Caffeine and Decaf

Coffee contains all sorts of exotic compounds which give it its flavour and aroma. However, its main biologically active compound is caffeine (1,3,7-trimethylxanthine or 3,7-dihydro-1,3,7-trimethyl-1H-purine) C8H10N4O2.

Caffeine is an adenosine antagonist. It acts at adenosine receptors and blocks them, causing adenosine to circulate longer in the body, increasing its stimulatory effects. (Caffeine inhibits cAMP phosphodiesterase). It increases the output of epinephrinecaff-graph and norepinephrine from the adrenal glands. It is a GABA antagonist.

Caffeine takes effect about five minutes after ingestion, with serum levels peaking after about 30 minutes. The body takes three to six hours to metabolise and fully excrete the caffeine.


Decaffeinated Coffee

There are about five techniques in commercial use for decaffeinating coffee. Some utilize chemicals with nasty sounding names, one uses pressurized carbon dioxide and another just uses really hot water. It may not be a popular sentiment, but the best tasting decaffeinated coffees are in fact chemically processed.

Caffeine has an unbelievably high solubility in dichloromethane (DCM) and this is used to advantage in the decaffeination process. This process involves making up a stock batch of coffee in a large tank within a large semi-permeable membrane. DCM is then passed through this tank, carrying away the caffeine, which is usually recovered for use in cola drinks or medication. The coffee to be decaffeinated is put into the tank on the other side of the semi-permeable membrane and DCM is continually passed through the stock batch. As soon as the caffeine in the new batch is drawn across the membrane into the stock batch, it is extracted by the DCM, causing more caffeine to flow across -- ie, perturbing the equilibrium to one side (Le Chatelier's principle) until all caffeine is removed from the new batch. Once all caffeine has been removed, the new batch is removed and replaced with another.

Other methods involve pressurized carbon dioxide or very hot water.  Often the coffee flavor is extracted from the beans along with the caffeine, which must then be reintroduced to the rather bland beans to restore flavor in the last step.

What were you expecting when you let a medical physicist roast your coffee!