General
When asked “what does caffeine look like?” most people tend to answer that they have not actually seen caffeine, but that it is probably a brown substance. This is understandable but this wrong assumption shows the association be- tween caffeine and coffee.
A handful of people may answer that they remember something in chemistry laboratory class in high school. That there was something about the term sublimation. Besides these aspects just about everybody knows that caffeine has a stimulating and awakening effect when consumed, well known not only from coffee and different teas but also from caffeinated soft drinks.
Summarizing, caffeine is a well-researched chemical substance with interesting properties and at least its name is widely known.
Caffeine was first isolated from coffee beans in 1820 by the chemist F. Runge at the request of the German author Johann Wolfgang von Goethe. At room conditions, pure caffeine is a white, odorless crystalline powder bitter in taste. It exhibits two different crystal forms in pure state and when crystallized in presence of water very typical whiskers are formed.
shows caffeine crystals extracted from coffee. Caffeine crystals can also be found frequently as sediments in coffee pro- pressing factories especially around roasting machines.
This is due to the previously mentioned effect of sublimation: at elevated temperatures caffeine can change from the solid to the vapor state directly without liquefaction as intermediate step. The name caffeine does not give any information about the chemical nature of the substance. It belongs to the group of methyl xanthine’s and carries the name 1,3,7-trimethylpurine-2,6-dione. The chemical structure
shows the high content of nitrogen in the caffeine molecule. The physiological effects of caffeine have been investigated for a long time and research is ongoing. Simplifying matters, positive and negative health effects have been declared, obviously depending on individual condition and consumed quantities. Important is, that the US Department of Health and Human Services classifies caffeine as a GRAS substance (generally recognized as safe).
Recently, the European Food Safety Authority stated, that “habitual caffeine consumption of 400 mg/day does not give rise to safety concerns for non-pregnant adults” . This amount corresponds roughly to five cups of regular drip coffee. Nevertheless, consumed quantities must be observed as the lethal amount in man is estimated as 10 g. Further information on the effects of caffeine on health refer to Chapter 20 in this book.
Caffeine content in green and roasted beans is roughly the same: mean values are 1.1 wt% for Arabica and 2.2 wt% for Robusta beans. It is often believed that caffeine content is reduced in roasted coffee due to sublimation. However, as weight of the bean decreases the total concentration in the bean remains roughly unchanged. Caffeine content in coffee beverages is dependent on the blend composition (% Robusta), the water to coffee ratio and extraction yields. Typical values (Arabica) are 80 , 120 mg per cup of drip coffee (150 mL) and 50,100 mg for espressos.
