To make decaf coffee, companies soak green coffee beans in hot water (70-100 degrees Celsius/160-210 degrees Fahrenheit) to soften them and draw out the water-soluble caffeine molecules. Depending on the method, the water bath might contain a chemical solvent like methylene chloride or ethyl acetate that clings to the caffeine molecules and then evaporates out of the solution.
Another method soaks the beans under very high pressure and temperature, using liquid CO2 as a ‘natural’ solvent that bonds with the caffeine. The most natural method uses only water treated with coffee oils to draw out the caffeine gradually in batches. Once the green coffee liquid is at least 98 per cent caffeine free, it is soaked up again by the coffee beans, which are dried, roasted and bagged for sale.
Answered by Dave Roos.