Rubasse Blog

Basic Coffee Roasting | Light Roast, Medium Roast & Medium-Dark Roast

884 | 2020-11-10

Basic Concepts of Roasting

Coffee is currently the second largest commodity after oil of the Global Futures and Options Volume, and one of the most popular beverages in the world today. In Taiwan, coffee is very easy to get in convenience stores, drink-shop chains, and many home-roasted coffee shops. We can say “All roads lead to coffee”. You can easily find the flavours belong to you in many places.

The 3 Keys to the Coffee Tastes

Except for the original taste of the raw coffee beans, roasting has a salient influence on the coffee tastes.

Coffee roasting can be roughly categorized into 5 stages:

  • Preheat: Preheat the roaster and set up the starting temperature which is called “charge temperature”.
  • Dehydration period: The water content is approximately 10-12% in the green bean. Water is the heat-conducting medium. With the rise of the temperature, the free water in the beans is evaporated and generate the gas inside.
  • Maillard Reaction: When the green beans turn from green to white and turn into tawny, and smell like the aroma of toast, the next is the so-called Maillard reaction and caramelisation. Maillard reaction refers to a series of reactions during heating, including the reducing of sugar and the protein/amino acid in the food, which produces a brown-black macromolecular substance, also known as a flavour compound.
  • Development period: The beans turn to darker brown and the temperature also increase to about 195℃. At this moment, we need to pay attention to the upcoming crack sounds. First crack is a reaction that the carbon dioxide and water in green beans expand by heating and the beans swell, which is also the key to the flavour and taste.
  • Discharge and cooling: When it meets your preference of roast level or temperature, you can discharge the beans for cooling. Cooling is the ultimate key to coffee roasting. Try to reduce the heat of the beans in as short a time as possible to lock the flavour to the temperature you decide as well as to the condition of the discharge.

Basic Coffee Roasting Terms

  • Bean temperature: the present temperature of the coffee bean surface measured by the thermometer.
  • Rate of Rise: Also known as ROR, it indicates the velocity of temperature increase which is influenced by the heat, airflow and rotation speed.
  • Dehydration water removal volume (optional hygrometer): The dehydrated amount of water from the beans after heating.
  • Wind temperature: The temperature of the hot air exhausting from the roasting chamber.
  • Differential pressure: The pressure difference between the roasting chamber and the outside of the roaster.
  • Turning point: When charging the beans, the temperature plummets until it reaches the timing, turning point, that the ROR turns into positive value from negative value.
  • First crack: The first time that the beans crack open after being heated, the third cracking sound can be taken as the start of the first crack.
  • First crack in intensity: When the beans start cracking in intensity in the middle of the first crack.
  • First crack in the tail end: the first crack is going to an end and the cracking sound tapers off.
  • Second crack: The beans are heated to reach the second time crack.

 

Roast levels and flavours

Before the roast, we need to understand that different roast levels will produce or emphasize on different flavours, for example, “light roast” will highlight the floral and fruit aromas, etc.; “medium roast” has a buttery, nutty fragrance; the medium-dark roast has a chocolate taste and a trace of foresty earth and floral herbs.


base on Coffee taster's flavor wheel

Rubasse Fully Automatic Infrared Roaster | Instructions for Beginners

This paragraph will introduce the basic roasting techniques so that you can quickly familiarise yourself with the operation of the Rubasse roaster.

It is very easy to get the hang of coffee roasting with Rubasse Infrared Fully Automatic Roaster. Rubasse utilises the short-wave infrared radiation to directly irradiate the beans to achieve the heating purpose through the radiation transmission technology. Compared with the other roasters, it is relatively simple because there will be no concerns about the uniformity and the uncooked issues. We just need to concentrate on the adjustments of the techniques.

All the control parameters and adjustment methods can be clearly seen on the operation interface. You can also refer to the basic profiles for copying and learning. All designs allow users to operate very intuitively. Therefore, when operating the roaster, the users will have sufficient time to make the corresponding reaction. It is perfectly suitable for beginners.

⤵ Basic instruction of Light Roast | First Crack in Intensity
⤵ Basic instruction of Medium Roast|First Crack in the Tail End
⤵ Basic instruction of Medium Dark Roast|Close to Second Crack

 


 

Light Roast | First Crack in Intensity

Generally, the lightly roasted coffee will mainly emphasize the bean’s distinctive floral and fruit aromas, lemon acidity, etc. to highlight the original flavour of the beans.

However, if the coffee has an unpleasant grassy and earthy taste, it means that the roast is too light, which is so-called “underdeveloped”.

The following is the roasting techniques of Rubasse Infrared Automatic Roaster. All the actions are made through the long-term observation and step-by-step adjustments by the users so that you can easily get the hang of roasting for the first time. (Taking the 300g batch roasting for example):

  1. Settings of parameters upon preheating:
    • Preheat temp.: 210℃
    • Charge time: 10 sec.
    • Initial power: 35%
    • Initial wind speed: 45%
    • Discharge time: 15 sec.
    • Cooling time: 200 sec.
    • Drum rotation speed: 40
    • Discharge temp.: 213℃
    • Unload time: 30 sec.
  2. After setting up, load the 300g green beans to the hopper.
  3. When the roaster reaches the preheat temp. (210℃), it will start to charge automatically.
  4. Turning point: After charging beans, the bean temperature will drop quickly to the turning point and then start to rise.
  5. Dehydration phase: The bean temperature rises to about 150℃ from the turning point.
    • “The initial settings can remain the same until the temperature reaches 150℃ and the ROR remains at 15℃-20℃ per minute.”
    • The bean colour will gradually change from green to white then to yellow again. When it turns to yellow, it is going to enter the Maillard Reaction.
  6. Maillard Reaction phase: From approximately 150℃ to 200℃.
    • “To adjust the power to around 23-25, the ROR will be at around 10-13 and the wind speed and the rotation speed can remain the same.”
    • During the time, it is undergoing Maillard Reaction and Caramelisation Reaction. The curve is going to become relatively steady and then the first crack will start.
    • With a hygrometer, you can observe the moisture has been greatly increasing.
  7. First crack: Starting from 195℃
    • “When the first crack starts, adjust the power to 15-18, maintain the ROR within 4-9, and then turn the wind speed to 75 to exhaust the silverskin. At the moment, the ROR will start dropping. Please note that do not let the ROR drop to a negative value.”
    • At about 195℃, if you listen carefully, you will hear the audible “pops”. Because of the small batch, the cracking sound will not be that loud. The third cracking sound can be taken as the start of the first crack. At the moment, the silverskin will greatly go off, and the bean colour will also change from yellow to dark brown; meanwhile, the dehydration and exothermic reactions of the beans will take place as well.
    • The end of the first crack also means the end of the dehydration and exothermic reactions. With a hygrometer, we can find that the moisture of beans has been evaporated.
  8. Unload: At about 213℃
    • If you want a light roast, unload the beans when the first crack is ongoing in intensity. At the point, the bean temperature is around 213℃.

Note: When it is finished, you can archive the roast profile and name it according to your preference.

 


 

Medium Roast | First Crack in the Tail End

Compared to light roast, the medium roast has more obvious caramelisation reaction which tends to highlight the notes of nut, butter, peanut, etc., and the sweetness will distinct. The previous light roast characteristics in flavour will become implicit, such as the floral aroma is not easily detected in the medium roast.

Note: If you already have the light roast profile, you can select the profile and go for the “fully automatic mode” until the first crack. Then, change it to “half automatic mode” and continue the roast till the beans are mediumly roasted.

The following is the roasting techniques of Rubasse Infrared Automatic Roaster. All the actions are made through the long-term observation and step-by-step adjustments by the users so that you can easily get the hang of roasting for the first time. (Taking the 300g batch roasting for example):

  1. Settings of parameters upon preheating:
    • Preheat temp.: 210℃
    • Charge time: 10 sec.
    • Initial power: 35%
    • Initial wind speed: 45%
    • Discharge time: 15 sec.
    • Cooling time: 200 sec.
    • Drum rotation speed: 40
    • Discharge temp.: 213℃
    • Unload time: 30 sec.
  2. After setting up, load the 300g green beans to the hopper.
  3. When the roaster reaches the preheat temp. (210℃), it will start to charge automatically.
  4. Turning point: After charging beans, the bean temperature will drop quickly to the turning point and then start to rise.
  5. Dehydration phase: The bean temperature rises to about 150℃ from the turning point.
    • “The initial settings can remain the same until the temperature reaches 150℃ and the ROR remains at 15℃-20℃ per minute.”
    • The bean colour will gradually change from green to white then to yellow again. When it turns to yellow, it is going to enter the Maillard Reaction.
  6. Maillard Reaction phase: From approximately 150℃ to 200℃.
    • “To adjust the power to around 23-25, the ROR will be at around 10-13 and the wind speed and the rotation speed can remain the same.”
    • During the time, it is undergoing Maillard Reaction and Caramelisation Reaction. The curve is going to become relatively steady and then the first crack will start.
    • With a hygrometer, you can observe the moisture has been greatly increasing.
  7. First crack: Starting from 195℃
    • “When the first crack starts, adjust the power to 15-18, maintain the ROR within 4-9, and then turn the wind speed to 75 to exhaust the silverskin. At the moment, the ROR will start dropping. Please note that do not let the ROR drop to a negative value.”
    • At about 195℃, if you listen carefully, you will hear the audible “pops”. Because of the small batch, the cracking sound will not be that loud. The third cracking sound can be taken as the start of the first crack. At the moment, the silverskin will greatly go off, and the bean colour will also change from yellow to dark brown; meanwhile, the dehydration and exothermic reactions of the beans will take place as well.
    • The end of the first crack also means the end of the dehydration and exothermic reactions. With a hygrometer, we can find that the moisture of beans has been evaporated.
  8. First crack in the tail end: at about 213℃
    • “When it closes to the tail end of the first crack, adjust the power to the range of 24-28 and maintain the ROR within the range of 4-6.”
  9. End of the first crack: At around 216℃
    • “Adjust the power to 20-24, keep the ROR within 4-6, decrease the wind speed to 55 and keep the rotation speed unchanged.”
    • The moisture in the beans is low. If continue roasting with the power at 24-28, the ROR will go up crazily which will condense the development time.
  10. Unload: At around 218℃~220℃
    • If you want your beans mediumly roasted, discharge the beans at 218℃~220℃.

Note: When it is finished, you can archive the roast profile and name it according to your preference for future reference.

 


 

Medium Dark Roast | Close to Second Crack

NOTE: As for the taste and healthiness, dark roast is not the best choice!

Dark roast is Taiwanese’ most familiar coffee flavour. Medium-dark roast highlights the note of chocolate and spices and woody scents. Mandheling is the most common item of the medium-dark roast, It has a charming woody and spicy tone with a low level of sour and bitterness which is the typical taste of Mandheling and also the characteristic of the medium-dark roast.

Note: If you already have the medium roast profile, you can select the profile and go for the “fully automatic mode” until the end of the first crack. Then, change it to “half automatic mode” and continue until the medium-dark roast.

Below is the roasting techniques of Rubasse Infrared Automatic Roaster. All the actions are made through the long-term observation and step-by-step adjustments by the users so that you can easily get the hang of roasting for the first time. (Taking the 300g batch roasting for example):

  1. Settings of parameters upon preheating:
    • Preheat temp.: 210℃
    • Charge time: 10 sec.
    • Initial power: 35%
    • Initial wind speed: 45%
    • Discharge time: 15 sec.
    • Cooling time: 200 sec.
    • Drum rotation speed: 40
    • Discharge temp.: 213℃
    • Unload time: 30 sec.
  2. After setting up, load the 300g green beans to the hopper.
  3. When the roaster reaches the preheat temp. (210℃), it will start to charge automatically.
  4. Turning point: After charging beans, the bean temperature will drop quickly to the turning point and then start to rise.
  5. Dehydration phase: The bean temperature rises to about 150℃ from the turning point.
    • “The initial settings can remain the same until the temperature reaches 150℃ and the ROR remains at 15℃-20℃ per minute.”
    • The bean colour will gradually change from green to white then to yellow again. When it turns to yellow, it is going to enter the Maillard Reaction.
  6. Maillard Reaction phase: From approximately 150℃ to 200℃.
    • “To adjust the power to around 23-25, the ROR will be at around 10-13 and the wind speed and the rotation speed can remain the same.”
    • During the time, it is undergoing Maillard Reaction and Caramelisation Reaction. The curve is going to become relatively steady and then the first crack will start.
    • With a hygrometer, you can observe the moisture has been greatly increasing.
  7. First crack: Starting from 195℃
    • “When the first crack starts, adjust the power to 15-18, maintain the ROR within 4-9, and then turn the wind speed to 75 to exhaust the silverskin. At the moment, the ROR will start dropping. Please note that do not let the ROR drop to a negative value.”
    • At about 195℃, if you listen carefully, you will hear the audible “pops”. Because of the small batch, the cracking sound will not be that loud. The third cracking sound can be taken as the start of the first crack. At the moment, the silverskin will greatly go off, and the bean colour will also change from yellow to dark brown; meanwhile, the dehydration and exothermic reactions of the beans will take place as well.
    • The end of the first crack also means the end of the dehydration and exothermic reactions. With a hygrometer, we can find that the moisture of beans has been evaporated.
  8. First crack in the tail end: at about 213℃
    • “When it closes to the tail end of the first crack, adjust the power to the range of 24-28 and maintain the ROR within the range of 4-6.”
  9. End of the first crack: At around 216℃
    • “Adjust the power to 20-24, keep the ROR within 4-6, decrease the wind speed to 55 and keep the rotation speed unchanged.”
    • The moisture in the beans is low. If continue roasting with the power at 24-28, the ROR will go up crazily which will condense the development time.
  10. Enter into the medium-dark roast stage: At approximately 220℃
    • “At the moment, adjust the power to 14-18 and maintain the ROR within 4-6.”
  11. Attention: 225℃
    • “When the beam temperature reaches 225℃, turn the wind speed to 70.”
    • Here comes the second crack.
  12. Unload: At around 228℃~230℃
    • When it is approaching 228℃, listen carefully to the popping sound of the second crack. Compared with the first crack, it is relatively quieter like the sound of firecrackers.
    • Unload at around 228~230℃ if you want to touch the second crack.

Note: When it is finished, you can archive the roast profile and name it according to your preference for future reference.

Suggestion on the size of batch and preheat parameters

  • 1000g: Power 50, wind speed 55 and rotation speed 55 upon charging the beans
  • 2000g: Power 60, wind speed 65 and rotation speed 65 upon charging the beans
  • 3000g: Power 70, wind speed 75 and rotation speed 80 upon charging the beans 

Coffee taster's flavor wheel 

/Photo by SCAA