Updated: Feb 29
Coffee Beans - the seeds of the cherries on the coffee tree.
Each cherry usually contains 2 beans whose flat side faces each other surrounded by mucilage and parchment. Green coffee beans offering very little in the way we relate to coffee taste and aroma.
Roasting green coffee creates hundreds of chemical changes within the bean and leads to the breakdown of thousands of compounds, with (the roaster hopes) the development of fantastic flavours and aromas when brewed, through processes such as caramelisation and the maillard reaction.
Among the many effects roasting has on the beans it causes them to:
Change in colour from green through to brown and eventually black (burnt)
Nearly double in size
Become half as dense
Gain, then lose sweetness
Become more acidic
Develop a huge number of aroma compounds
Pop loudly as they release gases and water vapour - known as first crack and second crack respectively
The goal of roasting is to optimise the flavours of coffee's soluble chemistry. Dissolved solids make up brewed coffee's taste, while dissolved volatile aromatic compounds and oils are responsible for aroma. Dissolved solids, oils and particles, mainly fragments of bean cellulose creates coffee's body.
*According to an old legend, coffee was discovered in 9th century Ethiopia when Kaldi - a farmer realised his goats were becoming frisky and energetic from eating natural coffee trees!