A bit cryptic I agree and the question should rather be how much caffeine do you think you have in your cup of coffee? But since you have no way of measuring that, unless you have access to a chemical laboratory, you can only control the amount of coffee beans you use for your cup of coffee and the brewing method. And you can use those measures as a proxy for the amount of caffeine you consume.
Why worry about the amount of caffeine?
Because the European Food Safety Authority (EFSA) has just published an opinion on caffeine and alertness. This new opinion confirmed that at least 75 mg of caffeine is necessary to improve alertness. For some reason SmithKline Beecham Limited wished EFSA to agree that 40 mg of caffeine would have the same effect. But EFSA didn’t budge. EFSA was clear in saying that
“at the particular dose range between 40 and < 75 mg, no effect of caffeine was found on the majority of outcome measures of reaction time“
after reviewing a number of studies submitted by the applicant.
The EFSA scientists also believed that
“increased alertness might be a beneficial physiological effect”
and I assume we all take that for a given. So there you have it, your cup of coffee needs to contain at least 75 mg of caffeine to wake you up.
How to get enough caffeine in your cup of coffee?
As a rule of thumb it’s usually presumed that a regular cup of coffee contains 100 mg of caffeine but it may range between 40 and 176 mg and to be honest the mean is probably closer to 80 mg. This will fit with the standard recipe when calculating exposure of 7 g of ground coffee beans for a cup, which would result in close to 80 mg of caffeine in the cup since arabica coffee beans contain about 11 mg/g. So far so good and we would be over the magical 75 mg caffeine alertness level.
But remember that we haven’t yet looked at the volume of coffee in the cup. The size of a cup can vary from as little as 25 mL (Greek coffee) to a large cup of 330 mL and in extreme cases up to 480 mL for a Starbucks Pike Place cup or a McDonald’s Mocha Frappe. The volume of coffee in an average cup in Europe is actually 120 mL, while in the USA it would be closer to 240 mL.
So how does the volume of coffee influence the caffeine level? As it happens not that much since we seem to keep the caffeine level fairly constant for a cup irrespective of size. An Italian espresso of 30 mL would still contain a minimum of 40 mg of caffeine and could be close to the 75 mg mark. This is strong coffee but might be a little low in caffeine to reach the EFSA benchmark. On the other end of the spectrum is a typical 240 mL American cup of coffee that might not hold more than 95 mg of caffeine. Not so strong I would say, no offence intended, but well over the desired level if you drink it all. Even the large McDonald’s Mocha Frappe of 480 mL limits the caffeine to 125 mg per cup, but Starbucks Pike Place is not so restrictive offering 330 mg of caffeine per 480 mL cup.
Well I have to confuse you even more because tastes are different and brewing methods abound. If you go for robusta coffee and use the same amount of beans as for arabica you would double your caffeine intake.
You might think that a strong, rich flavour would indicate an extra dose of caffeine, but the truth is that light roasts actually pack more of a jolt than dark roasts. The process of roasting burns off some caffeine.
And finally, while the caffeine concentration in a normal brew of filtered coffee would amount to 0.6-0.8 mg/mL, it would be 1.7-2.3 mg/mL in the coffee expressed from an espresso coffee machine. But you would obviously pick the size of your coffee cup accordingly to not overindulge.
All I can say is that if you feel alert you have probably exceed the 75 mg of caffeine required to improve your reaction times. Good on you, you will get through the day at your peak.