Coffee knowledge

The coffee plant

Coffee is a cherry. It is the seed of a tropical plant of the Rubiaceae family. It grows at an altitude between 400 and 2000 metres and at a temperature between 20° and 25° C. About 60 species of coffee are grown but the most commonly used all over the world are Arabica and Robusta. Once mature, a coffee plant produces an average of 1 kilo of raw “green” coffee beans per year. These coffees are the subjects of a lot of misinformation, often perpetuated by coffee companies. Arabica is the most valued for its aroma whereas Robusta gives body to the coffee. The Arabica beans are flat and elongated while Robusta’s are small and rounder. A coffee plant can grow up to eight metres high. It produces a cherry-like fruit, which turns bright red when it is ripe. It contains two seeds covered with a thin silvery membrane; which are the coffee beans. The arabica beans are usually regarded as the premium variety. Many roasters will make much of the “100% arabica” content of their roasts. These beans tend to be grown in more mountainous regions, over 800 meters above sea level, where disease is less prevalent. As such, harvesting is more labour-intensive. For this reason arabica beans command a higher value on the market. The robusta beans, as their name suggest, are less susceptible to disease and can be grown at lower altitude, from sea level upwards. They tend to cost less as they can often be harvested by machine. That arabica is always superior to robusta is complete nonsense. There are some downright lousy arabicas on the market, as well as some truly exceptional robustas. Lots of the top espresso blends contain a small amount of the best robustas. The berries are harvested either by hand or mechanically. The beans are harvested by machine (in flatter areas, for lower quality beans) or by band (in sloping areas, for higher quality beans) and are usually exported to coffee roasters in their green state. Harvesting by hand will gather only the ripe berries, while mechanical picking will gather all berries thus producing unevenly mixed batches. The berries are treated with two different processes: dry and wet, in both cases the beans are separated from the pulp and impurities. The coffee beans are the packed in 60-kilo bags and sold all over the world.

Roasting

Roasting differs from country to country. In European countries the beans are usually roasted to a «monk’s cowl» brown. Each roaster uses it’s own blend, usually made up of three to eight types of green coffee. The beans are roasted at a temperature of 200°-220 °C, the process taking from ten to fifteen minutes. During this phase internal gasses swell the beans, and cause an increase of volume of about 60% with a weight loss of 20%. There are about 800 volatile aromas in one coffee bean.

The chemical composition of unroasted coffee is as follows:

• Water 12%
• Nitrogenous substance 12%
• Sugar and dextrin 10%
• Cellulose24%
• Non-nitrogenous extractive substances 18%
• Ash 4%
• Caffettannin acid 6.7%
• Caffeine 1.2%
• Essentialoils 0.1%

After roasting there is a substantial decrease in the water percentage, which is the principle cause of weight loss. The roasted coffee must not be exposed to air for too long because the fatty substances turn rancid resulting in an «off-taste» in the cup. Volatile substances trapped inside the bean, so the methods of grinding and preserving the coffee are fundamental in obtaining a good cup of espresso coffee create coffee’s aroma.