Fourteen-year-old Ross from Dartmouth asks a question that has probably occurred to many readers. Ross wonders how coffee manufacturers make decaffeinated coffee.
To be labelled “decaffeinated”, at least 97 per cent of the caffeine must be removed, but since only about 1 per cent of a coffee bean is caffeine, removal is an intricate process. One relatively new method is to heat Co2 gas with liquid Co2 under high pressure until the density of the two states is the same, then force this supercritical Co2 through green coffee beans to dissolve the caffeine.
Older methods use chemical solvents like ethyl acetate and methylene chloride. In one procedure, the beans are steamed to loosen the caffeine molecules, then repeatedly rinsed in the solvent, drained, then steamed again in fresh water so that no trace of either the caffeine or the chemical agent remains. Then the beans are dried..
In another process, the beans are soaked in hot water long enough to remove all their caffeine, then taken out and a chemical agent added to extract the caffeine from the water. The solution is heated until the chemical and the caffeine have evaporated. The caffeine-free water that remains still contains the flavour, so the beans are soaked in it again, then removed and dried.
Some brands market a “naturally decaffeinated” product, so-called because the beans are water-soaked to draw out the caffeine; then carbon filters, instead of chemical additives or carbon dioxide, are used to extract the caffeine from the water. In this process too the beans are soaked in the caffeine-free water to reabsorb the flavours before being dried and marketed.
Sometimes, oil from the coffee grounds of these decaffeinated beans is recycled. Fresh, green beans are kept in these oils at a high temperature. When the oils have attracted all the caffeine from the beans, they become a new batch of decaffeinated coffee beans, ready for us to enjoy.
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