For many people, the aroma of freshly brewed coffee is the start of a great day. But Caffeine can cause headaches and nervousness in others. That’s why many people opt for a decaffeinated cup instead.
I am a chemistry teacher. who has lectured on why chemicals dissolve in some liquids and not others. Decaffeination processes provide good concrete examples of these chemical concepts. However, even the best decaffeination method, does not eliminate all caffeine – There are typically 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 flavor and aroma chemicals. Decaffeination has a rich historyand now almost all coffee producers use one of three common methods.
All these methods, which are also used to make decaffeinated tea, Start with green or unroasted coffee beans that have been pre-moistened. Using roasted coffee beans would result in a coffee with a very different aroma and taste, as decaffeination steps would remove some flavor and odor compounds produced during roasting.
The carbon dioxide method
In the relatively new carbon dioxide method, developed in the early 1970s, producers use high-pressure CO₂ to extract caffeine from moistened coffee beans. They pump the CO₂ into an airtight container containing the moistened coffee beans, and the caffeine molecules dissolve in the CO₂.
Once the caffeine-laden CO₂ is separated from the beans, producers pass the CO₂ mixture either through a container filled with water or over a bed of activated carbonActivated charcoal is charcoal that has been heated to a high temperature and exposed to steam and oxygen, which creates pores in the charcoal. This step filters out caffeine and most likely other chemical compoundssome of which affect the flavor of the coffee.
These compounds bind to the pores of the activated carbon or remain in the water. Producers dry the decaffeinated beans using heat. Under the effect of heat, the remaining CO₂ evaporates. Producers can then repressurize and reuse the same CO₂.
This method removes 96% to 98% of caffeineand the resulting coffee contains only minimal CO₂ residue.
This method, which requires expensive equipment for the production and handling of CO₂, is largely used to decaffeinate commercial or supermarket grade coffees.
Swiss water process
The Swiss water method, initially used commercially in the early 1980sUse hot water to decaffeinate coffee.
First, producers soak a batch of green coffee beans in hot water, which helps extract caffeine and other chemical compounds from the beans.
It’s a bit like what happens when you brew roasted coffee: you put dark beans in clean water, and the chemicals that give the coffee its dark color leach out of the beans into the water. Similarly, hot water extracts caffeine from beans that haven’t been decaffeinated yet.
During steeping, the concentration of caffeine in the coffee beans is higher than in the water, so the caffeine passes from the beans to the water. Producers then take the beans out of the water and place them in fresh water, which does not contain caffeine. So the process repeats itself and more caffeine comes out of the beans and passes into the water. Producers repeat this process, up to 10 times, until there is almost no caffeine left in the beans.
The resulting water, which now contains the caffeine and all the aromatic compounds dissolved in the beans, passes through activated carbon filters. These trap the caffeine and other chemical compounds of similar size, such as sugars. and organic compounds called polyamineswhile allowing most other chemical compounds to remain in the filtered water.
Producers then use the filtered water, saturated with flavor but stripped of most of the caffeine, to steep a new batch of coffee beans. This step allows the flavor compounds lost during the steeping process to reintegrate into the beans.
THE Swiss water process is valued for its chemical-free approach and ability to preserve most of the coffee’s natural flavor. This method It has been shown to remove 94-96% caffeine.
Solvent-based methods
This traditional and most common approach, first performed in the early 1900suses organic solvents, which are liquids that dissolve organic chemicals such as caffeine. Ethyl acetate and methylene chloride are two common solvents used to extract caffeine from green coffee beans. There are two main solvent-based methods.
In the direct method, producers soak wet beans directly in the solvent or in an aqueous solution containing the solvent.
The solvent extracts most of the caffeine and other chemical compounds with similar solubility to caffeine from the coffee beans. Producers then remove the beans from the solvent after about 10 hours and dry them.
In the indirect method, producers soak the beans in hot water for a few hours and then remove them. They then treat the water with a solvent to extract the caffeine. Methylene chloride, the most common solvent, does not dissolve in water, so it forms a layer on the surface of the water. Caffeine dissolves better in methylene chloride than in water, so most of the caffeine remains in the methylene chloride layer, which producers can separate from the water.

Andy Brunning/Compound Interest, CC BY-NC
As in the Swiss water method, producers can reuse the “caffeine-free” water, which can restore some of the flavor compounds removed in the first step.
These methods remove about 96% to 97% caffeine.
Is decaf coffee safe to drink?
Ethyl acetate, one of the most common solvents, occurs naturally in many foods and beverages. It is considered a safe chemical for decaffeination by the Food and Drug Administration.
The FDA and the Occupational Safety and Health Administration have deemed methylene chloride unsafe to consume at concentrations greater than 10 milligrams per kilogram of body weight. However, the amount of residual methylene chloride found in roasted coffee beans is very small – about 2 to 3 milligrams per kilogram. It is well below FDA limits.
OSHA and its European counterparts have strict rules in the workplace to minimize exposure to methylene chloride of workers involved in the decaffeination process.
After decaffeinating coffee beans with methylene chloride, producers steam and dry them. The coffee beans are then roasted at high temperatures. During the steaming and roasting process, the beans become hot enough for the residual methylene chloride to evaporate. The roasting step also produces new aromatic chemicals from the breakdown of chemicals into other chemicals. These give coffee its distinctive flavor.
Additionally, most people brew their coffee in between 190°F and 212°Fwhich provides another opportunity for the methylene chloride to evaporate.
Preserve aroma and flavor
It is chemically impossible to dissolve only caffeine without also dissolving other chemical compounds present in the beans. So decaffeination inevitably removes some of the other compounds that contribute to the aroma and flavor of your cup of coffee.
But some techniques, such as the Swiss water process and the indirect solvent method, have steps that can reintroduce some of these extracted compounds. These approaches probably can’t return all of the extra compounds to the beans, but they can reintroduce some flavor compounds.
With these processes, you can enjoy that delicious cup of coffee without the caffeine – unless your server accidentally switches the pots.