Fun without the Buzz: Decaffeination Processes and Issues
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. The trick, of course, is how to take out the caffeine without also removing the various components that give coffee its very complex flavor.
Traditional or European Process
In the process variously called the solvent process, European process, traditional process or conventional process, that trick is accomplished through the use of a solvent that selectively unites with the caffeine. There are two variants to the solvent approach.
The direct solvent process opens the pores of the beans by steaming them and applies the solvent directly to the beans before removing both solvent and caffeine by further steaming. The indirect solvent process first removes virtually everything, including the caffeine, from the beans by soaking them in hot water, then separates the beans and water and strips the caffeine from the flavor-laden water by means of the caffeine-attracting solvent. The solvent-laden caffeine is then skimmed from the surface of the water, and the water, now free of both caffeine and solvent, is reunited with the beans, which soak up the flavor components again. The beans are then dried and sold.
With both direct and indirect solvent methods the caffeine is salvaged and sold to makers of pharmaceuticals and soft drinks.
Solvents currently in use are methylene chloride and ethyl acetate. Neither has been fingered as a health threat by the medical establishment, although methylene chloride has been implicated in the depletion of the ozone layer. Ethyl acetate is found naturally in fruit, so you may see coffees decaffeinated by processes making use of it called natural process or naturally decaffeinated.
Note that both methylene chloride and ethyl acetate evaporate very easily. Even if small amounts of solvent remain in the beans, it is highly unlikely that significant residues survive the high temperatures of the roasting and brewing processes that occur before the coffee is actually drunk. Nevertheless, consumers' almost metaphysical fear of such substances has led to the commercial development of alternative processes.
Swiss-Water or Water-Only Process
There are two phases to this commercially successful process. In the first, start-up phase, green beans are soaked in hot water, which removes both flavor components and caffeine from the beans. This first, start-up batch of beans is then discarded, while the caffeine is stripped from the water by means of activated charcoal filters, leaving the flavor components behind in the water and producing what the Swiss-Water Process people call "flavor-charged water" -- water crammed full of the goodies but without the caffeine. This special water becomes the medium for the decaffeination of subsequent batches of green beans.
When soaked in the flavor-charged but caffeine-free water, new batches of beans give up their caffeine but not their flavor components, which remain more or less intact in the bean. Apparently the water is so charged with flavor components that it can absorb no more of them, whereas it can absorb the villainous caffeine.
Having thus been deprived of their caffeine but not their flavor components, the beans are then dried and sold, while the flavor-charged water is cleaned of its caffeine by another run through charcoal filters and sent back to decaffeinate a further batch of beans.
The problem with this process from a specialty coffee point of view is the fact that the flavor components of various batches of beans may become a bit blurred. If your coffee is an Ethiopia, for example, and yesterday's batch was a Colombia, it may be hard to determine exactly whose flavor components actually inhabit the bean at the end of the process. Your Ethiopia may end up with a little of yesterday's Colombia in it, whereas tomorrow's Costa Rica may end up with a little of your Ethiopian, and so on.
The Swiss-Water people apparently have various ways of correcting for this problem, however, and over the years have steadily improved the quality of their product. This success, combined with the encouraging fact that no solvent whatsoever is used in the process and the reassuring ring of "Swiss-Water," with its associations of glaciers, alpine health enthusiasts, and chewy breakfast cereal, have combined to make this process the most popular of the competing decaffeination methods among specialty coffee consumers
Carbon Dioxide or CO2 Process
In this method, the green beans are bathed in highly compressed carbon dioxide (CO2), the same naturally occurring substance that plants consume and human beings produce. In its compressed form the carbon dioxide behaves partly like a gas and partly like a liquid, and has the property of combining selectively with caffeine. The caffeine is stripped from the CO2 by means of activated charcoal filters.
Choosing Coffee by Decaffeination Method
If you are concerned only about health issues, I suggest that you buy the decaffeinated coffee that tastes good to you, regardless of process. Given the temperature at which all currently used solvents evaporate, it does not appear likely that enough of the chemical could possibly survive the roasting and brewing processes to be anything more than the tiniest pea under the health-conscious consumer's mattress.
If, however, you are concerned about the environment, there may be some reason to avoid coffees decaffeinated by methods using methylene chloride, which has been plausibly accused of attacking the ozone layer. Choose instead coffees decaffeinated by the Swiss Water method, by solvent methods using ethyl acetate, or by CO2 processes. Coffees decaffeinated by the Swiss- Water method are usually (though not always) so labeled. Signs and labels typically identify CO2- decaffeinated coffees as well. When no decaffeination method is indicated, a good guess is that the coffee has been decaffeinated by a method involving use of a solvent.
Decaffeination and Flavor
Since caffeine in itself is virtually tasteless, coffee flavor should not be affected by its removal. However, in the process of its removal, coffee beans are subjected to considerable abuse, including (depending on the process) prolonged steaming and exposure to solvent or soaking in hot water and/or liquid CO2. Consequently, most caffeine-free coffees are difficult to roast, which I find is usually the problem with disappointing decaffeinated coffees rather than the impact of the decaffeination itself.
Which method influences coffee flavor least?
It is difficult to say for two reasons. First, it is virtually impossible to find the identical coffee decaffeinated by a range of different methods, and the character of the original coffee obviously influences the character of the final cup. Second, decaffeinated coffees are difficult to roast properly, and any subtle differences in decaffeination method may be overwhelmed by differences in the quality of the roast.
Nevertheless, my own experience suggests that the Swiss Water Process tends (emphasis on tends) to develop body while muting acidity and high notes, whereas the European or solvent process tends to preserve acidity, nuance, and high notes, but may reduce body and dimension. As for coffees processed using the CO2 method, I have tasted some excellent samples but not enough of them to generalize.
The above material is adopted from the books Coffee: A Guide to Buying, Brewing & Enjoying and Espresso: Ultimate Coffee, both by Kenneth Davids and published by St. Martin's Press. Available on www.espresso101.com; click on Coffee Business Books.