Working Principle Of Coffee Roaster

Vietnamese Coffee Exporter

Working Principle Of Coffee Roaster: How can roasters ripen coffee beans evenly? What is the principle of Coffee Roaster? Understanding the principles of coffee roasters will help coffee roasters understand and be more proactive in the process of ripening coffee.

And the heat transfer mechanism is the most important, especially for any coffee roaster. Each coffee roaster will have different heat transfer mechanisms.

Convection heat, transfer heat, and radiative heat – Working Principle Of Coffee Roaster

– Traditional roaster is a roaster with a roasting cage that comes into direct contact with fire, first roasting the coffee beans with convection heat and then the transmission heat. The heat radiated from the roaster and the coffee beans themselves are also part of the coffee’s primary roasting process.


– Indirect roaster is a roaster with a roasting cage away from the heat source, ensuring that the roasting cage is not overheated. Convection heat plays a significant role in the heat transfer process for roasting coffee.

– Pipe roaster is a roaster without a roasting cage. Coffee is roasted with hot air blowing into the roasting tube at high speed, making the coffee beans fly, absorb heat and ripen.

These circulating roasters attract and recover difficult to discharge during roasting. Both of these roasters are designed to roast coffee entirely with convection heat.

In the first roasting stage, the roasting cage temperature will drop suddenly when the coffee beans have room temperature (about 37).oC) are put into the machine. In the first few minutes of the traditional cage roasting batch, the role of heat transmitted into the coffee beans from the roasting cage is evident.

Meanwhile, the temperature in the roasting enclosure will start to rise after it has slipped in the early stages slowly, convection heat will begin to play its role. For this type of machine, the roasting cage acts as a “heat cage” to ripen the coffee in the early stages of the roasting batch.

Convection heat roasters often need to measure the heat more significantly to get the required amount of heat in the early stages of roasting and offset the amount of heat heating the roasting cage.

Heat transfer process and temperature variation

About two-thirds of the first time, the roasting process is heat capture, which means that the beans will absorb energy, and the heat will be transmitted from the outside into the coffee beans. The temperature variation, or “temperature difference” inside the coffee bean, depends entirely on the performance of the heat transfer.

Simply put, the greater the temperature amplitude, the faster the temperature inside the coffee beans increases. The temperature range in the early stages is estimated at 50oC, peak at that point or maybe slightly higher; this margin will gradually decrease as roasting continues.

In other words, after the first few minutes of the roasting batch, the temperature in the core of the coffee bean is slowly on par with the surface temperature of the grain. The temperature amplitude is usually higher when roasted quickly and lower when roasted slowly.

Heat and heat transfer in coffee beans

The heat transfer mechanism and heat transmission capacity in coffee roasters play an essential role in determining the quality of coffee beans after roasting. Therefore, coffee roasters often carefully consider choosing a roaster with the correct heat.

In the early stages of the outermost layer of the coffee bean, steam begins to evaporate, forming a “layer of steam” that enters the inside of the grain core. The cellulose structure in the coffee beans is cooled, retaining steam inside the grain core. When the steam chamber structures are heated, the pressure increases the particle structure.

Heat and humidity transfer

The humidity of the roasting environment and the moisture in the coffee beans affect the heat transfer when roasting coffee. After the stagnation of the early-stage temperature, the humidity inside the roasting cage will increase the heat transfer process to release the amount of water in the coffee beans.

The amount of steam contained in the grain directly affects the coffee roasting process. Large amounts of smoke and heat transmission will have three main effects on the coffee beans.

– Increased heat transfer capacity because moisture increases heat transmission in coffee beans Increase the amount of energy heat, which means that more heat must be used for the same particle weight. More steam is released from the coffee beans, limiting the ability to transfer heat into the core of the grain.

Working Principle Of Coffee Roaster

The final impact is that the temperature in the moist grain will rise more slowly in the dry grain. Therefore, roasters must adjust the temperature properly by heating more extensively when roasting sticky grains and adjusting the temperature accordingly when roasting dry seeds.

Each coffee roaster will be designed according to its own unique operating principles. To achieve the best quality when roasting coffee, roasters need to know the coffee roasting mechanism of the machine they use to master the operation process, Control it.

Source: Working Principle Of Coffee Roaster

More: Learn About Industrial Coffee Roasters 

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