Decaffeination of raw coffee by means of compressed nitrous oxide
Compressed gases are increasingly used as solvents in food processing. The applicability of these dense supercritical gases essentially depends on their solvent power. With respect to decaffeination the solubility of caffeine in nitrous oxide has been determined as a function of temperature and pressure. In nitrous oxide, saturated with water, about 600 ppm of caffeine is dissolved at 100 grade centigrade and 30 MPa. Most of the increase in solubility occurs in the pressure range from 10 to 20 MPa. On the basis of these results an investigation of the decaffeination of raw coffee was initiated, comprising the essential process steps of extraction and recovering the caffeine. For the experiments a commercially available apparatus with 4000 cm3 extraction volume was modified for our purposes. All the investigations were accompanied by sensorial tests. The solvent ratio (mass flow of gas/quantity of coffee beans) proved to be most important. High solvent ratios (in the range of 100) at the beginning of the extraction favour the decaffeination, while they are relatively ineffective during the second half of the decaffeination process. Since the diffusion of the caffeine in the coffee bean determines mass transport, an increasing solvent ratio results in a decreasing concentration of caffeine in the nitrous oxide solvent. The mean concentration of caffeine in the gas at constant solvent ratio proved independent on the ratio of height to diameter of the bed of coffee beans within a range of 0.6 < h/f < 3.1. As expected, decaffeination was accelerated by higher pressures and higher temperatures. The caffeine was recovered from the gas by absorption with water at a somewhat lower pressure than the extraction pressure
| Main Authors: | , , |
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| Format: | biblioteca |
| Published: |
París (Francia)
1988
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| Subjects: | CAFE, DESCAFEINIZACION, GASES SUPERCRITICOS, SOLVENTE, SEPARACION, CAFEINA, |
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