Proposed modifications to the basic coffee extraction schemes

3 Proposed modifications to the basic coffee extraction schemes 

2 Liquid CO2 as extractant. A second modification to the processes described in section 5.4.2 which has been proposed is to use liquid, rather than supercritical, CO2 as the extractant. By operating at pressures not substantially in excess of the vapour pressure, substantially lower pressures can be used than in the supercritical case, though the caffeine solubilities are also lower. As pointed out in chapter 10, this will result in a higher solvent throughput for a given amount of product. A process of this type is described in European 

Patent Application 0316694 (24.05.1989). Extraction temperatures between 20 and 25°C and pressures between 65 and 70 bar are proposed. An economic analysis is required to establish whether the additional costs associated with the large throughputs of solvent in this process are offset adequately by the cost advantages of working at a lower pressure. In addition to the above, a process has been described in which liquid CO2 is used at a pressure above the critical pressure [32]. 

Further entrainer-based processes are described in US Patents 4,255,458 [35] and 4,472,442 (18.09.1984). In the latter case the entrainer is dimethyl sulfoxide and adsorption is used to separate the caffeine from the extraction medium. 

All the entrainer-based processes suffer from the disadvantage that it is necessary to strip the entrainer from the coffee beans after extraction. 

---