Decaffeinated

Fig. 10. Semicontinuous coffee decaffeination process using supercritical CO2 (1).

Trichloroethylene was approved for use for many years as an extraction solvent for foods. In late 1977, the Eood and Dmg Administration (EDA) harmed its use as a food additive, direcdy or indirecdy, prohibiting the use in hop extraction, decaffeination of coffee, isolation of spice oleoresins, and other apphcations. The EDA also harmed the use of trichloroethylene in cosmetic and dmg products (23). 

Decaffeinated coffee products represented 18% of the coffee consumed in 1991 in the United States (31). Decaffeinated coffee was first developed commercially in Europe about 1900. The process as described in a 1908 patent (35) consists of first, moisturizing green coffee to at least 20% to facilitate transport of caffeine through the cell wall, and then contacting the moistened beans with solvents. 

In all the above mentioned processes of coffee decaffeination, changes occur that affect the roast flavor development. These changes are caused by the prewetting step, the effects of extended (four hours plus) exposure at elevated temperature as required to economically extract the caffeine from whole green beans, and the post-decaffeination drying step. 

To make an instant decaffeinated coffee product, the decaffeinated roast and ground coffee is extracted in a manner similar to nondecaffeinated coffee. Alternatively, the caffeine from the extract of untreated roasted coffee is removed by using the solvents described previously. 

Decaffeination Regulations. Eor decaffeinated roasted coffee, EEC standards indicate the maximum content of caffeine as 0.1% db for decaffeinated instant coffee it is 0.3% db. In the United States, decaffeination usually signifies that 97% of the caffeine has been removed. Permissible solvents for decaffeination processes are defined by national legislation, eg, EDA or EEC directive. The maximum residual solvent content after decaffeination, roasting, or instant coffee processing is to be kept within good manufacturing practice, ie, very low ppm levels or below at point of sale (46). 

FIG. 22-22 Schematic diagram of the Kraft process for producing decaffeinated coffee using supercritical carbon dioxide (McHugh and Ktukonis, op. cit.). 

In some cases, the solids themselves are subjected to extraction by a solvent. For example, in one process used to decaffeinate coffee, the coffee beans are mixed with activated charcoal and a high-pressure stream of supercritical carbon dioxide (carbon dioxide at high pressure and above its critical temperature) is passed over them at approximately 90°C. A supercritical solvent is a highly mobile fluid with a very low viscosity. The carbon dioxide removes the soluble caffeine preferentially without extracting the flavoring agents and evaporates without leaving a harmful residue. 

One of the most widely established processes using SCCO2 is the decaffeination of coffee. Prior to widespread use of this process in the 1980s the preferred extraction solvent was dichloromethane. The potential adverse health effects of chlorinated materials were realized at this time and, although there was no direct evidence of any adverse health effects being caused by any chlorinated residues in decaffeinated coffee there was always the risk, highlighted in some press scare stories. Hence the current processes offer health, environmental and economic advantages. 

Various consumer products have been found to contain trichloroethylene. These include wood stains, varnishes, and finishes lubricants adhesives typewriter correction fluids paint removers and cleaners (Frankenberry et al. 1987). Trichloroethylene use as an inhalation anesthetic, fumigant, and extractant for decaffeinating coffee has been discontinued in the United States (EPA 1985c). 

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. 

A French Standard, which corresponds to ISO 10095 issued in 1992, specifies a method for determination of caffeine in green or roasted coffee or in coffee extracts (decaffeinated or not).33 Caffeine is extracted with water at 90°C in the presence of MgO. The extract is filtered, then cleaned-up on a mini-column packed with a silica phenyl group derivative, and analyzed by HPLC on a C18 column with a methanol/water (30 70) mobile phase and a UV detector operating at 254 to 280 nm. 

A method for determining the caffeine content of regular and decaffinated green and roasted coffee beans and of regular and decaffeinated coffee extract powders, using HPLC, is specified in a British Standard Instruction.34 Caffeine is extracted from the sample with water at 90°C in the presence of magnesium oxide. The mixture is filtered and an aliquot purified on a silica microcolumn modified with phenyl groups. The caffeine content is then determined by HPLC with UV detection.35... 

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. 

Methylene chloride is probably the most generally used solvent for decaffeination processes, but others, some of which are already found in small amounts in coffee beans, are coming into use. For example, ethyl acetate,8 formaldehyde-dimethylacetal, ethanol, methanol, acetone,9 propane,10 benzyl alcohol,11 carbon dioxide,12 and supercritical carbon dioxide with an acid13 are used. Generally the pressure and temperature of the system are adjusted to keep the solvent in the liquid state. Coffee oil itself is even described for this use in one patent.14... 

In the U.S. the per capita consumption of coffee has declined by one-third since 1960. Parallel with this has been a change in the proportion of Robusta coffees imported into the U.S. In 1950 only 6% of the imported coffees were Robustas whereas by 1975, 35% were Robustas. In the 1950s, Robustas were mainly used for instant coffee now they also constitute a significant part of the roast and ground coffee blends. These Robustas are used to the highest extent in vending machines, restaurants, decaffeinated blends, and instant coffees. 

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. 

Peter, S. and Brunner, G., Decaffeinating coffee with solvents at high pressure, Ger. Offen. 2,737,794, 1979. (CA90 150500k)... 

Studiengesellschaft Kohle m.b.h, Decaffeinating coffee. Belg 856,955, 1978. (CA89 4866x)... 

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