ART OF ROASTING
Roasting is an extremely important element in the quality of a coffee.
In order to ensure the blends are ever-lasting, a coffee roaster must import large stocks of green coffee beans.
Most coffee travels by sea via the port of Antwerp. It is generally packed in 60 kg jute bags.
If the green coffee beans are “organically grown” they must be stored separately from other coffees.
EXAMINING GREEN COFFEE BEANS
Green coffee beans are gauged first of all by appearance, especially with regard to the number of defective grains per 300 grams.
But this is not enough: only tasting reveals all the qualities and weaknesses of a sample. This is done in a laboratory.
CHANGES THAT TAKE PLACE DURING ROASTING
When exposed to heat, sugar and water combine to make toffee.
By the tenth minute, when there is no more water, the sugar and acid begin to release their aromas… just three to begin with, then developing up to a thousand.
These are known as the Maillard reactions, named after the chemist who studied this complex phenomenon.
Traditional roasting is done using gas burners, which heat the oven to a temperature of 220°C. The green coffee beans are fed into the oven through a funnel. The arrival of this cold mass causes the temperature to drop to 120°C. It climbs back up to 220°C in the space of 20 minutes.
Roasting is controlled automatically for the first 17 minutes, then an operator takes over and relies on the appearance, smell and sound of the coffee. To do this, he uses a probe to withdraw a few grains. When the coffee is ready, it is dropped into a cooling tray. The blue smoke is due to the presence of anhydrous carbon, an aroma-carrying gas.
Once roasted, the weight of the coffee has decreased by 20 % but its volume has increased by 60 % There is another method for cooling the coffee, using water.
This is not fraudulent in any way because by law, roast coffee beans may contain up to 5% water but there is a disadvantage: the water oxidises the coffee, blocks the aroma and adds to the weight of the packet of coffee sold.
10 MINUTE QUICK-ROAST
The coffee is placed in «towers» through which very hot air (360 °) is blasted by 60 hp turbines. The roasting is completed in 10 minutes, which means it is stopped exactly when the Maillard reactions begin to take place.
This method produces coffee whose pigmentation has changed, but it has lost its acidity, gained in bitterness and barely 30 % of the aroma has been released. Moreover, the coffee beans are so hot that the only way to cool them is using water.
90 SECOND FLASH-ROAST
The coffee is roasted at a very high temperature when it is bombarded by waves. At this speed and this temperature, the Maillard reactions cannot take place. The coffee beans are quite simply burned on the outside and raw inside. They are also cooled in water. This is by far the most economic method – the biggest coffee-roasters of the world use it – but it is also the worst.
THE DIFFERENT TYPES OF COFFEE-ROASTING
“Blonde” roasting is commonly used in Finland and northern countries. It produces a light coffee which is acidic but not bitter.
“Monk’s pants” roasting is used in Germany and in the United States. This method produces a light coffee which is slightly less acidic and only very slightly more bitter.
Continental torrefaction, which is the method used in France and northern Italy, is halfway between acidity and bitterness.
Finally, Neapolitan or Spanish roasting produces a coffee which is not at all acidic but very bitter.
Further down the line, the laboratory supervises the quality of the roasted coffee beans.
To analyse the final aroma, it carries out chromatographic analyses which permit the presence of different aromatic components to be detected.
It is also in the laboratory that the humidity, grain size and colour are inspected.
Once roasted, the coffee continues to live.
First of all, the aromas freed by the roasting continue to develop… hence the wonderful smell that prevails in the coffee-roaster’s shop.
It then ages but unlike wine, this does not improve it: coffee beans start to oxidise after three weeks; ground coffee oxidises within five days. To protect it from this process, coffee is vacuum-wrapped as soon as it has been roasted, which means it can then be stored for a long time.
Finally, the seal of tins is often raised – this is in fact a sign of quality.