Decaffeination is the process whereby caffeine is removed from green coffee beans before they are roasted. To be precise more than 97.5% of the caffeine needs to be removed in order to label a coffee as decaffeinated, according to US guidelines. There are not any naturally caffeine-free coffee trees that are currently being grown commercially, so a number of methods have been established to achieve this. Below, we have discussed some of the more well-known methods, explaining in detail how the processes work.
Mountain Water Decaffeination
Mountain Water Decaf uses clear pure waters from the glaciers of the highest mountain in Mexico, the Pico de Orizaba, known as Citlatepetl in the local indigenous language. Like Swiss Water, it is non-chemical and relies on the fact that only 24-26% of coffee is soluble in water. The process works by soaking and immersing the green beans into this water. Looking for equilibrium, the caffeine and some soluble flavour molecules in the coffee beans begin to migrate out into the water solution. The water preserves the soluble flavour components of the green beans, helping to protect the original characteristics of the coffee. To separate and remove the caffeine from the water containing these soluble flavour elements, the water is passed through carbon filters. This traps the caffeine, allowing it to be removed, resulting in a solution comprising of the original mountain water and the soluble coffee flavours, now free from caffeine. The coffee beans are then reintroduced to this water, which allows the beans to reabsorb all the flavour molecules. This process is repeated continuously until the caffeine level is low. The resulting green coffee is 99.9% caffeine-free. The beans are then dried to the required moisture content, polished and packed, ready to export.
Swiss Water Decaffeination
Similarly, to the Mountain Water Process, a solution is created by soaking green coffee in water, allowing the soluble components in the coffee to leave the beans via the water. Using carbon filters, the caffeine is removed, the green beans are discarded, leaving a solution that is supersaturated with soluble coffee components, called a GCE (Green Coffee Extract). Green coffee to be decaffeinated is then immersed in this solution. The GCE flows over the green coffee beans and to find equilibrium, the caffeine in those coffee beans begins to migrate into the GCE. No other solubles migrate from the coffee beans, as Caffeine is the only substance preventing equilibrium and missing from the GCE solution. The GCE now contains caffeine but not for long, it flows through carbon filters that trap the caffeine molecules and is removed. This happens continuously for 10 hours, under finely controlled and monitored conditions, resulting in green coffee beans that are 99.9% caffeine-free and ready for roasting.
The CO2 process of decaffeination uses liquid Carbon Dioxide (CO2), a highly selective solvent for caffeine. The green coffee is soaked in water to open the bean’s “pores”, beginning the decaffeination process whereby caffeine molecules are able to move in and out of the beans. The coffee is then placed into a compression tower, where it is brought into contact with pressurized liquid CO2. The pressure transforms the CO2 into a supercritical state, where it is part liquid and part gas. By circulation through the coffee, the carbon dioxide bonds with the caffeine, drawing it out from the beans. The CO2 is then separated into an evaporator, where the caffeine precipitates from the CO2, which means the caffeine can be collected and used to resell. After this, the CO2 is pumped back into the vessel containing the green coffee for a new cycle. When the required caffeine level is reached, the CO2 circulation is stopped and the coffee is discharged into a drier where it is gently dried until it reaches the original moisture content. The coffee is then ready for roasting. This process can be quite expensive, as specialized equipment is required, but the Co2 is reused for later batches and the caffeine can be resold to other companies for energy drinks or Pharmaceuticals, keeping costs down.
Sugar Cane/ Ethyl Acetate Decaffeination
The final readily used decaffeination process is the Sugar cane, or Ethyl Acetate (EA), method. This method uses a naturally occurring compound, as sugar cane is fermented to become Ethyl Acetate. In this process the green coffee is steamed, causing the beans to swell, increasing the beans surface area. This opens the “pores” of the beans, ready for the molecules to move in and out. The beans are then soaked in an EA solution, which traps and dissolves the caffeine molecules. The coffee is next drained and steamed again to remove any traces of EA inside the beans. The EA is a selective compound, meaning it will bond with only the caffeine molecules in the bean, leaving the flavour molecules intact. This process is repeated until the required residual caffeine level is reached; the coffee is then ready for roasting. Like with the CO2 decaffeination method, the caffeine can usually be separated out from the drained EA solution, and resold, making the process less expensive as it provides a second stream of revenue.