MAIN PROCESSING STAGES
Green coffee can be decaffeinated using various extraction processes, which can mostly be differentiated based on the solvent used for the extraction. The processing stages apply to all the various methods, and include:
Steaming: The coffee is treated with water and steam, which starts the extraction process and makes the beans expand. This stretches the cellular structure within each bean, and therefore facilitates the extraction of the caffeine.
Extraction: The coffee is then rinsed with a specific solvent, which 'captures' the caffeine and removes it from the bean.
Recovery of the solvent: Almost all of the solvent can be recovered from the coffee, and can then be re-used. This stage is carried out with great care both for financial reasons (all the products used are very expensive and so waste must be kept to a minimum) and for legal reasons, since there are legal limits concerning the maximum quantity of residue.
Moisture removal: Almost all of the moisture in the coffee is removed.
Packing: The coffee is packed into its original bags or into new bags provided by the client.
Testing: The coffee's residual caffeine content (not in excess of 0.1% allowed by law in Italy and most of Europe), residual solvent content (not in excess of 2 p.p.m. of dichloromethane for roasted coffee) and moisture content (no higher than of 11% allowed by Italian law) are tested.
EXTRACTION SOLVENTS
1. WATER: Using water as a solvent has excellent commercial appeal, and in fact it was one of the first solvents to be used for decaffeination. It is rather complicated to use because it is not particularly selective, so it extracts some of the water soluble flavour components from the product, along with the caffeine. Various methods are used to get around these drawbacks. The water can be saturated in advance with the flavours that the coffee normally contains, thus reducing the extent to which they are extracted from the processed coffee. However, this leads to a certain degree of molecule exchange between the solution and the coffee, which alters the product's characteristics. An alternative is to extract the caffeine and the water soluble flavours, remove the caffeine from the solution using a solvent or activated carbon, and then allow the coffee to reabsorb the molecules it lost during the extraction process. Recent developments in the processing method have made this extraction system viable, both financially and in quality terms. The raw product obtained is relatively dark, but this ceases to be an issue after roasting. This method is rather complicated, and needs to be carried out following parameters and roasting curves defined specifically for each product.
2. ETHYL ACETATE: Ethyl acetate is a selective solvent for caffeine and a natural component of many fruits, and it is therefore well thought of amongst consumers (actually extraction processes use mainly a synthetic version). It has two considerable drawbacks: it is highly flammable and has a fruity aroma. It must therefore be handled carefully, increasing production costs, and it tends to pass on its characteristic aroma to the coffee, slightly altering the flavour.
3. SUPERCRITICAL CARBON DIOXIDE: This process is conducted at extremely high pressure and high temperatures, which cause the carbon dioxide to pass into its supercritical state, with properties midway between a liquid and a gas. In these conditions the carbon dioxide becomes a selective and quick solvent, making it suitable for removing caffeine from coffee. The equipment needed for this type of processing is very expensive, as it has to function at exceptionally high pressure (250-300 bar) and implies high running costs. In addition, the process requires a significant amount of energy, and so it can only feasibly be used on sizeable quantities of the product. This makes it unviable for people who want to decaffeinate smaller quantities of coffee.
4. LIQUID CARBON DIOXIDE: To avoid the extremely high pressure required for supercritical extraction, sub-critical conditions (liquid carbon dioxide) have been tested. This allows the decaffeination to take place at lower temperatures (20-25°C) and reduced, though by no means low, pressures (65-70 bar). This slows down the caffeine extraction process considerably, increasing processing time.
5. DICHLOROMETHANE: Dichloromethane is the most widely used solvent for decaffeinating green coffee, and it was one of the first to be used at an industrial level. This technique is therefore already highly honed, although it is still constantly being improved. Dichloromethane is a very volatile substance (it evaporates at 40°C) which acts selectively on caffeine and is relatively easy to remove from coffee through steam. It results in a very high quality product, as the highly selective nature of the solvent leaves the organoleptic properties of the original coffee intact. Demus' dichloromethane decaffeination process also removes the waxes present in the beans (C-5-HT), making the coffee lighter and easier to digest.
