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I actually work directly with food scientists. I'll ask somebody when I'm feeling more myself!

And yes! I learned how to do it yesterday. It's dummy simple. The most course grind possible is what appears to be recommended. You brew 1 part coffee to 4 parts water in the fridge for 12–18 hours. Then you just strain it. I do not recommend rapid consumption 💀

EDIT: Yeah, it's the duration. Hot brewed coffee has a not-insignificant amount of caffeine because a smaller grind puts more surface area in contact with water at any given time, and the hot water accelerates extraction of caffeine (and flavor) from the grounds. Cold brewed coffee blows that out of the water, even with a super coarse grind and even at super low temperatures, by virtue of the time involved.