INTRODUCTION
The major pharmacologically active ingredient in coffee is caffeine, chemically known as1,3,7-trimethylxanthine. Caffeine occurs naturally in some 60 plant species, of which cocoa-beans, tea and coffee are the most well known. Caffeine is added to many popular carbonated drinks, and is a component of a number of pharmacological preparations and over-the-counter medication including analgesics (where caffeine assists the pain relieving effect), diet aids, and cold/flu remedies.
The effects of caffeine have been the subject of considerable discussion and research, due in no small part to the popularity of coffee which is acknowledged as being one of the worlds favourite drinks. Thousands of scientific studies have been published on the effects of coffee and caffeine on health, the overall conclusion of which confirms that coffee drinking in moderation, 4-5 cups per day, is perfectly safe for the general population and may confer health benefits. However, some individuals may choose to consume decaffeinated coffee, tea, or soft drinks, especially later in the day.
DECAFFEINATED COFFEE
Decaffeinated coffee is coffee which has had almost all of the caffeine removed. Commercial decaffeination processes were started in Germany during the early part of the 20th century. There are different methods of decaffeination, though the end result is more or less the same. All methods safely and selectively remove the caffeine leaving a maximum of 0.3% in soluble coffee and 0.1% in roast & ground coffee.
There are four methods used – Water, Ethyl Acetate, Methylene Chloride and Supercritical or liquid Carbon Dioxide. All methods are subject to legislation and all achieve good results for both instant and roast & ground coffee. 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 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 fruits. 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 to extract 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 breathe 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, where 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 dichloromethane is circulated around the water soaked beans to extract 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 guarantees that possible solvent residues remain below the limits fixed by European legislation.
SUMMARY
Some people choose to drink decaffeinated coffee. Caffeine is a mild stimulant, and some people who drink coffee do not always want the mild stimulatory effects. Many consumers drink both caffeinated and decaffeinated coffee, depending on their mood or time of day.