Coffee roasting technique – How to roast delicious coffee at home

Coffee is increasingly popular, as a drink that helps us feel more full of life. Coffee is easy to buy and ubiquitous. However, at the bar, the barista creates mass coffee flavors that cater to most tastes. To experiment, sometimes you want to learn how to roast coffee and roast yourself a batch of coffee at home. If so, the following article is for you.

Overview of the process of transforming coffee beans when roasting

  • Coffee beans will change color and flavor drastically during roasting. Because when roasting, the moisture in the coffee will evaporate, making the coffee beans dry and expand.
  • During this process, some natural sugars are converted into CO2. While others are caramelized into complex flavors in coffee. When the process is complete, green coffee beans will turn into brown coffee beans that are about 18-23% lighter, while the size will be 50 to 100% larger.
  • As soon as the roasting process is complete, the coffee will have a clear aroma.
Coffee beans change when roasted
When roasting coffee will change the chemical composition of coffee to create flavor and taste.

10 stages of coffee bean transformation when roasting

  1. Green Coffee Beans: Coffee beans will retain their original essence, even after heating has begun.
  2. Turning Yellow: The color of the beans will become slightly yellow and will have a grassy smell.
  3. Evaporation stage: Steam will rise from the coffee beans because the temperature has increased inside the beans.
  4. First Crack (Cinnamon Roast) – First crack: At this point we begin the actual roasting process. The sugar inside the coffee beans is caramelized. You will now hear a cracking sound, like the sound of popcorn popping.
  5. City Roast: After the first crack, the beans have reached the City Roast stage, the minimum roast level to be able to brew coffee.
  6. City Plus Roast: At this point, the beans swell. This is a roast level commonly used for many brewing methods.
  7. Full City Roast: After the City Plus phase is Full City. At this level, the coffee beans will prepare to generate the second crack sound.
  8. Second Crack (Full City Plus Roast): When heated to this temperature, the coffee beans will make a second crack. At this stage, the coffee flavor will reach its maximum.
  9. Dark Roast (French Roast): At this stage, the sugar in the coffee will be burned off. However, the taste remains. This is the maximum limit of the roasting process and gives the best flavor.
  10. Burning: At this stage, the smell of the seeds is like being burned.

Coffee roasting levels

In the specific coffee roasting process you can hardly observe all 10 stages as described above. To easily control the desired coffee taste when roasting coffee, you need to know the roasting levels as below. The stages are Light, Medium, Medium-Dark and Dark Roast.

Change the color of coffee beans when roasting
Coffee beans change color during roasting.

Light Roast

To achieve a light roast – Light Roast, the internal temperature during roasting should be between 356-401°F. Light Roast can be called Light city, Half city, and Cinnamon Roast. But whatever the name, they tend to fall around the beginning of the first crack. At this point, the surface of the beans is still dry and the beans can be quite thick and hard.

You can choose this roast if you prefer coffee with higher acidity or a brighter color. At this roast level, your coffee will have a lingering mild sour taste.

Medium Roast

For medium roasts – Medium Roast, including City and City plus, you can set the temperature to 410-428°F. Coffee beans will still have a relatively dry surface but are more distinct from the original green beans. This roast occurs from the middle to the end of the first crack.

This roast is more popular than Light Roast thanks to its medium acidity. The cup of coffee is now less sour and begins to have a stronger coffee flavor.

Medium Dark Roast 

The roast is medium dark when the temperature is between 437°F – 446°F. You may start to notice patches of oil when the beans have a second crack. This stage can be called by other names: Full-City, Full-City+, Vienna Roast. This is the time when the flavors start to stand out more for the best cup of coffee.

Dark Roast

Finally, French Roast, Italian Roast, and Espresso Roast are all considered dark roasts. Roasting temperature is about 464°F. You need to keep the temperature below 482°F to avoid turning the beans into charcoal. At this time, the cup of coffee has a strong bitter taste.

Instructions on how to roast delicious coffee at home

After mastering the knowledge of coffee roasting techniques and coffee roasting levels as we have presented. You can roast yourself a batch of coffee at home by following these steps.

Step 1. Buy unroasted green coffee beans

You can buy a few pounds of unroasted coffee at coffee shops or online. However, if you are roasting coffee for the first time, you probably have no experience with the type of coffee you like. Therefore, it is necessary to buy a moderate amount for testing. Then you can buy more if you like the coffee.

green coffee beans
You need to prepare quality coffee beans for the roasting process.

Step 2. Prepare the coffee roaster

Currently on the market there are small coffee roasters that are suitable for roasting coffee at home. However, the price is still quite high, the cheapest one is more than 6 million VND (legendary Lysander). You can also build yourself a similar machine with the cost of materials about 2-3 million.

Lysander coffee roaster
If you are a coffee fanatic, you can choose to buy yourself the legendary Lysander machine.

If roasting coffee with a Lysander machine, or a homemade roaster, you need to prepare a timer and travel mini gas stove.

Travel gas stove roasting coffee
Remember to equip the switch and mini gas tank when you buy this type of gas stove.

Step 3. Start roasting the coffee

Roasting time

Usually when roasting coffee with manual roasters at home, it is not possible to measure the internal temperature of the coffee beans to finish the roast. However, you can rely on the crack to prepare the end of the roast. Specifically, the roasting steps are as follows:

  • It is necessary to preheat the roasting cage for about 6-7 minutes before placing the coffee in the roasting cage. You can check by inserting your finger in the center of the roasting cage. If you feel a burning sensation after 3-5 seconds, then the temperature of the roasting cage is enough to put green coffee in.
  • Adjust the gas so that the first explosion (Fist Crack) falls around 8:30. You should experiment a few times with low-priced coffee to gain experience adjusting the amount of gas so that the noise occurs at this time.
  • Immediately after Fist Crack, reduce heat and extend roasting to 2:00 – 2:30: Suitable for Pour over.
  • Roast until 4:00 – 4:30 after the first bang: Suitable for Syphon, French Press.
  • Roast until 5:00-6:00 occurs the second explosion (Second Crack).
  • Roast more 1:15 to 2:30 after the second bang: Suitable for mixing filter, Espresso. Depending on the taste, prolong the roasting time accordingly.
Roasting coffee with Lysander machine
Roast coffee with Lysander machine at home.

Note when roasting coffee:

  • Depending on the type of coffee, depending on the preliminary processing method, the time for the explosion may vary slightly.
  • For Robusta coffee, it is difficult to notice the first explosion. In contrast, the first explosion occurs very clearly in Arabica coffee.
  • You can also end the roast based on the color scale below. If you are familiar with roasting, you can notice the correlation between roasting time and color scale very clearly.
color of coffee beans when roasted
Change in color of coffee beans when roasted.

Graph of roasting heat:

Dark green line:  Accumulated temperature inside the coffee bean. This temperature is measured through a thermometer placed in the roasting cage. Therefore, from 0:00 to 1:20, the temperature indicated on the thermometer decreases due to the lower coffee temperature, which reduces the temperature of the roasting cage. Time 1:20 is called the heat recovery point. When the coffee was roasted until 8:30, the first explosion occurred.

Light green line: ROR line, indicating the heating rate during roasting. For home roasting, you can rely on the ROR line to reduce the heat towards the end of the roast. The truth is that it is very difficult to do properly.

Heat graph of roast
Heat graph of roasting batch (refer).

Step 4. Finish roasting

Depending on the purpose of roasting, you can end the batch at the appropriate time as described. You can study the flavor variation of coffee by roast level like the graph below to decide when to finish roasting.

Coffee flavor changes with roasting temperature
Coffee flavor varies with the degree of roasting (temperature).
  • Acidity: Acidity
  • Flavors: Flavors
  • Body: Physical
  • Sweetness: Sweetness
  • Roast Flavor: Bitter (literally translated :))

Step 5. Cool down the coffee beans after roasting

Once you’re satisfied with the roast level, it’s time to take out the coffee. You need to use a blower to remove the silk skin and cool the coffee quickly. Usually the cooling time is shorter than 5 minutes to avoid salting.

Step 6. Storing and using coffee after roasting

Coffee after roasting, there is a lot of CO2 released as they break down the grain structure in the first 24 hours. Therefore, as soon as roasting is complete, if you pack it right away, the coffee bag will swell, causing the seam to burst. However, if the coffee is left out for 24 hours, the coffee will lose its characteristic aroma. Therefore, it is best to pack it with packages with a one-way valve so that the inside air escapes, the outside air cannot enter.

You should store coffee in the form of beans. When making new coffee, grind the beans into a powder. This will preserve the full flavor of the coffee.

So you have mastered the basic knowledge about the transformation of coffee beans when roasting, how to roast coffee at home. Maybe when you roast for the first time, your batch of coffee is not as expected. Persevere to test a few roasts, you will draw your own experience. Gradually, you will reach the required level of roasting. Good luck.

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