Instant coffee
In commercial processes the decaffeination of instant coffee almost always happens before the critical roasting process which will determine the coffee's flavour and aroma characteristics.
Modern processes use one of two common decaffeination methods, solvent extraction or water extraction.
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Solvent Decaffeination
The most commonly used solvents are trichloroethylene, methylene chloride or a similar chlorinated hydrocarbon. More recently, supercritical carbon dioxide has been used as an alternative solvent to the more hazardous chlorinated hydrocarbons.
In order for solvent decaffeination to function additional moisture is required in the coffee bean. The method for introducing this moisture does not matter -- the importance is the water content of the bean, and typically anything between 18% and 55% is sufficient. The moisture is required to soften the cellular structure of the bean.
- Basic steps of solvent decaffeination
- Steaming of coffee beans for 30 minutes at 230 °F (110 °C).
- Increase of coffee bean moisture content to above 40%.
- Beans flow through extractor columns with solvent at temperatures between 120 °F and 250 °F (50 °C to 120 °C). Caffeine is removed from beans.
- Decaffeinated beans are "steam stripped" of solvent for 90 minutes.
- Decaffeinated beans are removed from extractors and dried.
- Caffeine rich solvent is recycled to be used in step 2.
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Water decaffeination
Water extraction of caffeine was first patented in 1941 by General Foods. Its claimed advantages are:
- Higher extraction rates
- Caffeine recovery by this method produces a purer product
- Less heat treatment of the coffee bean
- No direct solvent contact with the bean
This method takes about 8 hours, considerably longer than solvent decaffeination; however it does seem to produce a better quality end product.
The basic method involves the use of a water extract of green coffee beans in a battery of columns in contact, countercurrently, with green beans. As contact is made the green beans preferentially absorb water. The solid content of the water extract of green beans doubles (from 15% to 30%) as caffeine is taken up. During the 8 hour process about 98% of the caffeine is removed, which is comparable with the solvent extraction method. The decaffeinated beans, now 58% moisture by weight, are washed and dried.
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Regulatory context
In the EU, regulations include the following details:
- Species of coffee bean
- Geographical origin
- Processing detail
- Year of crop
- Solvents used in decaffeination
- Caffeine level
Various institutions govern the coffee industry and help to achieve standardisation and also release information to the public.
- International Coffee Organisation (London)
- Codex Alimentarius Commission of the UN (Rome)
- National Coffee Association (New York)
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Bibliography
- (1993) in Romualdo Verzosa Jr.: Encyclopedia of Chemical Technology, volume 6, 4th Edition, John Wiley & Sons. ISBN 0-471-52674-6.
- Masters, K (1991). Spray Drying Handbook, 5th Edition, Longman Scientific & Technical. ISBN 0-582-06266-7.
- (1995) in John J. McKetta: Encyclopedia of Chemical Processing and Design. ISBN 0-8247-2604-9.
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External links
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