Decaffeination

Decaffeination is the removal of caffeine from coffee beans, cocoa, tea leaves, and other caffeine-containing materials. While soft drinks which do not use caffeine as an ingredient are sometimes described as "decaffeinated", they are better termed "non-caffeinated" because decaffeinated implies that there was caffeine present at one point in time. Decaffeinated drinks contain typically 1–2% of the original caffeine content, and sometimes as much as 20%.^[1] Decaffeinated products are commonly termed decaf.

History

Coffee

Friedlieb Ferdinand Runge performed the first isolation of pure caffeine from coffee beans in 1820. He did this after the poet Goethe requested he perform an analysis on coffee beans after seeing his work on belladonna extract.^[2] Though Runge was able to isolate the compound, he did not learn much about the chemistry of caffeine itself, nor did he seek to use the process commercially to produce decaffeinated coffee.

The first commercially successful decaffeination process was invented by German merchant Ludwig Roselius and co-workers in 1903 and patented in 1906.^[3][4] In 1903, Ludwig accidentally stumbled upon this method when his freight of coffee beans was soaked in sea water and lost much of its caffeine without losing much taste.^[5] This original decaffeination process involved steaming coffee beans with various acids or bases, then using benzene as a solvent to remove the caffeine.^[6] 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. Because of health concerns regarding benzene (which is recognised today as a carcinogen^[7]), benzene is no longer used as a solvent commercially.

Since its inception, methods of decaffeination similar to those first developed by Roselius have continued to dominate. While Roselius used benzene, many different solvents have since been tried after learning of the potential harmful effects of benzene. The most prevalent solvents used to date are dichloromethane and ethylacetate.^[8]

Another variation of Roselius' method is the indirect organic solvent method. This is very similar to the process described above, only instead of treating the beans directly, water resulting from the soaking of beans is treated with solvents and the process goes on until equilibrium is reached without caffeine in the beans. This method was first mentioned in 1941, and people have made great efforts to make the process more "natural" and a true water-based process by finding ways to process the caffeine out of the water in ways that circumvents the use of organic solvents.^[9]

Another process, known as the Swiss Water Method, uses solely water and osmosis to decaffeinate beans. The use of water as the solvent to decaffeinate coffee was originally pioneered in Switzerland in 1933 and developed as a commercially viable method of decaffeination by Coffex S.A. in 1980.^[3] In 1988, the Swiss Water Method was introduced by The Swiss Water Decaffeinated Coffee Company of Burnaby, British Columbia, Canada.^[10] Noted food engineer Torunn Atteraas Garin also developed a process to remove caffeine from coffee.^[11]

Most recently, food scientists have turned to supercritical carbon dioxide as a means of decaffeination. Developed by Kurt Zosel, a scientist of the Max Planck Institute, it uses CO₂, heated and pressurized above its critical point, to extract caffeine^[3] and could be useful going forward because it circumvents the use of other solvents and their possible effects entirely.

Decaffeination processes for coffee

In the case of coffee, various methods can be used. The process is 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 other constituents largely unaffected. The process is repeated from 8 to 12 times until the caffeine content meets the required standard (97% of caffeine removed according to the US standard, or 99.9% caffeine-free by mass per the EU standard).

Common characteristics of decaffeination

In all decaffeination processes, coffee is always decaffeinated in its green, unroasted state. The greatest challenge to the decaffeination process is to try to separate only the caffeine from the coffee beans while leaving the other chemicals such as sucrose, cellulose, proteins, citric acid, tartaric acid, and formic acid at their original concentrations. This is not an easy task considering coffee contains somewhere around 1,000 chemicals that contribute to the taste and aroma.^[3] Since caffeine is a polar, water-soluble substance, water is used in all forms of decaffeination. However, water alone is not the best solution for decaffeination because it is not a selective solvent and therefore removes other soluble substances, including sugars and proteins, as well as caffeine. Therefore, most decaffeination processes use a decaffeinating agent such as methylene chloride, activated charcoal, CO₂, or ethyl acetate.^[3] These agents help speed up the process and minimize the “washed-out” effects that water alone might have on the taste of decaffeinated coffee.^[3]

Swiss Water process

The Swiss Water® Process does not directly or indirectly add chemicals to extract caffeine. Rather, it relies entirely on two concepts – solubility and osmosis – to decaffeinate coffee beans.^[3]

The Swiss Water® Process uses Green Coffee Extract (GCE) for the caffeine extraction mechanism.  Green Coffee Extract is a solution containing the water-soluble solids components of green coffee except the caffeine.  The process relies on the stability of the soluble components of the GCE and the gradient pressure difference between the GCE (which is caffeine lean) and the green coffee (which is caffeine rich). This gradient pressure causes the caffeine molecules to migrate from the green coffee into the GCE.^[3] Because GCE is saturated with the other water-soluble components of green coffee only the caffeine molecule migrates to the GCE; the other water-soluble coffee elements are retained in the Green Coffee. This is what makes the GCE caffeine selective and specific.

Once the GCE is rich with caffeine it is then percolated through carbon absorbers which attract the caffeine molecule from the GCE while leaving other green coffee elements intact in the GCE. When the GCE is once again lean of caffeine it is then used to remove additional caffeine from the green coffee. This is a continuous batch process that take 8-10 hours to meet the final residual decaffeinated target, which is 99.9% caffeine free by mass.^[12][13]

Organic solvent processes

Solvents used in decaffeination

Given numerous health scares connected to early efforts in decaffeination^[12] using solvents such as benzene, trichloroethylene, and chloroform, the solvents of choice have become dichloromethane and ethyl acetate.^[3] Dichloromethane is able to extract the caffeine selectively and has a low boiling point. Although it is mildly toxic and carcinogenic,^[13] its use as a decaffeination agent is allowed by the US Food and Drug Administration if the residual solvent is less than 10 parts per million (ppm).^[14] Actual coffee industry practice results in residues closer to one part per million.^[3] Starting in the 1980s, ethyl acetate was introduced as a replacement to dichloromethane.^[15] Although ethyl acetate is mildly toxic,^[16] coffee that is decaffeinated with this solvent is sometimes marketed as "naturally decaffeinated" because this solvent may be obtained from a biological process such as the fermentation of sugar cane.^[17]

Direct method

In the direct method, the coffee beans are first steamed for 30 minutes to open their pores and then repeatedly rinsed with either dichloromethane or ethyl acetate for about 10 hours to remove the caffeine. The caffeine-laden solvent is then drained away and the beans steamed to remove residual solvent.^[18]

Indirect method

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.^[19] Because water is used in the initial phase of this process, indirect method decaffeination is sometimes referred to as "water-processed".

CO₂ process

This process has been referred to as CO₂ Method, Liquid Carbon Dioxide Method, and Supercritical Carbon Dioxide method but it is technically known as supercritical fluid extraction.

The supercritical CO₂ acts selectively on the caffeine, releasing the alkaloid and nothing else. Water-soaked coffee beans are placed in an extraction vessel. The extractor is then sealed and supercritical CO₂ is forced into the coffee at pressures of 1,000 pounds per square inch (about 69 bar) to extract the caffeine.^[3] The CO₂ acts as the solvent to dissolve and draw the caffeine from the coffee beans, leaving the larger-molecule flavor components behind. The caffeine-laden CO₂ is then transferred to another container called the absorption chamber where the pressure is released and the CO₂ returns to its gaseous state and evaporates, leaving the caffeine behind.^[3] The caffeine is removed from the CO₂ using charcoal filters, and the caffeine free CO₂ is pumped back into a pressurized container for reuse on another batch of beans. This process has the advantage that it avoids the use of potentially harmful substances. Because of its cost, this process is primarily used to decaffeinate large quantities of commercial-grade, less-exotic coffee found in grocery stores.^[3]

Triglyceride process

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 and left to soak.

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.

Decaffeinated coffee

Caffeine content of coffee

Caffeine content of decaffeinated coffee

To ensure product quality, manufacturers are required to test the newly decaffeinated coffee beans to make sure that caffeine concentration is relatively low (no less than 97% caffeine content reduction according to United States standards).^[20] To do so, many coffee companies choose to employ High-performance liquid chromatography to quantitatively measure how much caffeine remains in the coffee beans. However, since HPLC can be quite costly, some coffee companies are beginning to use other methods such as Near-infrared (NIR) spectroscopy.^[21] Although HPLC is highly accurate, NIR spectroscopy is much faster, cheaper and overall easier to use. Lastly, another method typically used to quantify remaining caffeine includes Ultraviolet–visible spectroscopy, which can be greatly advantageous for decaffeination processes that include supercritical CO_2, as CO₂ does not absorb in the UV-Vis range.^[22]

A controlled study of ten samples of prepared decaffeinated coffee from coffee shops showed that some caffeine remained.^[1] Fourteen to twenty cups of such decaffeinated coffee would contain as much caffeine as one cup of regular coffee.^[1] 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.^[23] An 8-ounce (237-ml) cup of regular coffee contains 95–200 mg of caffeine,^[24] and a 12-ounce (355-milliliter) serving of Coca-Cola contains 36 mg.^[25]

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.

Decaffito

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.^[26]

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.^[27] 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.^[28]

Decaffeinated tea

Tea may also be decaffeinated, usually by using processes analogous to the direct method or the CO₂ process, as described above. 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. Although the CO₂ process is favorable because it is convenient, nonexplosive, and nontoxic,^[29] a comparison between regular and decaffeinated green teas using supercritical carbon dioxide showed that most volatile, nonpolar compounds (such as linalool and phenylacetaldehyde), green and floral flavor compounds (such as hexanal and (E)-2-hexenal), and some unknown compounds disappeared or decreased after decaffeination.^[30]

In addition to CO₂ process extraction, tea may be also decaffeinated using a hot water treatment. Optimal conditions are met by controlling water temperature, extraction time, and ratio of leaf to water, where higher temperatures at or over 100 °C, moderate extraction time of 3 minutes, and a 1:20 water to leaf weight per volume ratio removed 83% caffeine content and preserved 95% of total catechins.^[31] Catechins, a type of flavanol, contribute to the flavor of the tea and also, interestingly, have been shown to increase suppression of mutagens that may lead to cancer.^[32]

Both coffee and tea have tannins, which is responsible for the astringent taste, but tea has nearly three times smaller tannin content than coffee.^[33] Thus, decaffeination of tea requires more care to maintain tannin content than decaffeination of coffee in order to preserve this flavor. Preserving tannins is desirable not only because of their flavor, but also because they have been shown to have anticarcinogenic, antimutagenic, antioxidative, and antimicrobrial properties. Specifically, tannins accelerate blood clotting, reduce blood pressure, decrease the serum lipid level, produce liver necrosis, and modulate immunoresponses.^[34]

Certain processes during normal production might help to decrease the caffeine content directly, or simply lower 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 normal black (often called red in China; as distinct from green) tea contains 40–50 mg of caffeine, roughly half the content of a cup of coffee.^[35]

Although a common technique of discarding a short (30- to 60-second) steep^[36] is believed to much reduce caffeine content of a subsequent brew at the cost of some loss of flavor, 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).^[37]

See also

• Health effects of caffeine
• Health effects of coffee
• Health effects of tea
• Coffee substitute

References

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