Decaffeinating of coffee beans

The particle-size distribution and the shape of the particles also influence the ratio of length-to-diameter of the extractor. As the costs for extractors depend not only on volume, but mainly on the diameter, the proper selection of the extractor height/diameter ratio must be made, with a preference for slim vessels. So far, only for the decaffeination of coffee beans with a particle size of about 7 mm can large ratios of 9 1 (length to diameter) be applied. For large particle sizes it is of advantage to feed the solvent from top to bottom, in order to avoid back-mixing. For the usual particle-size-distribution, ratios of 6 1 should be used. For raw material which tends to swell, like black tea or paprika, the ratio should be only 3 1, or if the extractor is equipped with baskets, the baskets should be equipped with multiple distribution. 

PROBLEM 3.10 Dichloromethane (CH2C12), sometimes used as a solvent in the decaffeination of coffee beans, is prepared by reaction of methane (CH4) with chlorine. How many grams of dichloromethane result from reaction of 1.85 kg of methane if the yield is 43.1% ... 

A significant development in supercritical fluid extraction was Zosel s patent for decaffeination between 1964 and 1981, which reported a procedure for the decaffeination of coffee beans with C02 [6-10]. Also, a number of patents of some food companies have been reported that concern the decaffeination of coffee [11]. The American Food Company, for example, has constructed an extraction vessel 7 ft in diameter and 70 ft tall for supercritical C02 decaffeination of coffee at the Houston, Texas plant. The current annual U.S. market for decaffeinated coffee is 2- 3 billion [4]. 

Due to its unique characteristics and physicochemical properties such as being less toxic, nonflammable, and having the extraction power tuned by temperamre and pressure, SC CO2 can be used as a green solvent for extraction of substances especially from solid or liquid substrates. Such extraction has been carried out on commercial scale for more than two decades and applications like decaffeination of coffee beans and black tea leaves and hops extraction are involved in large-scale processes [17]. Other extractions such as extraction of flavors, spices, and essential oils from plant materials are under investigation. An overview of published data for different materials is given in the review of Marr and Gamse [18]. 

The lowering of pressure to precipitate the extract is not always necessary. For example, in the case of decaffeination of coffee beans, water can be used to extract caffeine from the COi/caffeine mixture, as caffeine is readily soluble in water (Fig. 3). 

Fig. 3 Decaffeination of coffee beans using supercritical fluid extraction.

The use of critical fluids for the extraction and refining of components in natural products has now been facilitated for over 30 years. Early success in the decaffeination of coffee beans and isolation of specific fractions from hops for flavoring beer, using either supercritical carbon or liquid carbon dioxide, are but two examples of the commercial application of this versatile technology. Critical fluid technology, a term that will be used here to embrace an array of fluids under pressure, has seen new and varied applications which include the areas of engineering-scale processing, analytical, and materials modification. 

Figure 1 Simpiified flow scheme for decaffeinating of coffee beans by SCCO2.

The oldest commercially used SCCO2 extraction process is the decaffeination of coffee beans. This is still the most profitable application of SCCO2, but supercritical fluids have been tested in the food industry, pharmaceutical industry, textile dyeing, impregnation, polymer synthesis and processing, dry cleaning, etc. ... 

The viability of continuous extraction depends on the availability of lock systems which will enable solid material to be injected into the high pressure extractor and then removed from it without incurring unacceptable loss of solvent. These systems have been discussed by Reimert [24]. (It should be remembered that some solvent will normally be present in voids within the bed of extracted material.) The author finds it useful to classify lock systems into form preserving systems (required for example in the decaffeination of coffee beans), form-changing systems (which could be used, for example for de-oiling seeds or the extraction of the bitter components from hops) and systems in which a solid to be processed is injected into the extraction zone as a suspension in a suitable fluid. This classification applies irrespective of whether the solid is being conveyed into or out of the pressure chamber and is shown in Table 8.5. 

The most successful application of ScCO is the decaffeination of coffee beans [55], The main reason for its sueeess is the saving in energy costs, as caffeine ean be removed from eompressed CO without release of pressure, by extraetion with water. ScCO separation is used in food industry for other proeesses too as CO is nontoxie. 

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