The flavor potential of coffee beans is revealed by good roasting, which is not possible without good equipment. In this article, we tell interesting things about the development history of roasters and also explain the basic concepts of coffee roasting.
Legend or historical fact, but the first coffee roaster was a certain Omar of Arabia who lived in the 13th century. Omar roasted coffee cherries to soften the bitter taste of the beans. This is approximately how the Arabs obtained "kahwa", an invigorating beverage made from roasted coffee fruits ground with animal fat.
For several centuries, coffee was roasted at home over an open fire or, more often, baked in ovens in flat pans. And by the way, it was mostly the task of children.
The first devices for roasting coffee appeared in the east in the 17th century. The cores were poured into a closed cylindrical space and placed on an open fire. A gripping area is attached to the outside to rotate the chamber and allow for a more even roast and mixing of the coffee.
The Industrial Revolution of the 19th century also revolutionized coffee roasting. The first commercial roasters began to be developed and produced in Europe and the USA. This was largely supported by the Coffee Purity Act. It made sure that the factories only sold pure coffee and no grain was added. Thus, the roaster gradually moved from home to production.
At the beginning of the 19th century, roasters looked like blacksmiths' shops: dangerous, hot, smoke and fire, very hard physical labor. The device of the first commercial roasters was very simple: a closed metal cylindrical drum was placed in an oven or open fire. Because wood or coal was used as fuel, the roasters overheated and could even explode. The worker could not see what was going on inside and could not control the roasting. To pour the coffee, it was necessary to remove the red-hot roaster from the fire. Roasters of that time faced the problem of how to extract and cool the roasted core. Therefore, the scorch of the American industrialist Jabes Burns, which appeared in 1864, became a real salvation. A special opening mechanism made it possible to pour the finished coffee without removing the roaster from the oven. Burns also placed a pair of screws inside the cylinder to mix the grain. Later, the roaster was equipped with a cooling tray. Hot grain was poured into a tray and cooled by air supplied by a fan below. These innovations have made the coffee roasting process more consistent in quality and less hazardous.
By the way, the Burns family became famous not only for the invention of new roasters, but also for the publishing business. One of Burns' sons founded the then-popular coffee industry magazine Spice Mill, and the other was scientific advisor to William Uckers' book All About Coffee. What Burnses wrote about coffee roasting in 1922 was quite interesting;
- If all coffees were the same, roasting would soon be automatic. But coffee, which varies from variety to variety in moisture, density and other properties, will confuse the operator until he or she learns to understand the grain. The key to understanding is constant practice in roasting. Therefore, the roaster should carefully observe, draw reasonable conclusions and remember exactly what he studied. Anyone can roast coffee, but only a few are truly good, and no one can roast coffee so well that there is no need to improve it.
Towards the end of the 19th century, manufacturers began experimenting with ways of introducing hot air into a drum cylinder. The task was to remove the fumes and gases formed during roasting and to provide fresh air to the roaster. The hood roaster was invented by the German industrialist Van Gulpen. The hood forced hot air through holes in the drum or from one end of the drum to the other. As a result, closed coffee roasting cylinders were replaced with ventilated ones. Van Gulpen is a co-founder of Emmericher Maschinenfabrik und Eisengießerei, which patented a horizontally rotating roasting drum in 1884.
was one of its founders. This technology and new air supply technology are of great importance in the development of the roasting equipment industry. In 1920, the factory produced the first roasting machine of the PROBAT brand and in 1959 it was renamed PROBAT Werke.
Generally, in the second half of the 19th century, roaster manufacturers experimented with heating and cooling sources, roasting drums and ventilation systems, and also developed a probe for sampling coffee during roasting. All these technologies are the basis of modern drum roasters.
Another qualitative change was the use of natural gas as fuel instead of wood or coal to heat the roasters, giving the core a smoky flavor. Electric roasters appeared at the beginning of the 20th century.
The first electric air or convection roaster was developed for display cases in 1926. In the 1950s, Lurgi introduced the Aerotherm roaster, which roasted coffee in hot air.tti. However, due to its design features, the machine was not suitable for commercial use: it was too small and required too much concentration from the roaster - it was always necessary to control the air flow so that the grain did not burst.
In the 1970s, chemical engineer Michael Sivetz developed the industrial convection roaster. Michael adapted the technology from the polyurethane production process in which magnesium granules are dried in a hot air chamber in one of the stages.
Convection roasters roast coffee approximately 50% faster than drum roasters. And the design is simpler: a burner or an electric heater, a blower and a roasting chamber. However, the specialist community still prefers drum roasters as they provide a better and more stable roast.
The modern coffee industry has a much better understanding of roasting and coffee chemistry. Accordingly, the design and equipment of roasting machines became more complex and perfect. Digital software has emerged to help monitor and analyze the roasting process.
How do roasters roast coffee?
There are three types of heat transfer used in roasting the coffee bean. These are conduction, convection and radiation.
Conduction, or thermal conductivity, is the transfer of heat from a warmer object to a cooler object. For example, you hold a cup of hot tea in your palms to warm your hands. The following operation occurs in the list. The drum is heated from a heat source - a gas burner or electric, the grain is loaded into a heated drum.
Convection is the transfer of heat energy through the movement of air. For example, you turn on a hot oven and feel hot air come in. In the roaster, the air heated by the burner passes through the coffee bean, transferring heat to it.
Emission or radiation, Energy is transferred in the form of waves or particles. Heat waves cause molecules on the surface of an object to move faster. The energy that produces heat is released. For example, radiation keeps you warm when you sit by the fire. Also, a heated roaster radiates heat.
While conduction and convection in a roaster can be controlled, radiation is still difficult for roasters to control.
All three types of energy work in modern roasters, but to varying degrees. Loring's new generation of convection roasters with the new drum, and especially the drum, use more convection energy to roast the coffee - up to 75-85% .
Chemical reactions in coffee during roasting.
Hundreds of chemical reactions take place during roasting of the coffee bean. Roasting destroys compounds, replaces them, and creates new ones. Here are three key reactions that give coffee beans its familiar taste.
Maillard reaction
In 1912, the French scientist and doctor Louis Camille Maillard published a scientific paper on the chemical reaction between amino acids and sugars during the heat treatment of food. The importance of the work was only realized after the Second World War, at the same time this reaction was called the Maillard reaction.
The Maillard reaction produces a brown crust and characteristic toasty flavors and aromas on steak or bread. Same with coffee. During the reaction, melanoidins are formed, which are responsible for the darkening of coffee beans. Melanoidins are important for body building and stable espresso crema. The recognizable bready/roasted flavor of coffee is also melanoidins. The Maillard reaction can also create other aromatic compounds - floral, fruity, caramel.
The spectrum and duration of the aroma compounds released during the reaction affect the flavor profile of the coffee. A short reaction can make the coffee more fruity, while a long reaction can add body.
Also, the Maillard reaction demonstrates the importance of sugar in green cereals. Sometimes even with good coffee in a pack there are light grains. This is immature and not enough sugar grains. When roasted, the lack of sugar does not trigger the desired reactions, hence the light color and flat taste.
Strecker reaction
Other names are Strecker degradation or decomposition. The process is named after German scientist Adolf Strecker, who discovered a method for obtaining amino acids from aldehydes and ketones.
During the Strecker reaction, amino acids interact with compounds formed during the Maillard reaction. As a result, aldehydes and ketones are formed, which are responsible for the different flavors and aromas we feel in coffee. For example fruit, citrus, flower, oil, chocolate.
Caramelization
At high temperatures, the complex sugars in the coffee bean break down into simpler, water-soluble sugars. These sugars, which we then feel in our drink – give taste and taste like caramel, burnt sugar or sweet flavors like almonds. Caramelization starts at about 170 C and continues until the end of roasting.