Doctor Poison might have risen to Goethe’s challenge and discovered caffeine, but the solution to the playwright’s sleep problem was almost a century away and was discovered by accident. Caffeine, a white, bitter-tasting powder in its pure state, is soluble and can be extracted by waterlogging a green, unroasted coffee bean. When German coffee merchant, Ludwig Roselius, took delivery of a shipment of coffee beans in 1903 that had been soaked, he was loathe to throw it away. Instead, after processing some of the beans, he found that the drink tasted and smelt like coffee, just minus the caffeine which the seawater had washed out.
Replacing seawater with benzene, a chemical that, at the time, was used in paint strippers and aftershave, Roselius developed a process for decaffeinating coffee beans which enabled his company, Kafee HAG, to become the first, in 1905, to offer instant decaf coffee on a commercialised basis. Benzene, though, is a known carcinogen and nowadays coffee merchants, who use a chemical-based method to extract caffeine, deploy either methylene chloride, itself toxic if humans are exposed to high quantities, or ethyl acetate.
The green coffee beans are either soaked in hot water and then washed in a chemical solution (the indirect-solvent process) or steamed for about thirty minutes, then washed in the chemical solvent before being steamed again to remove any solvent traces (the direct-solvent process). Purists claim that exposing the beans to hot water, either directly or as steam, damages their natural oils and flavours before the start of the extraction process.
More recently two non-solvent-based methods for extracting caffeine have been developed, the earliest of which to be used commercially, the Sparkling Water method, was also discovered by accident. In 1967 Kurt Zosel, a chemist at the Max Planck Institute for Coal Research in the Ruhr, was working with carbon dioxide and discovered that when the gas is heated and put under pressure, it can be used for separating different chemical substances.
The beans are gently moistened which causes them to expand and widen their pores, giving the more mobile caffeine molecules more room in which to move. They are then washed over with a natural carbon dioxide solution which eases out the caffeine, a process which produce little waste, is completely chemical-free, and does not damage the flavour of the coffee.
Alternatively, the Swiss Water Process, developed in Switzerland in 1933 but not used commercially until 1979 by Coffex S A, uses a heated proprietary Green Coffee Extract (GCE) which contains all the water-soluble compounds found in coffee, except caffeine. The green beans are soaked in it, causing them to swell, expelling the caffeine molecules into the GCE while retaining the more volatile taste and smell compounds. This process can take between eight to ten hours before all the caffeine is removed. While the GCE can be reused for the next batch, critics point out that by doing so the unique qualities of a particular batch of beans can be compromised.
Decaf coffee beans look different from their caffeinated confrères, shinier and darker in colour, a consequence, Andy Cross of Two Chimps Coffee explains, of their drying process, during which, while heated, they rub against and polish each other, creating their characteristic sheen. However, the colour adds to the roaster’s difficulty in judging when they are ready as does their reduced bound water content which accelerates the speed at which they roast. Nonetheless, if decaffeinated well and in the hands of a skilled roaster, decaf coffee will taste just as delicious as regular coffee. I wonder what Goethe and Doctor Poison would have made of it all.