Coffee Knowledge | How to read the roasting curve during the roasting process?

Each bean has a corresponding roasting curve, so what does this roasting curve mean? How does it relate to what happens in our roasting oven?

A baking graph is a description of basic data. Once you know what the lines and points mean, they can help you improve your baking, solve problems, and repeat results.

Bean temperature (blue) and RoR (red) curves.

The curve drops when the beans are added

The first point of the blue curve refers to the bean temperature when the beans are put in. This temperature refers to the internal temperature of the roasting drum when the beans are put in.

When you put the beans into the roaster, you will see the temperature drop dramatically. However, this is not because the temperature of the beans is dropping. What you are actually seeing is the temperature change recorded by the roaster's bean probe.

The probes themselves don't actually measure the temperature of the beans, they only register the temperature of the beans in the drum and thus give an indication of the temperature of the beans.

In fact, the boiler is already heated before the beans enter it. The sudden addition of green beans will cause the heat energy to decrease, thus lowering the temperature read by the probe. So the curve will begin to show a downward trend.

Temperature recovery point

After the beans enter the boiler, they will immediately absorb heat, and the boiler temperature will drop suddenly. Then at a certain point in time, the temperature begins to rise. This turning point is the temperature recovery point of the beans.

Curved upward slope

The beans slowly lose moisture but continue to heat up at a variable rate, called the Rate of Rising (RoR).

The factors that affect the heating rate depend on many factors, including the quality of the coffee beans, the temperature of the beans, the moisture content, the processing method of the beans, etc.

The angle of the rising slope of the curve is related to RoR: the higher the rate, the higher the temperature the beans reach per time, and the steeper the curve.

Dehydration period

The upward slope of the curve will produce some reaction during baking .

Usually a few minutes after the return to temperature, the coffee beans will lose enough moisture and begin to show physical reactions. The beans begin to change from the green color of raw beans to yellow. This period can be called the dehydration period of the beans, but to be precise, the dehydration state of the beans during the roasting process will continue until the end of the roasting.

Maillard reaction process

When the temperature of the beans reaches 150°C, the Maillard reaction occurs. The carbohydrates and amino acids in the beans react due to heat, causing changes in color and flavor, which is also an important stage in the development of coffee aroma.

Hundreds of aromatic substances are produced during this reaction. During the coffee roasting process, the Maillard reaction begins when the color of the beans begins to turn yellow and then brown after dehydration is completed. The reaction will not stop until the end of the roasting and the beans are completely cooled.

Caramelization reaction

Coffee beans undergo caramelization at 170°C, which is exactly the melting point of sucrose (185°C) and the temperature of the first crack stage when roasting coffee beans.

The caramelization reaction produces dehydration products of sugar, the formation of caramel, color and aromatic substances, and this stage will contribute to the development of sweetness in the coffee beans.

The baking curve tends to be flat

A burst point

When the coffee beans absorb heat and the pressure generated by the evaporation of water inside the beans is greater than the strength of the coffee beans themselves, the cell walls of the coffee beans will burst because they cannot withstand the pressure of the expanding bean core. At this time, the coffee beans will make a popping sound, releasing heat and sound energy. This is the generation of the "first crack". Different flavor compounds are released, and browning occurs. The length of time that the first crack develops determines the changes in the coffee flavor and also determines the key points of the coffee flavor.

Disclaimer: Some of the pictures in this article are from the Internet. For some of the content on the website, such as pictures, we will respect the copyright of the original work and indicate the source, but due to the large number of pictures, some pictures and texts may not be indicated in time, please forgive me. If the original author has any disputes, please contact the website to deal with it. Once verified, we will correct it immediately. It is edited by "Coffee Workshop". Please indicate the source when reprinting. This article is intended to spread coffee culture. If there is any infringement, please inform us to delete it. Thank you~!