On the other hand, you "boil" your coffee for 2 minutes, not 2880 minutes (48h). But I'm no chemist, so you might still be right, despite the different orders of magnitude.
Also, we're not factoring in the water/steam pressure.
Anybody volunteers for extracting coffee with an espresso machine for 48h?
This doesn't have to be academic. You can do an experiment at home. Brew a big cup of coffee with a drip machine and drink it. Note how you feel. Then, make a batch of cold brew and let it sit for 48 hours. Drink half as much of that as you did the hot brewed coffee, but pease do so slowly as some people become very uncomfortable with that amount of caffeine.
Yes, cold brewed coffee can have much more caffeine than you'd expect given the smoothness of the taste. Back when my brother managed a coffee shop, the first time I popped into his work and asked his recommendation, he didn't warn me of the caffeine content. I was well habituated to caffeine, but quickly drinking 12 or 16 oz. of cold-brewed coffee left me feeling a bit dizzy, to the point I hung around the shop for a bit to make sure I was fine to drive.
> Brew a big cup of coffee with a drip machine and drink it. Note how you feel. Then, make a batch of cold brew and let it sit for 48 hours.
Nah, too many variables.
What I'm getting at is: if you brew identical batches with identical methods, where the only variable is the temperature, which will have more caffeine in solution?
I'm willing to bet at about the 48hr mark it probably doesn't matter a whole lot, so I probably agree-ish with ya'll.
Caffeine is moderately soluble in water at room temperature (2 g/100 mL), but very soluble in boiling water (66 g/100 mL).
Caffeine is 33 times more soluble in hot water!
What matters more, then, is the concentration of coffee grounds to water, and how much of that water is left in the grounds.