Every morning, millions of people yearn for their first cup of coffee to get them going! With or without milk, this beverage is widely consumed worldwide, across countries and cultures.
However, health concerns regarding excessive consumption of caffeine mean many are turning to decaffeinated alternatives. From the original use of benzene, the process of decaffeination has improved much since the early 20th century when the first procedure was proposed.
The main objective of current methods is to obtain a product with less than 3% of the original caffeine, but importantly without affecting any other components responsible for the coffee’s characteristic flavour and aroma. Typically, methods depend on various solvents to remove caffeine from green coffee beans, and can be classed as direct, where the solvent enters in contact with the coffee beans; or indirect, where the beans remain solvent-free. Following this treatment, coffee beans are ready to be roasted and sent to market to be enjoyed by millions of coffee lovers.
These methods rely on direct contact between solvent and coffee beans, to remove caffeine. Solvents used are carefully selected to show a great affinity exclusively to caffeine, without affecting the coffee beans in any other way. In other words, caffeine is more soluble in the solvent than in water, but other compounds remain in the original solution. Traditionally, the most popular solvent is methylene chloride, but effective decaffeination can also be achieved with ethyl acetate or CO2.
The use of ethyl acetate is often claimed to be “natural”, as this compound is present naturally in many fruits and vegetables. In addition, companies keen to avoid the use of strong chemicals perceived by the public as dangerous have started using CO2 at high pressure and high temperature forming a solution between gas and liquid. In this condition, CO2 molecules are extremely good at dragging small caffeine molecules, without affecting other larger and heavier compounds.
These methods are more expensive and time-consuming to carry out, but some consumers prefer the safety they can provide. In contrast to previous examples, indirect processes are characterised by a complete separation between solvent and beans, achieved by a two-step process.
The first step involves the production of a strong coffee extract, obtained by soaking green coffee beans in water, dissolving not only caffeine but also many other important coffee constituents, and the subsequent removal of caffeine from this solution. This can be achieved using the same solvents as described earlier, including methylene chloride and ethyl acetate. Recently, a new method has been developed relying on carbon filters to trap caffeine and refusing the presence of any chemical at all.
During the second step, a new batch of green coffee beans is added to this caffeine-free coffee extract. From a chemical point of view, all compounds in the coffee bean are in equilibrium with the solution, except for caffeine, which can safely dissolve from the beans. The results are decaffeinated coffee beans that have never been in contact with any solvent.
Interestingly, researchers are attempting to move away from chemical-based decaffeination and develop a caffeine-free coffee plant. This may not be as far-fetched as you may think! Although zero-caffeine is still in the land of dreams, plants with extremely low concentrations of caffeine have been developed. Maybe in the near future, you can reach for a cup of coffee without worrying about the health consequences of ingesting too much caffeine.