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Caffeine is only one of several hundred chemicals found in coffee. However it is the most notorious because of the many physiological affects it has on the human body. Caffeine naturally occurs in many other plants apart from the coffee bush, such as tea and cocoa plants.

There is a long established link between coffee and mental stimulation, which gives a cup of coffee a certain appeal. In fact it could be argued that coffee drinking has helped change the course of history. In 1773, it was in a Boston coffee house where citizens planned the Boston Tea Party; and in 1789, it was from Caf' Foy that Camille Desmoulins led the angry mob that later brought down the Bastille.

Whether caffeine is actually good for us is a long and much argued debate. Caffeine is commonly used by endurance athletes to permit them to train for longer and aid their recovery afterwards. Scientific studies have also linked it to the prevention of Parkinson's and Alzheimer's disease. However, too much caffeine can lead to insomnia, diuresis, gastro-intestinal disturbance, arrhythmia, psychomotor agitation and osteoporosis.

The amount of caffeine in an average cup of coffee (8oz/230ml) varies from between 80 to 150 milligrams. This variation is due to a number of factors. The main difference is caused by from where, and from which variety of plant, the coffee beans are harvested. As caffeine has natural anti-fungal properties, coffee plants grown in environments less favourable to the growth of fungal spores contain less caffeine. At high altitudes, the temperature and humidity is such that spores germinate too slowly to have too much of an effect on a coffee plant. So, generally speaking, the higher the altitude at which a bean is grown, the lower its caffeine content. Also Arabica beans typically have half the amount of caffeine when compared to Robusta beans.

The roasting process alters the amount of caffeine in a coffee bean. A common misconception is that, the darker the roast level, the lower the caffeine content. However, this is not really the case as caffeine changes very little during the roasting process. Caffeine has a very stable structure with a boiling point above 315'C, well above roasting temperatures, which rarely exceed 245'C. Nevertheless a small amount of caffeine is lost due to sublimation, where a substance changes directly from a solid state to a gaseous one. This occurs in caffeine at approximately 175'C.

The roasting process dramatically alters a coffee bean. A bean loses weight, mostly due to water evaporation, causing the level of caffeine by weight to increase. However, as beans nearly double in size when roasting, the level of caffeine by volume decreases.

The final factor affecting the caffeine content of your cup of coffee is the brewing method. Different brewing methods require different amounts of coffee, ground to different sizes. Many people believe that an espresso contains less caffeine then a regular cup of coffee. But as you require more coffee to make an espresso then a regular cup, and the coffee is ground finer, increasing the surface area, this means that the caffeine content is roughly the same. However the effects will be felt more quickly with an espresso, and wear off faster, as caffeine is absorbed more rapidly when taken in concentrated doses.