Decaffeination

The decaffeinating methods

What really distinguishes one coffee type from another is the choice of solvent used during the second stage of processing:

Water Ethyl acetate Carbon dioxide Methylene chloride

Here is a brief outline of the above mentioned methods:

1. Water undoubtedly has a very good reputation on the market, however the quality of the final product is less than excellent both in terms of its physical appearance (rather dark coffee not suited for marketing before roasting) and in terms of flavour when consumed. This method that dates back to early this century has only recently been fully applied.
Over the last few years it has become economically and qualitatively viable but it still leaves a margin for improvement. If green coffee is immersed in water the caffeine contained within is removed, but along with it goes most of the coffee's aromatic character. To overcome this problem, the liquid is saturated with the water soluble components of the coffee. The result is good but bears no comparison with that of a specific solvent. Caffeine is subsequently extracted from the solution using activated carbon or solvents (i.e. water or methylene chloride) which retain the caffeine and which can then be re-used. This process should be carried out using state-of-the-art equipment on great quantities of coffee if it is to be economically viable and capable of using a large-scale economy to its full advantage. Another inevitable result is a minimal exchange of coffee components in coffees decaffeinated using the same saturated water. This causes a slight alteration in the organoleptic characteristics of the product.
An important step of the process is the regeneration of activated carbons by means of a solvent or at a determined temperature and pressure.

2. Ethyl acetate is a specific chemical solvent used in the decaffeinating process, wich can also be found in nature. It is a substance often found in fruit and therefore well-regarded.
Unfortunately it has two considerable drawbacks: it is highly explosive and has a fruity odour. Consequently production costs are quite high.
In addition, coffee decaffeinated using ethyl acetate might retain the odour of this solvent which a slight change in flavour.

3. A study of the method using Carbon dioxide in its supercritical state (i.e. between its liquid and gaseous states) or liquid state highlights the need to work at an extremely high pressure (approximately 250 atmospheres for supercritical, 70 for liquid), which therefore involves extremely high running costs. The main difference between the supercritical and liquid states lies in the extraction times, that are very long in the second case. Results are proving worthwhile, however comparatively not more favourable than those obtained using a specific solvent such as methilene chloride. The carbon dioxide method also requires large-scale production to take advantage of large-scale economies. For this reason it remains unsuitable for a market sector consisting of coffee roasters and green coffee dealers who prefer decaffeinating a limited amount of their own coffee rather than being forced to buy the fully processed product, a constraint which would prevent them from choosing single coffee types..

4. Methylene chloride is the most widely used solvent, also because it was the first to be applied to the industrial field; the process is therefore extremely perfected, even though it can be constantly improved.
It is a substance which acts selectively on caffeine and is highly volatile (evaporating at less than 40°C = 104°F), making it relatively easy to eliminate from the coffee using steam without leaving any detectable traces on the roasted product. In the opinion of many, the quality obtained using this solvent is the best of the various methods, especially for the flavour of the final product. Indeed nearly all the characteristics of normal coffee are retained except for its waxes, which are mostly eliminated, making the coffee lighter and easier to digest.
Undoubtedly this method can be considered the best both qualitatively and economically; in the past, it has aroused antagonism in those who claim that the type of solvent used poses a health risk. Dichloromethane was fully tested in the United States and in the EU, both of which agreed in sanctioning its non-harmful nature for decaffeinating purposes at the maximum levels permitted by law. It must also be considered that:

the actual maximum residue levels in the coffee are always well below those permitted in order to maintain a margin of safety. And also because it is in the interest of each producer to salvage the solvent since it is very expensive;
coffee is roasted at very high temperatures which wouldmake any residual solvent volatilize, given that it evaporates at 40°C = 104°F;
supposing something remained in the coffee after roasting, only a minute amount would reach the cup since not all substances present in ground coffee powder can be found in the drink made from it.

Hopefully debates regarding this issue will cease now that the United States Food and Drug Administration and the EU have both sanctioned the use of this solvent in coffee decaffeinating procedures.