Coffee is consumed in large amount by populations across the world and is the world’s second most valuable commodity after petroleum. Coffee has now been available in the decaffeinated form for decades.
In the past, the methylene chloride extraction process was used to decaffeinate coffee. Methylene chloride was continuously circulated through the coffee beans to extract the caffeine, which would usually take 24 to 36 hours. The solvent then needed to be stripped from the coffee beans, which would take another 1 to 8 hours. Decaffeination therefore used to be a long and tedious process. The process is also toxic as it often leaves a residue of the solvent on the beans. More recent methods of decaffeination tend to be faster to perform as well as not leaving any toxic residue.
Caffeine side effects
The stimulatory effects of caffeine may begin as early as 15 minutes after ingesting the drug and last for as long as six hours. In moderate doses, caffeine helps to increase alertness and reduces sleepiness and does not usually have long-term side effects.
However, regular ingestion of excess amounts of caffeine can lead to problems such as poor concentration, nervousness, heartburn, constipation and diarrhea. Longer-term effects include sleep deprivation, impaired judgement, emotional fatigue, mood swings, depression and anxiety.
One serving of coffee usually contains around 40 mg of caffeine in a single 30 ml shot. Drip coffee contains around 100 mg in a 120 ml cup of coffee. Arabica coffee normally contains less caffeine than the robusta variety. In general, dark-roast coffee has less caffeine than lighter roasts because roasting reduces the caffeine content.
According to the Food and Drugs Administration, coffee must have 97% of the caffeine removed for it to qualify as decaffeinated. The processes involved in decaffeination are described below.
Decaffeination by hot water
Hot water can be used to extract caffeine from green coffee beans, but the process also involves extracting the flavor. Passing the extract over activated charcoal removes most of the caffeine and the original caffeine beans are then soaked in the decaffeinated extract to restore the flavor that was lost.
Swiss Water process
In the 1980s, the Swiss developed a way of decaffeinating coffee that doesn’t remove the coffee’s flavor in the first place. The “Swiss Water process” involves using caffeine-free water charged with flavor to extract the caffeine from the green coffee beans. As the water is already filled with flavours, only caffeine moves out of the beans and into the water.
Supercritical fluid CO2 extraction
If a sealed compartment containing both gaseous and liquid carbon dioxide under high pressure is heated, the liquid density drops while the gas density rises. If the temperature is raised to over 304.2 K, the liquid and gas densities become identical. Here, the carbon dioxide becomes a supercritical fluid with both gas-like and liquid-like properties. The supercritical fluid extracts the caffeine by forcing it through the green coffee beans. The fluid’s gas-like behavior allows it to penetrate deep into the beans and remove 97% to 99% of the caffeine in them.
This caffeine is recovered from the process by techniques including charcoal adsorption, distillation, recrystallization, or reverse osmosis and used in other products such as soft drinks, energy drinks and medicines.
Reviewed by Sally Robertson, BSc