Observation: I've been using up the last of a pound of coffee (Rocket Brand from Cupper's) that's right around the 15 day mark. Normally, my coffee doesn't have a chance to age this much, but shipping problems meant I got my coffee about 9 days post roast this time. I use this blend a lot, and really like it for it's balance of chocolate and fruit. I also like it because it usually seems to have less caffeine than the other blend I started with (Godfather from Fratello). With the Rocket Brand, I can have up to 6 double shots a day (even one after supper) with little noticeable effect. With the Godfather blend, it's usually 3 max. before I get serious shakes.

Any time I get the Godfather blend, it's always at least a month post-roast, and so I've stopped buying it from my local coffee shop except in dire emergencies. This time, the Rocket Brand seems to be affecting me a lot more, so I've been treating it like the Godfather blend.

I know that as the coffee ages, you need to grind finer and/or dose higher to get similar results in the cup, otherwise it will blonde faster. Perhaps grinding finer allows us to extract the same amount of some of the more volatile solubles which have diminished over time, but more of the caffeine, which hasn't.

Has anyone else made a similar observation?

Does this make any sense, or does this just sound like an artist trying to think scientifically and doing a poor job?

brokemusician77 wrote:Does this make any sense, or does this just sound like an artist trying to think scientifically and doing a poor job?

The latter.

Oh well. Perhaps there's something to be said for being inquisitive.

I haven't noted this effect, but that won't prevent me from offering a good 'ol thought experiment.

brokemusician77 wrote:I know that as the coffee ages, you need to grind finer and/or dose higher to get similar results in the cup, otherwise it will blonde faster. Perhaps grinding finer allows us to extract the same amount of some of the more volatile solubles which have diminished over time, but more of the caffeine, which hasn't.

Does the brew ratio of espresso made from your older coffee also change (e.g., from double to ristretto range)? Because if the amount of caffeine extracted is determined by water contact time, I would expect the caffeine extracted to decrease as coffee ages since most baristas pull the shots shorter with past-prime coffee.

brokemusician77 wrote:Oh well. Perhaps there's something to be said for being inquisitive.

Absolutely. But here's my reasoning: there's no way for additional caffeine to get into the roasted coffee. To get more caffeine in the cup, you need to a) use more coffee; b) extract at a hotter temperature; or c) extract for a longer period of time (noted by Dan). Grinding finer may extract more caffeine, but it's probably a minor effect compared to the above.*

Different people have very different physiological responses to caffeine. Depending on the conditions under which you ingest it, your particular response to caffeine can vary as well.

Have you considered that the blend itself has changed since you last ordered it? Coffee is an agricultural product, so this is also a distinct possibility.

* I'm basing this statement on measurements of caffeine in various coffee beverages. Espresso is reported to have less caffeine than e.g. drip or French press, despite the finer grind.

HB wrote:Does the brew ratio of espresso made from your older coffee also change (e.g., from double to ristretto range)?

I haven't calculated brew ratio, but I generally pull until I produce the same volume in the cup.

RapidCoffee wrote:Absolutely. But here's my reasoning: there's no way for additional caffeine to get into the roasted coffee. To get more caffeine in the cup, you need to a) use more coffee; b) extract at a hotter temperature; or c) extract for a longer period of time (noted by Dan). Grinding finer may extract more caffeine, but it's probably a minor effect compared to the above.*

Agreed. I'm not suggesting that the amount of caffeine in the beans would increase. I suppose, what I'm wondering is that since the ratio of caffeine to what I'm calling desirable solubles (sugars, aromatics, etc. All the stuff that makes espresso interesting and complex.) presumably becomes greater as those solubles break down, whether that's enough to affect the caffeine in the cup.

This is based on the assumption that, as the coffee begins to go stale it will lose some of its desirables, but that the amount of caffeine in the bean will stay the same.

RapidCoffee wrote:Different people have very different physiological responses to caffeine. Depending on the conditions under which you ingest it, your particular response to caffeine can vary as well.

Have you considered that the blend itself has changed since you last ordered it? Coffee is an agricultural product, so this is also a distinct possibility.

I'd thought of both of these as well. Clearly, either (or both) of these explanations are more likely to be the correct one for my perceived change in the effects.

brokemusician77 wrote:I haven't calculated brew ratio, but I generally pull until I produce the same volume in the cup.

How do your extraction time and dose change as compared to using 1-week-old coffee? You probably are extracting more from the coffee (longer contact time, finer ground/more surface area), and using more coffee. So I think there's some logic to your reasoning. But the way you framed it in the topic title almost makes it sound like the beans are getting more caffeinated as they sit on your shelf (highly improbable).

A question for the coffee physicists among us:

If CO2 is a solvent that is efficient at extracting caffeine from coffee beans (as described here and here), then wouldn't fresh coffee that introduces more CO2 into the extraction tend to give up more caffeine than coffee which has already outgassed most of its CO2?

I would begin by questioning the subject concerning stomach contents- the amount of food or other liquid in the digestive tract would (could? [might??]) affect the rate of caffeine absorption, and this could explain the perception that the coffee has more caffeine.