Decaffeinated coffee

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1. General Flowsheet of decaffeinated coffee production

Flowsheet of decaffeinated coffee production, figure1.jpg

Figure 1: Flowsheet of decaffeinated coffee production Literature: Ullmann's Encyclopedia of Industrial Chemistry, Vol.A7, 1994

2. Description of techniques, methods and equipment
(Ullmann's Encyclopedia of Industrial Chemistry, Vol.A7, 1994)

The stimulating effect of coffee is due to the presence of alkaloid caffeine. Decaffeinated coffee gives a brew devoid of this effect. The presence of water is essential in decaffeination to soften and open the cellular structure of the beans and to ensure the diffusion of caffeine across the cell walls by solubilizing the caffeine-potasium chlorogenate complex. Industrial processes, which are usually carried out with green beans, can be broadly divided into two types: those performed at moisture levels below 50% (usually between 30-45%), and those performed above 50% (usually between 55-65%).

(a) Low-moisture processes: Low moisture decaffeination processes are applied to green coffee to avoid removing or altering fragile aromatic constituents formed during roasting. The beans are soaked in a mixer column or rotating drum and extracted with a non-polar solvent in one or more columns or rotating drums. The residual caffeine level in the beans is lowered to less than 0.1% in the dried decaffeinated beans by most national regulations, or to less than 3% of the amount initially present (the commercial practice in some countries). The beans are then deodorized (solvent traces are removed by steam stripping) and dried to their initial moisture content in a tower or a fluidized bed drier under atmospheric or reduced pressure. The solvent is recovered by batch or continuous evaporation, or by steam stripping of the caffeine under vacuum. Losses due to leaching of hydrosoluble material are low, and caffeine, containing a few percent of waxes from the surface of the beans, is recovered and purified by successive crystallizations to pharmaceutical grade for use in soft drinks and medicines.

(b) High-moisture processes: In high-moisture processes, green or roasted coffee beans are soaked in water until they have reached the required moisture level. Decaffeination is carried out by dissolution with an aqueous solution of 10-30% non-caffeinic, soluble coffee solids. The resulting caffeine-enriched solution is then decaffeinated either by liquid-liquid extraction with any of the solvents used in the low-moisture processes or by adsorption of the caffeine on activated carbon or on ion-exchange resin. This solution is then used to decaffeinate new beans. Alternatively, the swollen green beans may be decaffeinated with fresh water. After removal of the caffeine the solution is concentrated and reabsorbed on the pre-dried decaffeinated beans from which it has been obtained, thus replacing non-caffeine solids otherwise lost.

(c) Processes using supercritical media: Supercritical carbon dioxide, i.e., at temperatures and pressures above the critical point of 31.06°C and 73.8bar can be used to decaffeinate coffee by a process called destraction. The supercritical medium in a pressured vessel is circulated through moist coffee, where it becomes charged with caffeine. The solubility of caffeine increases with the density of supercritical carbon dioxide, thus increasing with pressure at constant temperature and decreasing with temperature increases at constant pressure. This property can be used in the separation step. Besides carbon monoxide other gases have also been proposed for decaffeination.

(d) Coffee treatments other than decaffeination: Coffees processed by methods other than decaffeination are marked in Germany. Green coffee beans are either treated for several hours with supersaturated steam or washed with dichloromethane. Roast coffee beans can be washed with liquid carbon dioxide. All of these processes are claimed to make coffee more easily digested by removing irritating substances formed at roasting or their precursors in the green bean.

3. Temperature ranges and other parameters (table)
(Ullmann's Encyclopedia of Industrial Chemistry, Vol.A7, 1994)

(a) Low-moisture processes:

Low-moisture processes, table1.jpg

(b) High-moisture processes:

High-moisture processes, table2.jpg

(c) Processes using supercritical media:

Processes using supercritical media, table3.jpg

4. Benchmark data


See information on coffee industries.

Information about chocolate, cacao & coffee production


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