Decaffeinated coffee contains, at most, one fortieth of the amount of caffeine in untreated beans. The removal of caffeine should not alter the taste of coffee. Isolated, caffeine is a crystalline substance lacking aroma and possessing only the slightest bitter taste. The only real problem is how to take out the caffeine without ruining the rest of what does influence coffee flavor. But technology has triumphed, more or less. The best decaffeinated coffee, freshly roasted and ground and carefully brewed, can taste so nearly the equal of a similar untreated coffee that only a tasting involving direct comparison reveals the difference.
Coffee is decaffeinated in its green state, before the delicate oils are developed through roasting. Hundreds of patents exist for decaffeination processes, but only a few are actually used. Decaffeination plants are enormously expensive facilities to build, and the processes used are sophisticated, costly, and time-consuming. More important, to end up with decent decaf you have to start with superlative green coffee beans. Every decaffeination process strips a great deal of flavour from the coffee; if you want a product with any kind of flavour post-decaffeination, you have to invest in the highest-quality and therefore most expensive beans. The goal of all decaf processors has been only to remove the caffeine, not the flavour. It is the quality of beans that will ultimately determine the flavour of the coffee.
The Solvent or Traditional Process
The direct solvent method is the oldest and most common decaffeination process. The beans are first steamed to open their pores, and then soaked in an organic solvent that selectively unites with the caffeine. The beans are then steamed again to remove the solvent residues, dried, and roasted like any other green coffee.
A more recently developed process called the indirect solvent method starts by soaking green beans in near-boiling water for several hours. The water is transferred to another tank, where it is combined with a solvent that selectively absorbs most of the caffeine. The caffeine-laden solvent is then skimmed from the water, with which it has never really mixed.
The water, now free of both caffeine and solvent, still contains oils and other materials important to flavor. In order to return these substances to the beans, the water is returned to the first tank, where the beans reabsorb the flavor-bearing substances from the water.
The Swiss Water Process
In the 1980s the Swiss firm Coffex S.A. developed a commercially viable decaffeination process using water only. The various chemical constituents of the green coffee, including the caffeine, are first removed by soaking the beans in very hot water. The water is stripped of its caffeine, not by a solvent, but by percolation through activated charcoal. The beans are returned to the hot water, where they reabsorb the remaining, caffeine-free flavor constituents from the water.
This process is more costly than the solvent process because the separated caffeine cannot be recovered from the charcoal and sold separately, as it is with the two solvent methods. It is also controversial in terms of flavor. Many coffee professionals contend that the Swiss Water Process blurs flavor more than the competing solvent processes. However, the management of the Canadian plant that currently produces all of the Swiss Water Decaffeinated coffees sold in North America continues to make determined efforts to refine and improve the process.
The Carbon Dioxide (CO2) Process
The Carbon Dioxide process takes advantage of the fact that CO2, when compressed, behaves partly like a gas and partly like a liquid, and has the property of combining selectively with caffeine. The steamed beans are bathed in the compressed carbon dioxide and the caffeine is removed from the carbon dioxide through charcoal filtering, just as it is in the water-only process. However, the flavor components remain in the bean throughout the process, rather than being soaked out and then put back in again.
Since carbon dioxide is the same ubiquitous and indisputably "natural" substance that plants absorb and humans produce, and since, in most versions of the CO2 method, the flavour components remain safely in the bean throughout the process, carbon dioxide methods would seem to be the decaffeinating wave of the future.