton)

After I posted earlier about the University of Glasgow study published in Food and Function Magazine (you can read the study for free here, but you need to register for an account to read the full thing), Son Ton commented about standardization of sizes. I actually had read the study, and meant to mention the methodology used. I was rushed and hadn't had my coffee yet so it slipped my mind {C}and I posted without it. Rather than updating the old post, I decided to post the figures and more info in a separate post in case Son Ton wants to comment on it now that there's more information. Here's a table taken from the info provided in the study. According to the exposition, the researchers bought a "single shot" at each coffee shop, and measured them in milliliters before preparing them for the caffeine test. 

Shop serving/ml caff/mg
Pattiserie Francoise 52 322
University Cafe 49 260
Cafe Cinnamon 59 242
Paperino’s 50 205
S’mug 32 173
Costa Coffee 25 157
Heart Buchanan 24 156
Jellyhill 63 151
Baguette Express 45 140
Chapter1 26 140
Peckham’ 70 140
Little Italy 23 129
Coffee @ 291 49 98
Crepe a Croissant 34 95
Kember & Jones 43 90
Beanscene 48 77
Tinderbox 25 75
Morton’s 35 73
Antipasti 36 72
Starbucks 27 51

As you can see from the table, the shots did indeed vary in volume from 23 ml to 70 ml, but the correlation between volume and amount of caffeine is far from 1:1. In fact, there are three shots that measured 140mg of caffeine; one of them measured 26 ml in volume, one measured 70 ml and one measured 45 ml. The researchers didn't offer any information on the dosing, which, I suspect, would probably have a clearer correlation to the amount of caffeine. Even then, though, water temperature, time and pressure would certainly affect the amount of caffeine extracted -- and that doesn't even take into account the difference that varietal, bean origin and roast would make.

As a matter of curiosity, I'd be interested in knowing those things and seeing how the correlations work out, but I still think the caution given by the researchers is warranted. While there's definitely a core of espresso drinkers who'd consider those things, most casual drinkers probably aren't going to analyze that deeply. If anything, most are likely to assume that a "bigger" espresso has more caffeine -- and as the chart makes clear, that's definitely not the case. I guess the biggest takeaway is that, if you're among the caffeine-sensitive, you can't rely on the "official" word about how much caffeine is in your shot of espresso.

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