Traditional or European
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
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
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
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
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
Carbon Dioxide or CO2
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
Choosing Coffee by Decaffeination
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
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
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.
Davids is a coffee expert, author, and co-founder of the Coffee
Review. 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.