First and foremost, the amount of naturally occurring caffeine in coffee depends primarily on the botanical variety (arabica beans versus robusta beans).  Arabica beans are primarily offered by specialty coffee roasters and contain about half the caffeine of the robusta variety found in most commercial brands of coffee.  The level or degree of roast is also a factor in determining caffeine content.  Darker roasts contain lower levels of caffeine since their higher roast temperatures break down the caffeine molecules.  Contrary to what most coffee drinkers believe, it is the darker roast that has less caffeine.  Other less influential factors include the type of grind and the brewing method.  Course grinds and fast brewing methods lead to poor extraction.  While a finer grind or slower brewing method would more fully extract the coffee liquor along with its caffeine content.   So choosing an arabica bean that has been roasted to a darker level, will limit the caffeine in your brewed cup.  However, if caffeine sensitivity is an issue, you may want to buy decaffeinated coffee beans.

In order for coffee to qualify as decaffeinated coffee, it must have a minimum of 97% of its caffeine removed.  Many of us are in the dark when it comes to knowing and understanding the processes that take place in order to decaffeinate our coffee.  The following should offer some clarification.

The decaffeination processes that dominate the specialty coffee market at this time are the direct extraction and indirect extraction methods of decaffeinating beans.  Note that in all the decaffeination processes listed below, un-roasted green beans are first soaked in water and/or steamed for several hours to make the caffeine soluble and ready for extracting. 

DIRECT EXTRACTION METHODS
In the direct extraction method, the green beans come into direct contact with the decaffeinating agent (usually a solvent) after being softened by steam.  Solvent methods remove the caffeine better than water extraction methods because the solvent can target caffeine more evenly and effectively.

Methylene Chloride
This direct extraction method is sometimes called the “European Process”.  After being softened by steam, the green beans are repeatedly rinsed with methylene chloride, which removes the caffeine from the beans and forms a solvent and caffeine solution. The solution is then drained away and the beans are steamed again to evaporate any remaining solvent.  Finally, the beans are dried to ready them for the roasting process.  During the roasting process, coffee reaches internal temperatures of over 450° F (and methylene chloride volatizes at about 104° F), so any remaining solvent residues left in the green bean after decaffeination (and these are trace values) are essentially burned off during the roast.

Since the delicate and vital coffee oils and flavours are kept within the green bean during this process, it is generally considered the least destructive to coffee taste. 

Triglycerides
Direct extraction method: green beans are soaked in a hot "flavour-charged water" solution to draw the caffeine to the surface of the beans.  The beans are then removed from the resultant solution and immersed in coffee oils obtained from spent coffee grounds.  After several hours and high temperatures, the triglycerides in the oils remove the caffeine from the surface of the bean leaving the flavour elements inside the bean untouched.  Next, the beans are separated from the oils and dried to ready them for the roasting process.

Supercritical Carbon Dioxide
Direct extraction method: after being softened by steam, supercritical carbon dioxide is used as a selective solvent for caffeine.  The beans are immersed in carbon dioxide at temperatures around 70° C and at high pressure.  The carbon dioxide permeates the beans to extract the caffeine. The caffeine is then separated from the gas by rinsing or by absorption and the gas is re-circulated. In this method the waxy layer of the green coffee bean is retained and nothing but the caffeine is removed.  Any solvent residue remaining on the beans dissipates as a gas when the beans return to room temperature.

INDIRECT EXTRACTION METHODS
In the indirect extraction method, green beans are normally soaked in a water and coffee solution, known as “flavour-charged water”.  Because “flavour-charged water” is fully saturated, only the caffeine is drawn out of the bean, limiting the loss of essential coffee oils and flavour elements from inside the bean.  The beans are then removed from the solution and the solution is heated and treated with a decaffeinating agent.  In most indirect extraction methods, the decaffeinated solution is then re-introduced back into the bean.  However, some loss of other water-soluble components of coffee, such as carbohydrates and healthful chlorogenic acids, are lost with this method.

Methylene Chloride
Indirect extraction method: (sometimes called "water process") green beans are soaked in hot “flavour-charged water”.  Next, the solution is drained off and treated with methylene chloride to absorb the caffeine.  This new solution is then heated to evaporate the caffeinated solvent.  The now decaffeinated solution is re-introduced back into the bean and the beans are dried to ready them for the roasting process.  In this method, the solvent never comes into direct contact with the beans.

Ethyl Acetate
Decaffeinating coffee using this process is often referred to as a "natural" process because ethyl acetate is a compound found in fruits, such as apples, peaches, and pears.  The process is the same as the indirect extraction method using methylene chloride described above, although ethyl acetate requires more time to absorb the caffeine. In this method, the solvent never comes into direct contact with the beans.

Swiss Water Process
Indirect extraction method: green beans are soaked in hot "flavour-charged water."  The solution is then drained off and treated with activated charcoal filters which remove the caffeine from the solution.  Some of the "flavour-charged water" is kept and recycled to start off the process for the next batch of beans.  The caffeine-free solution is then added back to the partially dried coffee beans before they are fully dried and roasted.  This method is known as the “Swiss Water Process” because a Swiss company originally developed and patented the procedure.

Note that in both the direct extraction method and in the indirect extraction method, the decaffeinating agent is removed from the final product. 

 Some decaffeinated coffee is sometimes described as "naturally decaffeinated". This phrase suggests that the coffee has been decaffeinated by some natural process, however, no specific "natural process" currently exists.

All the methods of decaffeinating coffee beans experience some loss of flavour and aroma during the process.  It is not the loss of caffeine, which is virtually tasteless, that diminishes the taste, but rather the method used to decaffeinate, and the darkness of the final roast that ultimately determine the final cup quality. 

It is important to avoid a highly roasted decaffeinated coffee as it will have lost its top and bottom notes and a noticeable amount of its acidity.