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ONIBUS Basic Knowledge of Roasting

10 Basics to Start Roasting

There are several important points and phases for roasting.
I put them together a little bit.

There are input temperatures, turning points, first cracks, and end temperatures, but this time I'd like to explain them.

(1) Input temperature

How many times do you want to put raw beans into the roasting machine?

It is necessary to decide to think about the whole process of roasting, such as the temperature zone of the middle of the roasting and the temperature of the end. (OniBUS 190-210° ends around 205°)

The temperature of raw beans before roasting affects the temperature inside the kettle when it is introduced into the roasting machine. How many times did you keep the raw beans? In order to control it, it is important to keep the raw bean temperature constant at the time of input.

Turning point

When the raw beans are poured into the roaster, the heat inside the roasting machine falls once and begins to rise again. The point where it begins to rise is called a turning point (midpoint, bottom, turning point). The temperature of the bottom changes whether the burner is ignited before this turning point or the firepower is strengthened after the turning point. We will adjust the fire power in the future thinking about how to raise the temperature from the turning point.


Gas pressure at input 2 → 50 seconds later Gas pressure 7

(3) Roast Curve and RoR (Rate of Rise)

A graph that connects a roasting machine and a personal computer via USB to visualize the temperature rise is called a roast curve.

The shape of the roast curve varies depending on the burner's thermal adjustment, airflow, raw bean moisture levels, and environmental temperature. We will make a roasting recipe based on how this curve affects beans.

RoR tells us about the rate of increase in temperature and shows how the temperature is progressing in the kettle. RoR is used to quickly understand how temperatures go. You can relative lyse the roast curve and RoR, and you can control the roast well to create the profile you want.


(1) First Crack

As the roast progresses, the coffee loses moisture and many scientific changes occur, including the Maillard reaction. When the bean becomes a constant temperature (around 195°C in ONIBUS) water vapor and carbon dioxide are generated along the crack of the bean, but the pressure rises and it releases it to the outside. At that time, cracking and cracking sound occurs. This is called one haze.

(2) End temperature

The time from 1 haze to the end of roasting is called development time. The degree of roasting changes whether the temperature of this roasting end is made how many times, and the temperature ends together with what kind of firepower.

(3) Moisture ross, roast color

The change in moisture before and after roasting, and the color of roasted beans are expressed numerically.

Moisture Ross Formula

Post-roasting bean weight / weight of raw beans -1

Example 3000g / 3400g -1= minus 11.7%

You can see that the moisture decreased by 11.7% from before the roast.

The color of roasted beans is quantified by L values. ONIBUS COFFEE uses roast color analyzer Lighttells CM-100 to measure the roast color.

By managing moisture loss and roast color, roasting is more uniform.

(4) Atmospheric temperature, environment

Roasting also affects beans during roasting by spreading heat by radiant heat in the roasting machine. Especially in summer and winter in Japan, the temperature read by the thermometer of the roasting machine is different from the effect that roasting actually has. Even if you give the same calories, ror and roast curves may be different from the previous value.

(5) Drying phase

This phase is the phase of preparation before roasting begins and the moisture in the beans evaporates and a scientific reaction begins. It is very important to evaporate moisture at the appropriate temperature.

(6) Maillard Reaction Phase

The Maillard reaction is a scientific reaction consisting of dehydration of sugar by heating. It reacts amino acids and produces melanoidin, which causes coffee browning.

The Maillard reaction phase is assumed to give the flavor of the coffee complexity and body.

(7) Development Phase

The coffee at this time is very brittle and delicate, and requires delicate thermal adjustment.

In general, the body increases when this time is taken for a long time, and the acid decomposes. It is also a phase where it is very complex and various scientific reactions occur.

For example, caramelization of sucrose and other pyrolysis, carbonization, Maillard reaction, stecker decomposition, decomposition and generation of organic acids.

At last

These reactions start at different temperatures, and change at different times in the drum at different times. Because each individual has a different coffee structure, the reactions are overlapping and progress, and it is very complex. You should not analyze them alone. All the points and phases are united and they influence each other. It is important for roasters to predict these reactions and accumulate data and experience so that they can pay attention to the aroma and color of the beans and control the entire roasting process.


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