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Coffee processing consists of removing the skin, pulp, parchment and silver screen. The quality of the final product depends upon the method of processing.
Two methods are employed for processing
- Dry method
In the dry method, the beans are sun dried.
- Wet method
In the wet method, known as the washed coffee process, pectin enzymes are used on selectively picked cherries to replace spontaneous fermentation.
Figure: Coffee curing process
The manufacture of coffee powder involves roasting, grinding, blending and packing.
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Roasting:The degree of roasting is one of the important factors influencing the quality of coffee. The typical coffee aroma is developed during roasting.
The flavour and aroma of coffee are best when it is freshly roasted and deteriorate on standing. The flavour is largely due to 2-thiofuran and its methyl and ethyl esters, together with some other sulphur compounds. The aroma of coffee is partly attributable to mercaptans present in the roasted beans.
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Grinding: The bulk of roasted beans is ground to powder and sold as ground coffee. Roasted beans are ground to three sizes, namely, fine, medium and coarse. Coarse ground powder retains aroma and flavour better and longer than fine ground powder.
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Blending: Blending of Arabica and robusta in the ratio of 2:1 and addition of roasted chicory root powder at 10 % level to the blend gives a strong decoction with good aroma.
Strength, flavour, aroma and acidity are the chief criteria in judging the quality of coffee and judicious blending of different grades brings out these qualities to the best advantage.
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Packaging: For larger packs of roasted and ground coffee, gas packing under carbon dioxide or vacuum is effective. For unit packs, various flexible films like polyethylene, cellulose films, high density polyethylene and for short duration storage, the high density polyethylene is effective.
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Instant coffee: Instant coffee is made by dehydrating coffee brew. The steps involved in the manufacture are
- Extraction of coffee powder
- Dehydration of extract and
- Recovery of volatile flavouring compounds and their addition to instant coffee.
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Chicory: Chicory root is chopped, roasted and ground and is used as a substitute for coffee often blended at 50 percent level. It gives bitterness and body to the beverage which some people find refreshing. It is not harmful to the body. It produces a dark infusion with laxative properties and does not have caffeine.
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Adulterants of coffee:
- If chicory is added and not mentioned on the label, it is considered as adulterant.
- Cherry husk is sometimes used as an adulterant.
- Burnt sugar, tamarind seed, used coffee powder and saw dust are also used as adulterants.
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Coffee beverage: Coffee is used mainly as a beverage in the form of aqueous extract prepared from roasted and powdered beans. Coffee has no food value. The constituents that are of chief significance in the making of the beverage are caffeine, flavour substances and bitter substances.
- Caffeine : It is an alkaloid substance producing the stimulating property. Caffeine stimulates the central nervous system. It is also a cardiac stimulant. It is a diuretic. It increases gastric and pepsin secretion. Excessive intake can cause insomnia.
- Flavour substances: It is the sulphur compounds that are the main contributors to the flavour. Too long heating and too high a temperature may destroy all characteristic flavour and aroma.
- Bitter substances: Polyphenol substances or tannins are hot water soluble. Hence longer the coffee is brewed, the greater will be the tannin content and the bitterness becomes pronounced.
Table: Summary of different methods of making coffee.
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Method
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Flavour
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Tannins
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Limitations
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Filtration
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Retains well
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Extracts less
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Decoction may not be hot
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Vacuum coffee maker
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Retains well
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Extraction is more due to the contact with the grounds at a high temperature for few minutes.
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More bitter
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Percolator
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Loss of flavour due to constant aeration of the brew as the liquid is forced up and sprayed the grounds.
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Extraction is more due to recirculation of hot water through the coffee grounds.
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More bitter
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Steeping
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Retains best
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Extracts less
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Extraction of flavour may not be complete
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