Our daily “Decaf” is another good example of the presence of chemistry in our day-to-day lives.
The first process for obtaining decaffeinated coffee washed the coffee beans with an organic solvent – the same solvent used in paints and varnishes – which dissolved caffeine… but also dissolved the compounds that gave coffee its aroma and flavour, leaving it… with no smell or taste! In addition, there was always the danger of the solvent residue in the grains, with the consequent adverse effects for those looking for a supposedly healthier version of coffee.
The situation changed with the discovery of supercritical fluids and their properties as solvents.
To better understand this process let’s talk about the changes of states of matter with pressure and temperature. For example, at atmospheric pressure and room temperature carbon dioxide is a gas, but with an increase in pressure it can become a liquid, and if we lower the temperature it becomes a solid. If we increase both the temperature and the pressure, it reaches a new state and becomes a supercritical fluid – presenting properties of both a liquid and a gas. That is, a gas with the density of a liquid.
Nowadays, caffeine is removed by washing the coffee with supercritical carbon dioxide under conditions in which the caffeine dissolves and the coffee aroma compounds do not. When the coffee, already decaf, returns to atmospheric pressure, the carbon dioxide evaporates leaving no trace. And even if some remains, it poses no health problems, since carbon dioxide is part of our metabolism.
So, thanks to chemistry, we can enjoy the taste and aroma of coffee without the harmful effects of caffeine.