Coffee Roasting

Coffee beans’ roasting is possible even in home conditions: in an oven on oiled cast-iron or iron frying pans for about an hour. Such home roasting demands big experience and attention. It is important that the internal part of coffee beans turns out fried thoroughly and the external part at the same time doesn’t burn. Coffee roasted in home conditions is of poor quality and it is difficult to compare it with professionally roasted coffee. In coffee industry coffee is roasted in four various ways: thermal (contact and convective), dielectric, radiative and by infrared rays.

The oldest is the thermal contact way of roasting when heated metal drum walls transfer warm to coffee beans creating magic taste and aroma. Such way has not found wide application, especially after appearance of convective devices in coffeeprocessing enterprises in Brazil and the USA in 1935. The current of air heated to 200 degrees in such devices paints coffee beans in chestnut colour, and different grades of coffee leads up to different degree of darkness at that. In drums fragrant beans are roasted not definitively but get only soft brown colouring allowing coffee beans to "come" at the expense of own heat. Thus uniformity of roasting is provided; beans do not contain impurity and get a brilliant surface.

At roasting by dielectric way microwave energy is used. As waves of ultrahigh frequencies are capable to get evenly deep into coffee beans irrespective of their size, balanced homogeneous taste is characteristic to the beans roasted in such a way. Such features of microwave energy allow making the roasting process continuous and faster, and coffee contains the maximum quantity of extractive substances.

The USA was the first to begin experiment application of radiating energy in coffee manufacturing. As a rule, roasting by means of such energy (in a scientifically way - energy of ionising radiation) was used for the combined ways of manufacture - at first coffee beans are examined with gamma rays, and then are roasted on standard technologies of thermal processing - but already in a shorter period of time.

As a way in manufacture infra-red rays are also applied. For each grade of coffee optimum roasting modes are figured out - temperature and time combination. And time intervals are estimated in minutes and even seconds. Sometimes superfluous seconds can become critical – beans char and lose the valuable properties.

In the course of thermal processing coffee beans increase in size but simultaneously lose flesh about 20 percent at the expense of evaporation of water, combustion of extraneous particles and decomposition of some substances. But at roasting a new element - cafeol is born – it allows us to enjoy fine aroma of roasted coffee.

There are some steps of roasting:

Not roasted:

Properties of coffee - Raw beans, 12 % humidity.Temperature, ºС - roomSigns - Green (pale-grey with a greenish shade) and smooth.

Brown:

Properties of coffee - Steam release forces a bean to extend.Loss of weight, % - 13,0Temperature, ºС - 93-135ºSigns - Light brown colour. Light taste saturation, weak aroma with a bread smell. Absence of oil on a surface.

American:

Properties of coffee - Beans continue to increase in size. The first “crack” is audible. The acid maintenance is bigger than sugar.Loss of weight, % - 14,0Temperature, ºС - 168-190ºSigns - Moderate light brown colour, with a dry surface, bit of sourness. Increase in size.

City:

Properties of coffee - Strong increase in bean. The stage of «the first crack» comes to an end.Loss of weight, % - 15,0Temperature, ºС - 198-218ºSigns - Beans crack because of the allocated gases.

Full City:

Properties of coffee - Beans strongly increase in size. Balance of acids and sugar. The stage of «the second crack» beginsLoss of weight, % - 16,5Temperature, ºС - 223-229ºSigns - Brown colour of an average saturation, basically with a dry surface, with oil traces. Balanced acidity, full saturation of taste.

Viennese:

Properties of coffee - The gas most part is lost., the stage of «the second crack» comes to the end.Loss of weight, % - 17,0Temperature, ºС - 229-235ºSigns - Bright brown colour, occurrence of drops of oil on surfaces, sweetish-bitter tones of taste. Muffled acidity, strong saturation.

Espresso:

Properties of coffee - Aroma reduction, sugar caramelization.Loss of weight, % - 18,0Temperature, ºС - 235-240ºSigns - Dark brilliant surface with oil stains. Sweetish-bitter taste dominates. Acidity is muffled.

French:

Properties of coffee - Radical reduction of acidity, sugar caramelization.Loss of weight, % - 19,0Temperature, ºС - 240-246ºSigns - Dark black colour, beans are covered by oil. A smell of burnt oil. Distinctions, characteristic for green coffee are completely muffled. Bitter - sweet-bitter taste dominates.

Italian:

Properties of coffee - The bean loses characteristic aroma of coffee.Loss of weight, % - 20,0Temperature, ºС - 246-262ºSigns - Black, dry brilliant surface. Burnt bitter taste dominates.