Roasting techniques and factors affecting the roasting batch quality

Roasting is similar to cooking. It requires roasters to understand the basic biochemical factors and work on their own to characterize products. After a period of research, testing, and application, Vero hopes to show you the clearest view of the technical process for a standard batch of coffee.

Requirements: You have to use your ears to hear, your nose to smell and your eyes to observe colors. Coffee roasting is divided into three main phases: drying, Maillard reaction, and the final.

I. Drying phase: from room temperature to about 160 degrees Celcius

Input materials are so important that they must meet the standard with correct humidity. The first step is to heat the roasting drum. After the drum's temperature reaches 170-220 degrees Celcius, start filling it with coffee beans. The roasting drum heat drops quickly and then rises to about 155-160 degrees Celsius. This stage is the phase of evaporation and the beans change from green to pale yellow. The heating process can go 10-15 degrees Celcius per minute.

II. The Maillard reaction phase is divided into two small phases

1. The precursor dissection phase: from 160 to 185 degrees Celsius

After the water has been evaporated out, the coffee beans begin to dissociate metabolic to create catalyst and precursor for the Maillard reaction. The heating process is about 5-100 degrees Celsius per minute. During this stage, the beans odor the smell of grass, straw, and wood. Their color changes from pale yellow to gradually darkening. The outer velamen peel off, so it is necessary to absorb those velamen thoroughly.

2. Maillard reaction phase: from 185 to 200 degrees Celsius

This stage is extremely important in the aroma of coffee. It is a combination of sugar and amino acids in the coffee bean and the end product result is melanoidin with a dark brown color. The heating process reaches 3-50 degrees Celsius per minute. Take note: The aroma begins to appear when the combination of sugar and amino acids in the Maillard reaction occurs, the coffee beans turn brown due to the caramelization, and smoke starts rising.

III. The final phase: from 200 to 240 degrees Celsius

Depending on the flavor and brewing method, the roaster will stop to produce the desired product (see roasting chart). Take note, the roaster begins to observe and smell the aroma escaping to make the decision. There are 9 different levels of roasting as below.

1. First crack (Cinnamon level): The heat of 200 - 210 degrees Celsius leads coffee beans to emit increasingly fragmented explosions. The size and color of coffee beans are changed with alternating yellow-brown copper veins. The smoke was emitted more, the chemical reactions increase, creating many attractive aromas such as malt, toast, or honey. If you stop roasting at this stage, you will have a Cinnamon level coffee with a very sour taste but a rich and original flavor of the coffee bean.

2. First cracking stop: At the heat from 210 degrees Celsius, coffee beans start to stop cracking and continue to collect heat. The strong caramelization reaction continues, the coffee beans turn brown rapidly and emit a rich aroma and a lot of smoke. The scent can spread strongly outside the roasting area, making viewers ecstatic. The coffee beans are still very sour, the aroma is rich but the smell of roasted coffee beans has gradually appeared. If we stop at this stage, we have City level products.

3. Recovery period with 215 - 220 degrees Celsius: If we prolong the cracking phase, the coffee beans will brown more, their surfaces stretch beautifully with no wrinkles. The taste is much stronger. If we stop at this level, we have City + level products.

4. 220 - 225 degrees Celsius phase: The coffee beans will crack again and brown more, the aroma is sweeter gradually, and the sour taste decreases significantly. If we stop at this level, we have a Full city level product. Personally, this stage is the most balanced, the coffee bean will show its optimal qualities. However, it is difficult to determine this phase because each type of coffee grown at different heights and caregivers will have a different grain structure so that cracking times are not the same.

5. Second cracking at 225 - 227 degrees Celsius: The result of this phase is Full City + level products with less sour flavor and more caramelization.

6. Second cracking at 227 - 230 degrees Celsius: About 30-45 seconds after the second cracking, we have Vienna-style coffee whose original flavor has gradually faded and replaced by roasted flavor.

7. 230 - 235 degrees Celsius phase: About 50-60 seconds after the second cracking, we have French-style coffee whose sugar is completely caramelized.

8. 235 - 245 degrees Celsius phase: Finishing the second cracking, the coffee beans turn over 25% of the coal, the main flavors are smoke, coal, and burning. We have an Italian-style coffee.

After roasting, the beans will be cooled down quickly to prevent the beans from the self-roasting process leading to unwanted end products. Furthermore, the long cooling time will partly remove the flavor of the coffee.