Decaffeination of Green Coffee Beans

Some Applications of Supercritical Extraction of Solids 8.2.14.1 Decaffeination of Green Coffee Beans 

Variations of the above-described process use activated charcoal instead of the column for the removal of caffeine. The adsorbent is placed either in a separate vessel or mixed with the coffee beans and placed within the extractor. Depending on the type of coffee, the extraction time is between 6 h and 8 h and about 1 kg of activated charcoal is needed for 3 kg of coffee beans. Recovery of caffeine is not possible, but reactivation of charcoal at 600 °C is possible with about 30% of loss. 

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Decaffeination of green coffee beans is most usually carried out with a water/solvent partition system. The green coffee beans are first steamed until they are hot, wet, and swollen, to make the caffeine available. Solvent is then used to extract the caffeine out of the aqueous phase of the beans. Finally, the beans are steamed to drive off residual solvent. The coffee beans lose their wax surface covering in the process, as well as some flavor components. For this reason, the Robusta and Brazilian Arabica coffees that are dry-processed and have the most powerful flavors are usually the types that are decaffeinated. They become milder in the process. Mechanical polishing is used to improve the appearance of decaffeinated green coffee beans if they are not to be roasted immediately. Extra care is required, however, to store these decaffeinated beans since the loss of wax covering as well as caffeine renders them much more susceptible to fungal attack. 

Methods for the decaffeination of green coffee beans, mainly with solvents after a steaming, have already been described. Even with the selective adsorption techniques to remove only caffeine, it is unlikely that the full character of the starting beans can be realized in a final decaffeinated beverage the result is that Robusta coffees are generally used to prepare decaffeinated coffee. The cost is kept down and the treatment, anyway, reduces any harsh or bitter flavor that the Robusta coffee may have had. The resulting beverage will be relatively caffeine-free, but Robusta coffee will contribute more soluble carbohydrates, phenols, and volatile fatty acids, and much less of the diterpenes found in Arabica coffees. 

As one of the first processes, the decaffeination of green coffee beans was applied on the industrial scale [6]. Zosel proposed three possibilities for the decaffeination. In the first, the moistened green coffee beans are extracted in a pressure vessel at 160 to 220 bar. The caffeine diffuses from the beans into the C02, which is fed into the washing-tower [8],... 

Figure 9.6-1. Zosel s suggestion for the decaffeination of green coffee beans [8]...

Figure 5 1 Zosel s first process for the decaffeination of green coffee beans with supercritical CO2. (Operating conditions are 90°C, 160-200 atm, carbon dioxide density in range 0.4-0.65 g cm ). In this process the caffeine is removed from the CO2 by washing with water. Reproduced with permission from K. Zosel (see caption to Figure 5.3).

Zosel [3] described in 1980 different possibilities for the decaffeination of green coffee beans, a process that was the first to be applied on large industrial scale. The isobaric process (Figure 8.10) operates at pressures 160 bar-220 bar, using a countercurrent column for caffeine separation by means of demineralized water at temperatures between 70 °C and 90 °C. Depending on caffeine concentration, 31-51 of water per kilogram of coffee is required. 

Since the first large-scale supercritical extraction process was commercialized for the decaffeination of green coffee with carbon dioxide a decade ago, scientists and engineers in the food industry have been paying considerable attention to this technique for similar separations, i.e., removal of cholesterol from butter, removal of cocoa butter from cocoa beans, and extraction of hops, spices, and... 

As in the case of green coffee beans, the presently used commercial methods for decaffeination of green tea leaves have been liquid solvent extraction, using chlorinated solvents, ethyl aeetate, acetone, ethanol and acetonitrile. Although good decaffeination can be achieved using these solvents, catechins are also considerably co-extracted and thus, the value of green tea as a functional healthy drink is reduced. 

Decaffeination of Coffee and Tea This application is driven by the environmental acceptability and nontoxicity of CO2 as well as by the ability to tailor the extraction with the adjustable solvent strength. It has been practiced industrially for more than two decades. Caffeine may be extracted from green coffee beans, and the aroma is developed later by roasting. Various methods have been proposed for recovery of the caffeine, including washing with water and adsorption. 

In the third variation a mixture of moisturized green coffee beans and activated carbon is filled into the extractor, and the activated carbon pellets used are just big enough to fit between the beans. For 3 kg of coffee beans, 1 kg of activated carbon is needed. At 220 bar and 90°C the caffeine in the supercritical CO2 diffuses directly out of the beans into the activated carbon. A CO2 circulation is not necessary. The required degree of decaffeination is reached after 6 to 8 hours. After extraction, the beans and activated carbon are separated by a vibrating sieve. 

Caffeine is a naturally occurring substance found in the leaves, seeds, or fruits of more than 60 plants. These include coffee and cocoa beans, kola nuts, tea leaves, guarana (Paulinia cupana) and Paraguay tea. Thus it is present naturally in many beverages, such as coffee, tea, and cola drinks, or is added in small amounts (up to 200 ppm) in some soft drinks and in foods such as chocolate. Caffeine is obtained by solvent or supercritical fluid extraction from green coffee beans, mainly during the preparation of decaffeinated coffee. 

Food and Pharmaceutical Applications These applications are driven by the environmental acceptability of CO2, as well as by the ability to tailor the extraction with the adjustable solvent strength. The General Foods coffee decaffeination plant in Houston, Texas is designed to process between 15,000 and 30,000 pounds of coffee beans per hour (McHugh and Kmkonis, op. cit.). See Fig. 22-22. The moist, green coffee beans are charged to an extraction vessel approximately 7 ft diameter by 70 ft high, and carbon dioxide is used to... 

Consider the chemistry required to decaffeinate coffee. Most techniques use an extraction process to remove the caffeine from the green coffee beans before they are roasted. One method starts by steaming the green beans and then rinsing them with an organic solvent (usually dichloromethane) to pull the caffeine molecules out of the beans. The other method uses supercritical carbon dioxide to extract caffeine. The latter obviously avoids the use of toxic solvents, but is energy-intensive. With all extraction techniques,... 

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