How to extract caffeine from coffee
The popular procedure to experimentally isolate caffeine is sublimation.

Slowly heat a teaspoon of coffee or tea from 150°C to 250°C. Let the sublimated caffeine precipitate at a watch glass cooled with ice. The resublimated caffeine forms white needles that can be identified under a microscope.

The sublimation temperature of caffeine is 178°C.