The treatment of decaffeination can be carried out in different ways, that are different one from the other only for the kind of solvent used during the phase of caffeine extraction. All these methods have in common the main steps of the process, that are the following ones:
1. VAPORIZATION: The raw coffee is treated with steam to swell the beans that, spacing their molecules, allow an easier caffeine extraction;
2. EXTRACTION: Coffee is submitted to the action of a special solvent authorized by the law (water, carbon dioxide, ethyl acetate, dichloromethane);
3. SOLVENT RECOVERY: The solvent residues are recovered and later re-used for other treatments of decaffeination: this step is carried out with particular care both for economic reasons (all these products have a very expensive cost and therefore the wastes must be reduced) and for legal reasons (the law regulates the maximum residues limits);
4. DRYING: Most of the present humidity is eliminated from coffee;
5. PACKAGE: Coffee is then packed inside its bags;
6. ANALYSIS: The residues of caffeine, solvent and humidity are then analyzed. The decaffeination is carried out with the use of the following solvents, that are substances able to dissolve an alimentary product or components of an alimentary product and that are classified as technologic co adjuvant, having the chemical-physical and purity characteristics indicated in the attachment of the M.D. 20.5.1976;
a. WATER: It gives not excellent results, both for the coffee appearance, that looks very dark and unsuitable to the sale before being roasted, and for the coffee taste in the cup. It is an old technology (dating back to the first half of the century) applied recently and that only during the last years became economically and qualitatively possible.
By dipping the green coffee in the water caffeine is removed, but together with caffeine also most part of the aromas are removed. In order to avoid this inconvenience the liquid was saturated with the components of coffee that are soluble in water. The obtained result was good, but not comparable to the one obtained with a specific solvent that only acted to caffeine. Caffeine is then extracted from this liquid passing through some active carbon that recovers it to be re-used. All this must be carried out in a sophisticate way and for a big quantity in order to obtain a process that is economically possible exploiting scale economies. Moreover, during this process there is a little interchange of components between the decaffeinated coffees and the saturated water that is impossible to avoid and that lightly modifies the organoleptic characteristics of the product.
b. ETHYL ACETATE: This is a chemical non-toxic solvent specific for decaffeination that is naturally in coffee and fruit. It has two disadvantages: it is highly explosive and it has a strong fruit odour. This involves a production cost that, even if it is cheaper than water and carbon dioxide, it is quite expensive. Moreover, coffee decaffeinated with this method acquires the odour of the used solvent, lightly altering the taste.
c. CARBON DIOXIDE: The process using carbon dioxide at the supercritical state (i.e. a state that is the limit between the liquid and the gas state) forces to work at very high pressures (more than 200 bars) and for this reason it is extremely expensive. The method is rather new, and the quantity to be processed must exploit the scale economy.
d. DICHLOROMETHANE: It is the most used and diffused solvent, also because it was the first to be used at industrial level. It is a substance that exclusively acts on caffeine, it is highly volatile (it evaporates at 40°C) and therefore easily eliminated from coffee by the steam, leaving only unperceivable traces. According to the experts, the quality obtained with this solvent is the best both as appearance of the green decaffeinated coffee and as taste in the cup (most of the characteristics of coffee are in fact preserved, with the exception of the greases that, being partially eliminated, make the coffee lighter and more digestible).