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Decaffeination is the act of removing caffeine from coffee beans, cocoa, tea leaves and other caffeine-containing materials. (While caffeine-free soft drinks are occasionally referred to as "decaffeinated", some are better termed "uncaffeinated": prepared without adding caffeine during production.) Despite removal of most caffeine, many decaffeinated drinks still have around 1–2% of the original caffeine remaining in them, and research has found that certain decaffeinated coffee drinks can contain around 20% of the original caffeine.
In the case of coffee, various methods can be used. The process is usually performed on unroasted (green) beans, and starts with steaming of the beans. They are then rinsed with a solvent that extracts the caffeine while leaving the other essential chemicals in the coffee beans. The process is repeated anywhere from 8 to 12 times until it meets either the international standard of having removed 97% of the caffeine in the beans or the EU standard of having the beans 99.9% caffeine-free by mass. Coffee contains over 400 chemicals important to the taste and aroma of the final drink: It is, therefore, challenging to remove only caffeine while leaving the other chemicals at their original concentrations.
The first commercially successful decaffeination process was invented by Ludwig Roselius and co-workers in 1903 and patented a few years later. It involved steaming coffee beans with various acids or bases then using benzene as a solvent to remove the caffeine. Coffee decaffeinated this way was sold as Kaffee HAG after the company name Kaffee Handels-Aktien-Gesellschaft (Coffee Trading Company) in most of Europe, as Café Sanka in France and later as Sanka brand coffee in the U.S. Café HAG and Sanka are now worldwide brands of Kraft Foods. Due to health concerns regarding benzene, this process is no longer used commercially and Coffee Hag and Sanka are produced using a different process.
The use of water as the solvent to decaffeinate coffee was originally developed in Switzerland in the 1980s and is now used commercially under the trade-mark "Swiss Water Process" by The Swiss Water Decaffeinated Coffee Company of Burnaby, British Columbia, Canada. They describe it as a "chemical free" process.
Green coffee beans can be immersed in water to extract their caffeine but this will also extract desirable oils and other solids from the bean resulting in less flavourful brewed coffee. The Swiss Water process method attempts to overcome this difficulty by using water saturated with these desirable coffee components thus reducing or eliminating their extraction during the decaffeination process. Water saturated in this way is referred to as green coffee extract or GCE. It is created using a separate batch of green coffee beans that are immersed in water and then discarded. The GCE is then filtered to remove only the caffeine from it. A fresh batch of green coffee beans are then immersed in the GCE to remove caffeine but retain other components. The process of filtering the GCE to remove caffeine and immersing the beans is repeated until the beans are 99.9% caffeine free by mass. This process takes 8 to 10 hours.
In the direct method, the coffee beans are first steamed for 30 minutes and then repeatedly rinsed with either dichloromethane or ethyl acetate for about 10 hours. The solvent is then drained away and the beans steamed for an additional 10 hours to remove residual solvent. Sometimes coffees that are decaffeinated using ethyl acetate are referred to as naturally processed because ethyl acetate can be derived from various fruits or vegetables, but because of the impracticality of gathering natural ethyl acetate, the ethyl acetate used for decaffeination is synthetic.
In the indirect method, beans are first soaked in hot water for several hours, in essence making a strong pot of coffee. Then the beans are removed and either dichloromethane or ethyl acetate is used to extract the caffeine from the water. As in other methods, the caffeine can then be separated from the organic solvent by simple evaporation. The same water is recycled through this two-step process with new batches of beans. An equilibrium is reached after several cycles, wherein the water and the beans have a similar composition except for the caffeine. After this point, the caffeine is the only material removed from the beans, so no coffee strength or other flavorings are lost. Because water is used in the initial phase of this process, sometimes indirect method decaffeination is referred to as "water-processed" even though water is technically a chemical.
This process is technically known as supercritical fluid extraction. Pre-steamed beans are immersed in supercritical carbon dioxide in a pressure chamber at 73 to 300 atmospheres. After a thorough soaking for around ten hours, the pressurized CO2 containing dissolved caffeine is removed from the chamber which is returned to atmospheric pressure, allowing the CO2 to evaporate. The caffeine is removed from the CO2 using charcoal filters and the CO2 is recycled for use on another batch of beans. This process has the advantage that it avoids the use of potentially harmful substances.
Green coffee beans are soaked in a hot water/coffee solution to draw the caffeine to the surface of the beans. Next, the beans are transferred to another container and immersed in coffee oils that were obtained from spent coffee grounds.
After several hours of high temperatures, the triglycerides in the oils remove the caffeine — but not the flavor elements — from the beans. The beans are separated from the oils and dried. The caffeine is removed from the oils, which are reused to decaffeinate another batch of beans. This is a direct-contact method of decaffeination.
Tea may also be decaffeinated, usually by using processes analogous to the Direct Method or the CO2 process, as described above. Fermentation i.e., the process of oxidizing tea leaves to create black tea ("red" in Chinese tea culture) or oolong tea leaves from green leaves, does not affect the amount of caffeine in the tea, though tea-plant species (i.e., Camellia sinensis sinensis vs. Camellia sinensis assamica) may differ in natural caffeine content. Younger leaves and buds contain more caffeine per weight than older leaves and stems. Also, certain processes during production might lend a hand in either decreasing the caffeine content directly or simply lowering the rate at which it is released throughout each infusion. Several instances in China where this is evident is in many cooked pu-erh teas, as well as more heavily fired Wuyi Mountain oolongs; commonly referred to as 'zhonghuo' (mid-fired) or 'zuhuo' (high-fired). A generally accepted statistic is that a cup of black (red) tea contains 40–50 mg of caffeine, roughly half the content of a cup of coffee. Although a common technique of discarding a short (30– to 60-second) steep is believed to reduce caffeine content in a subsequent brew by 80–90%, research suggests that a five-minute steep yields up to 70% of the caffeine, and a second steep has one-third the caffeine of the first (about 23% of the total caffeine in the leaves).
A controlled study of ten samples of prepared decaffeinated coffee from coffee shops showed that some caffeine remained. Fourteen to twenty cups of such decaffeinated coffee would contain as much caffeine as one cup of regular coffee. The 16-ounce (473-ml) cups of coffee samples contained caffeine in the range of 8.6 mg to 13.9 mg. In another study of popular brands of decaf coffees, the caffeine content varied from 3 mg to 32 mg. A 8-ounce (237-ml) cup of regular coffee contains 95-200 mg of caffeine, and a 12-ounce (355-milliliter) serving of Coca-Cola contains 36 mg.
Both of these studies tested the caffeine content of store-brewed coffee, suggesting that the caffeine may be residual from the normal coffee served rather than poorly decaffeinated coffee.
|This section relies on references to primary sources. (October 2013)|
In women, consumption of decaffeinated coffee significantly decreases all-cause mortality with an odds ratio of between approximately 0.8 to 0.9 with a consumption of 1 cup to approximately 6 cups per day, compared to those who drink less than one cup per month. In men, these beneficial effects are not as great, yet show a tendency toward significantly less mortality for those that drink more than 2 cups per day compared to those that drink less than one cup per month.
As of 2009, progress toward growing coffee beans that do not contain caffeine was still continuing. The term "Decaffito" has been coined to describe this type of decaffeinated coffee, and trademarked in Brazil. The prospect for Decaffito type coffees was shown by the discovery of the naturally caffeine-free Coffea charrieriana, reported in 2004. It has a deficient caffeine synthase gene, leading it to accumulate theobromine instead of converting it to caffeine. Either this trait could be bred into other coffee plants by crossing them with C. charrieriana or an equivalent effect could be achieved by knocking out the gene for caffeine synthase in normal coffee plants.