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There are five different processes. They all start with the same step: pouring the coffee beans into hot water to soften them, then soaking them in a solvent. One of the more traditional methods uses methylene chloride, a substance that binds to caffeine molecules, extracting them from the grain.
Another possible substance is ethyl acetate. The problem with these first two methods is that the solvent is never completely removed from the coffee, which tastes different. A third method is, after softening the beans, cooking them with carbon dioxide in a high-pressure boiler.
Under these conditions, carbon dioxide attracts small caffeine molecules. The molecules that contain the coffee flavor, being larger, are not removed and the taste of the drink is better preserved. Its disadvantage is that it is an expensive method. The fourth alternative is to use hot water itself as a solvent. The coffee stays in it until several of its substances, both caffeine and flavor molecules, float.
After passing through a charcoal filter, which retains only the caffeine, the water is returned to the grains, which reabsorb the flavor molecules. The fifth method is a variation of the last one. Instead of soaking the beans in pure water, water already saturated with coffee substances and filtered through charcoal is used. Thus, only the caffeine is drawn out of the beans, as the flavor molecules cannot find space to be absorbed by the water.