Coffee roasting, is a highly important phase of the coffee production process: the Italian term “torrefazione” used for this process derives from the Latin torrefacere and means “to dry”.
It is based on a procedure that may seem banal, since it consists of simply cooking the raw beans.
Actually, the ideal roasting point of every variety of coffee needs to be known, in order to ensure that the aromatic profile remains intact.
Coffee roasting began long ago and has evolved over the centuries: today we will be finding out more about its origins, how it has developed and how the machines for roasting the beans, “bean roasters” have developed over time.
When did coffee roasting first begin?
It is impossible to establish exactly when roasting first began: indeed there are many legends and stories told about this, but it would appear, as in the case of so many other discoveries, that pure coincidence played a fundamental role.
According to some, the origins of this method date back to the time after the siege of Vienna (1529) by the Turks, led by Soliman the Magnificent.
The soldiers used sacks full of coffee beans for shelter and, when the invaders set the city on fire, the coffee was toasted.
An even older Arab legend claims, on the other hand, that some coffee beans ended up by mistake on the embers of a camp fire and drew the attention of all those present with their enveloping fragrance.
The first roasting methods
Coffee roasting was first carried out using utensils in metal or porcelain: in the Ottoman Empire, round, thin pans, often with holes in, were used, and had a long handle which was used to place them over a brazier.
A spoon was used to mix the small quantity of beans cooked.
In Egypt, more specifically in Cairo, in 1650 the Coffee roaster made its first appearance : it consisted of a metal cylinder with an external crank connected to a type of internal blade which allowed the beans to be stirred.
This rudimentary roasting machine was made of cast iron or copper and placed on top of a brazier.
It gradually became common throughout the rest of the world, undergoing modifications in the various countries and becoming increasingly modern.
Anyway, these machines for roasting coffee beans remained common throughout the 20th century: in Italy for example, the “tostino” or roasting pan consisted of a pan with a lid, a crank and a door for placing the coffee beans inside and was also used after the second world war.
But the roasting process was soon transferred to factories: the roasting machines disappeared from the bars and the same happened with the household models.
Coffee Roasting: how does the coffee roasting machine work?
Before dealing with this aspect, it might be useful to remember that the perfect coffee roasting is influenced above all by:
- the heat administration;
- the suitability of the type of roasting for the type of coffee used;
- an appropriate and fast cooling method.
A good roasting machine, manages to achieve a harmonious balance between these factors and regulate them in the best way.
Almost all the machines consist of a metal cylinder with an internal blade system which guarantees the right level of mixing and even exposure of all the beans to the heat.
The heat needed for the roasting is normally produced in a combustion chamber heated by a gas combustion burner.
Starting from the early 20th century, this type of fuel replaced wood and coal, while some small machines, in the range of 1-2 kg, are heated electrically.
There are two main roasting systems, conduction and convection, plus a third method which consists of a cross between the first two. Let’s take a look at the characteristics of each one.
Conduction roasting system
With this roasting system, the heat energy is transferred to the coffee through direct contact, from the metal walls of the cylinder which are heated by a heat source positioned below.
Although very common in the past, this method does not allow perfect control of the roasting process: it is easily liable to lead to scorching, ie. burning or scraping, which is an unpleasant inconvenience.
The roasting effect obtained can also be very uneven, and this can also have negative effects on the flavor of the drink served.
In fact coffee has a low level of thermal conductivity which impedes the transfer of heat within the bean: so with this method there is a strong probability of obtaining beans cooked only on the surface and raw inside.
The scorching also causes another phenomenon: the coffee in contact with the metal walls of the cylinder, actually causes small flakes, called Tips, to come off the beans, and in the extraction process these can give the coffee a very sour taste.
This conduction system is now almost completely obsolete.
Hybrid roasting system
The adoption of gas as a fuel to heat the combustion chamber made it easier to control the heat.
In fact, with the appropriate modifications made to the cylinders, no longer closed, but perforated at the back to allow ventilation, the roasting process has changed to become partially dependent on a flow of hot air, rather than totally dependent on the heat transmitted by the walls of the cylinder.
This type of hybrid roasting still exists, and has its combustion chamber connected below the cylinder, but separated by a layer of insulating refractory material.
In this way, there is less direct conduction of heat directly onto the metal walls of the cylinder, while the hot air pumped into the rotating cylinder acts directly on the coffee beans.
The hybrid model contributed to improving the final result on the coffee beans compared to the conduction method.
This is the reason why the most qualified manufacturing companies continued their technical development in this direction until they obtained a roasting method which uses mostly hot air, or rather, convection.
Convection Roasting system
This is the method used by the most modern roasting machines: the beans are cooked by convection, via the use of hot air which flows in and is pumped forcibly into the cooking drum of the machine.
The air is pre-heated in a separate combustion chamber thanks to a modular burner.
The coffee is roasted using the air, and the direct contact with the hot metal of the cylinder is almost non-existent.
Convection roasting guarantees an even result, both on the outside and the inside of the coffee bean, and ensures the necessary chemical-physical transformations needed to obtain a roasted coffee from which it is possible to make the perfect espresso.
Convection roasting machines allow for optimization of the variables of volume and temperature of the air pumped in, as well as the modulation and power of the burner and the rotation speed of the cooking drum.
In this way, it is possible to obtain different roasting profiles, which range from 374 °F to 428 °F, while the time may vary from 8 to 20 minutes.
The roasting process is a highly delicate step: it requires experience, passion and continuous research.
It is an operation which needs to be adapted to the type of coffee used, the areas it is going to be sent to, and the taste of the consumers.
Did you know about its history and evolution?