Design of coffee roaster with controlled temperature system to maintain the sustainability of coffee roasting process

One of the most important process in producing coffee beverage is the roasting stage. Nowadays, roasting process is done using mechanic process by giving high temperature to coffee beans. However, the temperature is not controlled and the capacity tend too high or low, expensive and need a qualified coffee roaster to do this stage, which is not suitable for small and micro bussiness. This research aimed to answer those problems by designing a roasting machine that could control the temperature with a capacity of 4 kg per process. Result showed that the roasting machine could roast the coffee bean in 52 minutes to achieve the medium to dark roast level, and it is suitable for the small and micro bussiness according to the roasting profile and from the economic analysis this machine is feasible. Moreover, this coffee roaster is energy efficient and could provide a better livelihood for the user to produce the roasted beans even with no roasting experience.


Introduction
Coffee become one of the mostly drink beverage in the world.Before the coffee is consumed, it has been through a long process from cultivating, harvesting, sorting, pulping, fermentating, washing, drying, hulling, roasting and grinding.Each step of those process will influence the flavor of the coffee, including the roasting process.Roasting process is giving such a temperature to coffee beans [1] until the coffee is ready to be served to the grinding process.Before the roasting process, the roasters must make sure that the water content of the coffee is maximum 12.5% [2].Roasting brings out the coffee flavor that is locked inside the green beans.Along the roasting process, there will be several matter that is replaced by another, for example the volatile compounds is existed after being roasted while the other concetration such as trigonelline and chlorogenic acid is decreasing.
In coffee roasting process there are three levels namely light roast, medium roast and dark roast, and each level has its market.The roasting temperature and time used to gain these levels also different.In light roast level the temperature of 190-195 o C could be used, then in the medium roast level the temperature used is in the range of 200-210 o C and in the dark roast level the temperature used is above 210 o C [3].The temperature used in roasting coffee is depend on the roaster type, but the maximm temperature that could be used generally vary from 210-240 o C [4].However, the time used will also be influenced by the amount of coffee that is processed.All the treatment will influence the parameter such as the yield and the coffee flavor.
Nowadays, there are several types of coffee roaster that diverse from the capacity, heating process, roasting process, etc.For coffee industry the high capacity of coffee roasting process starting from 10 kg per process to 40 kg per process could be found [1].However, it is not suitable with the needs of small and micro bussiness industry, that can be found now in every village which has coffee plantation.The capacity will influence the cost per process, the price of coffee roaster and certainly the availability of the raw material must be noticed.This study aimed to design a rotary type coffee roaster with burner as the heat source and controlled temperature with capacity per process of 4 kg which is suitable for a small and micro bussiness industries to provide a better livelihoods for the coffee farmers in villages.

Material and Methods
This study showed the design process of the coffee roaster, up through the testing of the coffee roaster to the yield of the roasted coffee.The materials used in this study were stainless steel tube, perforated stainless steel pipe, electric motor, burner, gear, chain, pulley, v-belt, bearing, reducer, iron elbow, bolts and nuts.Before fabricating the roasting machine, the design and calculation about the materials that will be used were conducted.The hopper and the rotary tube were designed to accomodate 4 kg of coffee beans for both arabica and robusta coffee.Moreover, from calculation of the amount force that is required to rotate the rotary tube with 4 kg load, it shows that ¼ HP of electic motor is required to rotate it during the roasting process at the speed of 17.5 rpm.After that, this study continued with fabrication and the testing stage using 4 kg of green coffee bean followed with the evaluation of the process by calculating the time used per process, the yield and feasibility testing by the economical analysis.

Result and Discussion
The designed coffee roaster (Figure 1) consist of several important parts, such as 4 kg capacity of hopper (Figure 2), roasting tube (Figure 3), output channel (Figure 4), and temperature controller using thermocouple and thermostat.The roasting process is conducted inside the roasting tube (Figure 3) with a controlled temperature of 180 o C. In coffee roasting practice the temperature will be fluctuated according to the condition inside the roaster tube and the heat source.In this designed roaster, firstly the temperature is set to 200 o C which took about ± 5 minutes, this condition is conducted to achieve a high turning point of about ± 70 o C.After that, the temperature inside will rise slowly untill it achieve 180 o C in ±47 minutes and the roasting process is done.Infact, the roasting time is influenced by the roasting capacity, for example in [5] a coffee roaster with18 kg per process needs 78 minutes with temperature of 205 o C. The roaster system is controlled by the thermostat that is connected to the thermocouple that is placed inside the roaster tube.In this machine, there are 3 layers of tube, the first one is the outer layer that we could see from outside, then the second layer, where the rockwool is place to hold the heat inside the roaster tube, and the third layer inside where the coffee beans and the thermocouple are placed and this layer also called as the rotary tube.Moreover, the heat is produced by a burner.It does not take along time roasting coffee beans using this machine even the capacity is 4 kg per batch compared to the research which roast coffee beans with capacity under 1 kg [6], which showed that the roasting process is conducted in 65 minutes for roasting 300 grams of coffee bean.
Along the roasting process using the designed coffee roaster (Figure 4), the roasting tube is keep rotating with the rotation speed of 17.5 rpm.This rotation was gained from the 0.25 HP electric motor then transmitted using pulley (1.5 inch and 3 inch) and v-belt then reduce by speed reduce and trasmitted to the rotary tube.While roasting, the green coffee beans experience several stages such as drying, yellowing, first crack, development and developed stage.In this designed coffee roaster, the yellowing stage is achieved in ± 25 minutes after the machine is turned on. in this stage, most of the water inside the beans are removed and the coffee is starting to brown slightly then at the first crack stage the coffee starts to pop and expand in size due to the build up of gas pressure inside the bean, then follows with the development stage where the beans are increasingly smooth from the outside and the flavor as the combination of taste and aroma is increasingly could be detected pleasantly.On the other hand, chemically, there are several shifts experience while the coffee is being roasted, such as when the beans temperature reach 130 o C, the sucrose inside the bean is caramelized so that the beans' color begin to brown and swell.Moreover, at higher temperature > 160 o C, several reactions both exothermic and endothermic take place,

Figure 1 .
Figure 1.Coffee roaster with controlled temperature

Figure 2 .
Figure 2. Details of the hopper design (all size is in cm)

Figure 3 .
Figure 3. Details of the roasting tube (all size is in cm)

Figure 4 .
Figure 4. Details of output channel (all size is in cm)