A typical 5 ounce cup of drip coffee contains 60 – 180 mg of
caffeine while the same cup of decaffeinated coffee contains 2 – 5
mg of caffeine. One ounce of espresso, the coffee made famous for
its supposed high caffeine content, only contains 30 – 50 mg of
caffeine. A typical 12 ounce soda, depending on the manufacturer,
contains 38 – 46 mg of caffeine.
Decaffeination processes are performed on unroasted (green)
beans, but the methods vary somewhat. It generally starts with
steaming beans to soften them. They are then rinsed in a solvent
that contains as much of the chemical composition of coffee as
possible without also containing the caffeine in a soluble form. The
process is repeated anywhere from 8 to 12 times until it meets the
international standard of having removed 97% of the caffeine in the
beans or the EU standard of having the beans 99.9% caffeine free by
mass. Coffee contains over 400 chemicals important to the taste and
aroma of the final drink; and because of the complexity of coffee,
no physical process or chemical reaction will remove only caffeine
while leaving the other chemicals at their original concentrations.
In other words, you can-not decaffeinate coffee without affecting
the flavor and aroma of the final product, your cup of coffee.
There have been long term concerns about decaffeinated coffee and
cancer, mostly because of some of the chemicals used in the some
decaffeination processes. Methylene chloride is a suspected
carcinogen and researchers have tried to link its use in
decaffeination with cancer but have found no correlation, most
likely because any methylene chloride that may be left in the coffee
bean is destroyed by the coffee brewing process.
Decaffeinated coffee should be more correctly referred to as
low-caffeine coffee because all brands of decaffeinated coffee still
contain some caffeine. Coffee beans naturally contain from 1% – 2%
caffeine and even after removing 97% of the caffeine from the beans,
3% of the original caffeine remains behind. The remaining caffeine
concentration can be high enough that drinking five to ten cups of
decaffeinated coffee could deliver as much caffeine as would one or
two cups of regular coffee. Most of the caffeine removed from coffee
beans is sold to soft drink manufacturers. In other words, we take
the time & trouble to remove caffeine from our coffee and then we
consume the very same caffeine in the soft drinks we drink.
Scientists discovered a caffeine free coffee plant in 2004. Maybe
sometime in the not so distant future we will have truly natural,
caffeine free coffee but until then we are stuck with one of several
processes that produce a reasonable decaffeinated cup of coffee.
Swiss water process
The Swiss Water Process is a method of decaffeinating coffee
beans that was developed by the Swiss Water Decaffeinated Coffee
Company. To decaffeinate the coffee bean by the Swiss Water method,
a batch of green (unroasted) beans is soaked in hot water, releasing
caffeine. This process is done until all the caffeine and coffee
solids are released into the water then the beans are then
discarded. Next, the water passes through a carbon filter which
traps the caffeine molecules but allows the water and the coffee
solids to pass through. The caffeine-free water which comes through,
known as "flavor-charged" water by the company, is then put in a
similar filtration device, and new coffee beans are added. But this
time the flavor-charged water cannot remove any of the coffee solids
from the new beans and only the caffeine is released. The process
repeats, filtering out all the caffeine until the beans are 99.9%
caffeine free. These beans are removed and dried, and thus retain
most of their flavor and aroma.
In the direct method the coffee beans are steamed for 30 minutes
and then repeatedly rinsed with methylene chloride or ethyl acetate
for about 10 hours. The solvent is then drained away and the beans
steamed for an additional 10 hours to remove any residual solvent.
Sometimes coffees which are decaffeinated using ethyl acetate are
referred to as naturally process because ethyl acetate can be
derived from various fruits or vegetables but because of the volume
needed, the chemical is synthetically derived.
In the indirect method beans are soaked in hot water for several
hours, essentially making a strong pot of coffee. Then the beans are
removed and methylene chloride or ethyl acetate is used to extract
the caffeine from the water. The same water is recycled through this
two-step process with new batches of beans. Equilibrium is reached
after several cycles, where the water and the beans have a similar
composition except for the caffeine. After this point, the caffeine
is the only material removed from the beans, so no coffee strength
or other flavorings are lost. Because water is used in the initial
phase of this process, sometimes indirect method decaffeination is
referred to as "water processed" even though chemicals are used.
With the CO2 process, pre-steamed beans are soaked in a liquid
bath of carbon dioxide at a pressure of 73 to 300 atmospheres (1000
– 4500 PSI). After a thorough soaking, the pressure is reduced
allowing the CO2 to evaporate, or the pressurized CO2 is run through
a water or charcoal filter to remove the caffeine. The carbon
dioxide is then used on another batch of beans. This same process
can also be done with oxygen. This process has the advantage that it
avoids the use of potentially toxic solvents.
Green coffee beans are soaked in a hot water/coffee solution to
draw the caffeine to the surface of the beans. Next, the beans are
transferred to another container and immersed in coffee oils that
were obtained from spent coffee grounds. After several hours of high
temperatures, the triglycerides in the oils remove the caffeine, but
not the flavor elements, from the beans. The beans are separated
from the oils and dried. The caffeine is removed from the oils,
which are reused to decaffeinate another batch of beans. This is a
direct contact method of decaffeination.