Decaffeinated coffee, commonly referred to as decaf, contains less caffeine than regular coffee, but is usually not completely free from caffeine. Some decaf products contain just 1% of the original caffeine content, while others have as much as 20% of the original caffeine left.
United States standard: 97% of the caffeine removed
European Union standard: 99.9% caffeine-free by mass
Decaffeination of the coffee can be carried out using several different methods, each with its own pros and cons. The methods listed below are employed before the coffee is roasted.
Using coffee oils to remove the caffeine
The triglyceride process rely on coffee oils to remove the caffeine. It is a direct-contact method of decaffeination.
- Green coffee beans are soaked in hot water or in a hot coffee solution, to draw the caffeine closer to the surface of each bean.
- In another container, the beans are immersed in coffee oils and left to soak. These coffee oils have been obtained from spent coffee grounds and contain triglycerides.
- The beans are exposed to high temperatures for several hours to help the triglycerides to remove the caffeine.
- The beans are removed from the oils and left to dry.
Using an organic solvent to remove caffeine
The direct method
Green beans are steamed, and the steamed beans are rinsed with an organic solvent, typically ethyl acetate or methylene dichloride. The solvent extracts the caffeine. The process usually needs to be repeated 8-12 times to remove 97% of the original caffeine.
The indirect method
- Coffee beans are soaked in hot water for several hours, which essentially creates a very strong pot of coffee.
- The beans are removed. The remaining liquid is treated with ethyl acetate or methylene dichloride to extract the caffeine. The caffeine can then be separated from the organic solvent by evaporation.
- The same water is recycled thorugh this two-step process with an new batch of beans. After several cycles, an equilibrium is obtained, where the beans and the water have a very similar composition except for the caffeine content. After this point, only caffeine will be removed from beans placed in the water, which means that other flavours are not lost.
Using carbon dioxide to remove the caffeine
The supercritical carbon dioxide process rely on the fact that caffeine is readily soluble in supercritical carbon dioxide.
- Green coffee beans are steamed.
- The steamed beans are placed in a high-pressure vessel.
- A mixture of water and carbon dioxide is circulated through the vessel, while the pressure is kept at 300 atm and the temperature at 65 ºC (150°F). Under such conditions, carbon dioxide is a supercritical fluid, exhibiting properties somewhere midway between a gas and a liquid. The caffeine dissolves into the supercritical carbon dioxide. (Other compounds that are important for the flavour of coffee are largely insoluble in carbon dioxide, so they stay.)
Using green coffee extract to remove the caffeine
The Swiss Water Process utilizes green coffee extract to extract caffeine from the bean. Green coffee extract is a solution containing all the water-soluble components of green coffee except caffeine.
When caffeine-rich green beans are placed in a solution where caffeine is scarce or non-existant, caffeine will be drawn from the bean and into the liquid. It is the gradiant pressure that causes molecules to move from the bean and into the solution. Since the solution is already rich in all the other water-soluble compounds, there is no pressure to draw those compounds out of the bean.
The process needs to be repeated multiple times to make the beans sufficiently decaffeinated. It usually takes 8-10 hours to obtain properly decaffeinated beans using this method.