Hide the package and most people would not know from taste alone if a coffee was decaffeinated.

­- The Complete Guide to Coffee

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.

"Decaffeinating Coffee

An article from "Scientific America" by Saul N. Katz (June 1997)

CAFFEINE is a small, bitter-tasting alkaloid. High-quality Arabica coffee beans (the source of most specialty coffees) are typically 1 percent caffeine by weight, whereas cheaper and more bitter Robusta beans have twice that amount.

Spurred by the belief that excessive coffee drinking had poisoned his father, the German chemist Ludwig Roselius, in about 1900, found a number of compounds that dissolved the natural caffeine in coffee beans without ruining the drink's taste. Chloroform and benzene did the job but were toxic, so for 70 years methylene chloride became the solvent of choice.

When it was discovered in the 1980s to be a suspected carcinogen, the chemical was abandoned by all the big U.S. coffee labels. The Food and Drug Administration continues to permit the use of methylene chloride if the residues in the coffee are below 10 parts per million. Processing for specialty decafs still often uses it because it perturbs other flavorings so little.

Many other solvents can serve to debuzz coffee. An "all-natural" label may mean that ethyl acetate is the solvent in use, because that chemical occurs naturally in fruit. Water also works as a means of decaffeination. The so-called Swiss water process soaks green coffee beans in a solution that contains the chemical components of beans dissolved from a previous batch, except for the caffeine. Because the water is already saturated with sugars and peptides, only the caffeine passes from the beans into the water.

Another process, illustrated here, uses supercritical carbon dioxide as a solvent; in this state, the carbon dioxide is intermediate between a gas and a liquid. The variety of caffeine extraction methods demonstrates that a lot of sleepless nights have gone into helping the world get a good night's rest.

1. Soaking green coffee beans in water doubles their size, allowing the caffeine to dissolve into water inside the bean.
2. Caffeine removal occurs in an extraction vessel, which may be 70 feet high and 10 feet in diameter, suffused with carbon dioxide at roughly 200 degrees Fahrenheit and 250 atmospheres. Caffeine diffuses into this supercritical carbon dioxide, along with some water. Beans enter at the top of the chamber and move toward the bottom over five hours. To extract the caffeine continuously, the beans lower in the column are exposed to fresher carbon dioxide, which ensures that the caffeine concentration inside beans is always higher than in the surrounding solvent. Caffeine therefore always diffuses out of the beans.
3. Decaffeinated beans at the bottom of the vessel are removed, dried and roasted.
4. Recovery of dissolved caffeine occurs in an absorption chamber. A shower of water droplets leaches the caffeine out of the supercritical carbon dioxide. The caffeine in this aqueous extract is then often sold to soft-drink manufacturers and drug companies. The purified carbon dioxide is recirculated for further use.

SAUL N. KATZ retired in 1989 as a principal scientist at the Maxwell House Division of General Foods. He holds several patents on the process for supercritical fluid extraction of caffeine.

Sourced from the Scientific American