What is decaffeinated coffee?
Decaffeinated coffee is available as a choice for those consumers who wish to enjoy the taste and aroma of coffee without experiencing the mild stimulant effects provided by the caffeine.
Cup Quality of Decaffeinated Coffee
The cup quality of decaffeinated coffee is fully in line with that of regular coffee. Indeed, all the many different coffee varieties and origins retain their specific flavour properties.
The Decaffeination Processes
The decaffeination processes are performed on green coffee beans in industrial plants.
There are four methods of decaffeination, according to which substance is used to extract the caffeine; Water – Ethyl Acetate – Supercritical or Liquid CO2 – Methylene Chloride.
These four processing methods all share the basic stages of;
- Swelling the green coffee beans with water or steam in order to make the caffeine available for extraction
- Extracting the caffeine from the beans
- Steam stripping to remove all solvent residues from the beans (when applied) / regenerating adsorbents (when applied)
- Drying the decaffeinated coffee beans back to their normal moisture content
Under carefully controlled process conditions, such as temperature, pressure and time, the caffeine extraction step is based on physical phase transport mechanisms. Due to the difference in concentration, the caffeine is diffused out of the cell structure into solvent surrounding the bean until the concentration of caffeine is the same inside and outside the beans.
The Decaffeination Methods
What really distinguishes the four methods is the choice of substance used for extraction;
- Water method; When green coffee is immersed in water the caffeine content is dissolved and removed, but along with this much of the coffee’s aromatic character can be lost.
To overcome this drawback, the liquid is saturated with the water-soluble components of the coffee.
The caffeine is subsequently removed from the solution using activated carbon or other adsorbents, which retain the caffeine, and the extract deprived of the caffeine can then be recycled.
- Ethyl - Acetate method: Ethyl - Acetate (EA) occurs in several natural products and contributes to the characteristic aroma of many fruit.
EA is also found in varying concentrations in foodstuffs including green and roasted coffee.
In the decaffeination process the combination of water and ethyl-acetate is used.
In the extracting vessel the EA is circulated around the water soaked beans for extracting the caffeine.
Then the mixture of water, ethyl-acetate and caffeine is drained from the extracting vessel.
The extraction step is repeated several times, until the residual caffeine content is at or below the legal maximum level of 0,1%.
- Supercritical Carbon Dioxide and Liquid Carbon Dioxide method: CO2 is a readily available substance of great purity, naturally available in the air we breath and in the sparkling water we drink.
Under certain conditions it allows for a selective caffeine extraction and leaves most of the other coffee bean constituents unaltered.
The use of carbon dioxide in its supercritical state (between its liquid and gaseous state) needs very high pressure – up to 250 atmospheres. This method requires large-scale production in order to be economically viable.
Also, liquid CO2 can be used for caffeine extraction with lower pressure and lower temperatures, wherefore a longer time is necessary to achieve the extraction.
- Methylene Chloride (i.e. Dichloromethane-DCM) method: DCM extracts the caffeine selectively and has a low boiling point. In the extracting vessel dicloromethane is circulated around the water soaked beans for extracting the caffeine. Then the mixture of DCM and caffeine is drained from the extracting vessel. The extraction step is repeated several times, until the residual caffeine content is at or below the legal maximum level of 0,1%. The process followed guarantees that possible solvent residues remain below the limits fixed by the European legislation.
Source: COSIC Coffee Science Information Centre