Decaffeinated Coffee
From Chempedia
Authors
Nicole Longville
Ryan Schumacher
Ashish Sharma
Chem. 1022
Nov 11, 2005
Decaffeinated Coffee
During the early part of the 20th century, the process of decaffeinating coffee was hit upon by Germans scientists (2). The concept behind decaffeinated coffee is quite simple. As the name implies, decaffeinated coffee is coffee with at least 97% of all the caffeine removed (5). In a five-ounce cup of decaffeinated coffee, there is roughly five milligrams of caffeine compared to 70 to 155 milligrams found in a regular cup (5). The chemistry behind decaffeination is also quite elegantly simple, revolving around three main processes: water decaffeination, carbon dioxide decaffeination, and solvent decaffeination. All of the processes start with the same step, which is to steam or soak the green coffee beans in water. The green coffee beans are the initial state before the beans are roasted, which is responsible for the aroma. All of these processes merely employ different methods of removing the caffeine and are quite similar, though each has their own benefits and drawbacks as will be seen (6).
Figure 1: The Caffeine molecule.
Water decaffeination, also known as the Swiss Water Process, uses no chemicals (1). The green beans, which are the natural appearance of coffee beans, are soaked in hot water, removing the caffeine and the majority of the flavor present in each bean. The aqueous solution that is formed is then passed through an activated carbon filter which separates the caffeine from the solution without removing the flavors. The beans are then re-soaked in this flavor-saturated solution (5). Since caffeine is water-soluble, the caffeine simply moves from the high concentration in the beans to the low concentration of the aqueous solution (1). Lastly, the solution is passed through the active carbon filter; the porous charcoal of the filter traps the impurities, in this case, caffeine (7).
In the carbon dioxide process, the pre-wetted green coffee beans come into contact with supercritical or liquid carbon dioxide. The caffeine is first removed by the carbon dioxide, and then caffeine is scrubbed from the carbon dioxide using activated carbon filters. The carbon dioxide is finally recycled and used to extract more caffeine from other batches of green coffee beans (4). Carbon dioxide is non-toxic and inexpensive, so the dry, roasted and ready-to-brew decaffeinated coffee beans of the carbon dioxide process are more appealing and less expensive to consumers.
Figure 2: Decaffeination by Carbon Dioxide (4)
The solvent decaffeination process typically makes use of methylene chloride or ethyl acetate to remove the caffeine molecule (C8H10N4O2) from coffee. Methylene Chloride (dichloromethane CH2Cl2) is a chemical compound used as a solvent for organic materials. First prepared in 1840 by French Chemist Henri Victor Regnault, it has a wide range of uses including as being used as a: paint stripper, a degreaser, an extractor of hops, and much more (9).
Methylene chloride is used as a solvent to extract caffeine because molecules of caffeine bond to the molecules of methylene chloride. The beans are softened in steam or in a water bath. The next step is to process the beans with methylene chloride by one of two methods.
In the first method, the caffeine is removed by directly soaking the materials in methylene chloride. In the second method, the methylene chloride is used indirectly by first soaking the green beans in hot water, similar to the Swiss Water Process, extracting the oils, flavors, and the caffeine. The solution is then treated with methylene chloride before the decaffeinated solutions is returned to the beans to allow for re-absorption of the flavors. Unfortunately, there is a draw back to both methods. Methylene chloride is toxic (3).
While methylene chloride is the least toxic of the simple chlorohydrocarbons, there still are safety concerns when used in large quantities. Chronic exposure to this solvent may be carcinogenic, and can cause birth defects if women are exposed during pregnancy. In many countries products containing methylene chloride must carry labels warning of its health risks. The Food and Drug Administration allows the use of methylene chloride because is lingering presence is about 100 times below the concentration deemed safe (3).
The use of ethyl acetate in the decaffeination process is the same as to methylene chloride; ethyl acetate is used as the solvent instead (3). This process is usually referred to as natural decaffeination because ethyl acetate is a chemical that occurs naturally in many fruits.
Ethyl acetate (CH3COOCH2CH3), which is an ester, is synthesized from acetic acid and ethanol in the presence of strong acids in the reaction:
CH3CH2OH + CH3COOH -> CH3COOCH2CH3+H2O.
Because the reaction favors the reactants in equilibrium, the yield of ethyl acetate is low unless driven to the right by the extracting water. Other uses of ethyl acetate are as a poison used for insect collection, a solvent in glues and nail polish removers, chemical reactions, and extractions (8).
In the end, the biggest concern of decaffeinated coffee is deciding what process provides the most enjoyable cup for the consumer. All of the processes discussed have little to no adverse effects on the consumer’s health, even when industrial chemicals such as methylene chloride are used to prepare the coffee. If anything, consumers are injecting fewer chemicals into their bodies by drinking the decaffeinated coffee. So whether you prefer the Swiss Water Process, or the use of a chemical solvent, the most important aspect you have to pay attention to is which one fits your tastes best.
Bibliography
1."Decaffeination." Coffeeresearch.org. Coffee Research Institute. October 16, 2005. [1].
2. "The Coffee Decaffeination Processes." Leda. 9/5/2001. The [Lycaeum Entheogen Database-http://leda.lycaeum.org/]. October 16, 2005. [2].=
3. "Decaffeination Methods." BaristaGuru. Barista Guru LLC. October 16, 2005. [3].
4. "Decaffeinated Coffee." Greener Industry. Chemical Industry Education Centre October 16, 2005. [4].
5. "Swiss Water Process." Chilipaper.com. [The RHCP Group-mailto:rhcp@chilipaper.com]. October 16, 2005. [5].
6. Jacobs, Ryan. "Caffeine and The Bean." INeedCoffee. Digital Colony. October 16, 2005. http://www.ineedcoffee.com/99/06/decaf.==
7. "What is activated charcoal and why is it used in filters? What is activated charcoal and why is it used in filters?" Howstuffworks.com. HSW Media Network. October 26, 2005. [6].
8. "Ethyl Acetate" Occupational Safety and Health Administration. United States Department of Labor. October 29, 2005. http://www.osha.gov/SLTC/healthguidelines/ethylacetate/recognition.html.
9. "Methylene Chloride." Environmental Health & Safety. Mallinckrodt Baker, Inc. October 29, 2005. http://www.jtbaker.com/msds/englishhtml/M4420.htm.
