coffee beans and decaf
(picture found on) https://medlineplus.gov/caffeine.html
to decaffeinate coffee they add a solvent, usually methylene chloride, to green coffee beans which dissolves a portion of the caffeine. after this the solvent is evaporated along with some of the caffeine and this process is repeated until the caffeine content is down to acceptable standards. There are different approaches but they are all generally done like this.