For many people, the smell of freshly brewed coffee is the start of a great day. But for others, caffeine can cause headaches and jitters. That’s why many people reach for a cup of decaf instead.
I am a chemistry professor who has lectured on why chemicals dissolve in some liquids but not others. The processes of decaffeination provide great real-life examples of these chemical concepts. However, even the best decaffeination method does not remove all of the caffeine: there is usually about 7 milligrams of caffeine left in an 8-ounce cup.
Producers who decaffeinate their coffee want to remove the caffeine while retaining all (or at least most) of the other chemical aroma and flavor components. Decaffeination has a rich history, and today almost all coffee producers use one of three common methods.
All of these methods, which are also used to make decaffeinated tea, start with green or unroasted coffee beans that have been pre-soaked. Using roasted coffee beans would result in a coffee with a very different aroma and flavor, as the decaffeination steps would remove some of the flavor and odor compounds produced during the roasting process.
The carbon dioxide method
In the relatively new carbon dioxide method, developed in the early 1970s, manufacturers use high-pressure CO₂ to extract caffeine from moistened coffee beans. They pump the CO₂ into a sealed container with the moistened coffee beans, and the caffeine molecules dissolve into the CO₂.
Once the caffeinated CO₂ is separated from the beans, producers pass the CO₂ mixture through a tank of water or over a bed of activated carbon. Activated carbon is carbon that has been heated to high temperatures and exposed to steam and oxygen, which creates pores in the carbon. This step filters out the caffeine, and most likely other chemical compounds as well, some of which affect the flavor of the coffee.
These compounds bind into the pores of the activated carbon or remain in the water. Producers dry the decaffeinated beans using heat. Under the heat, any remaining CO₂ evaporates. Producers can then repressurize and reuse the same CO₂.
This method removes 96 to 98 percent of the caffeine and the final coffee contains only minimal CO₂ residue.
This method, which requires expensive equipment to create and process CO₂, is widely used to decaffeinate commercial or supermarket coffee.
Swiss water process
The Swiss water method, first used commercially in the early 1980s, uses hot water to decaffeinate coffee.
First, producers soak a batch of green coffee beans in hot water, which extracts both the caffeine and other chemical compounds from the beans.
It’s a bit like what happens when you brew roasted coffee beans: you put dark beans in clear water and the chemicals that give the coffee its dark color leach out of the beans into the water. In a similar way, the hot water extracts the caffeine from beans that haven’t been decaffeinated.
During the steeping process, the caffeine concentration in the coffee beans is higher than in the water, so the caffeine is released from the beans into the water. Producers then remove the beans from the water and place them in fresh water, which does not contain caffeine. The process repeats itself, and more caffeine is released from the beans into the water. Producers repeat this process, up to 10 times, until there is almost no caffeine left in the beans.
The resulting water, now containing the caffeine and all the flavor compounds dissolved from the beans, is passed through activated carbon filters. These trap caffeine and other similarly sized chemical compounds, such as sugars and organic compounds called polyamines, while leaving most of the other chemical compounds in the filtered water.
Producers use the filtered water, saturated with flavor but stripped of most of the caffeine, to soak a new batch of coffee beans. This step reintroduces the flavor compounds lost during the soaking process.
The Swiss Water Process is praised for its chemical-free approach and its ability to retain most of the coffee's natural flavor. This method has been shown to remove 94 to 96 percent of the caffeine.
