In my experience, judging from the subjective felt effect when drinking it, the amount of caffeine in filter coffee can vary by a factor 3x depending on brewing technique. I just came back from the U.K. and the hotel breakfast coffee there did less for me in three cups than a single cup from my Fellow Aiden coffee brewer at home. I used to cold brew coffee but had to stop because the apparently higher caffeine content gave me heart problems.
In my experience, judging from the subjective felt effect when drinking it, the amount of caffeine in filter coffee can vary by a factor 3x depending on brewing technique. I just came back from the U.K. and the hotel breakfast coffee there did less for me in three cups than a single cup from my Fellow Aiden coffee brewer at home. I used to cold brew coffee but had to stop because the apparently higher caffeine content gave me heart problems.