The roasting process of coffee is explained in detail. How does the roasting stage affect the flavor of coffee?

Roasting is one of the most attractive parts of the coffee industry. Raw coffee beans are almost tasteless and have an unpleasant vegetable taste, but roasted raw beans are transformed into incredibly fragrant, complex and varied ripe beans. That is, we usually come into contact with, whether it is the purchase of coffee bean bags, or in the coffee shop to taste delicious coffee, are roasted delicious.

Baking stage and Flavor effect

In short, the roasting of coffee actually refers to how deep the final color of the coffee bean is (light roasting to deep roasting) and how long it takes (fast or slow). Different roasting speed will affect the performance of different flavors. When roasting coffee, many reactions will reduce weight and lose moisture. Slow frying (finished in 14-20 minutes) will have a high weight loss ratio (about 16-18%), while quick-frying can be completed in 90 seconds. For an expensive cup of high-quality coffee, slow stir-frying will lead to better flavor development.

In the roasting process, there are three important factors that determine the final flavor of coffee: sour, bitter and sweet. In general, the longer the total baking time, the less acidity is left. On the contrary, the bitterness increases with the baking time. The development of sweetness is curved, between the peak of sour and bitter taste, and a good baker knows how to make a coffee bean reach the highest sweetness in every degree of roasting. But whether you use a baking method that makes it sour and sweet, it may not help if you use shoddy coffee beans, even though the roasting method is adjusted to more advanced levels.

The first stage: removing moisture.

Coffee beans contain 711% moisture, which is evenly distributed in the tight structure of the whole coffee bean. when there is more water, the coffee beans will not turn brown. after pouring the raw coffee beans into the bean dryer, it takes some time for the coffee beans to absorb enough heat to evaporate the excess moisture, so this stage requires a lot of heat.

The second stage: turning yellow

After the excess water is brought out of the coffee beans, the first stage of browning begins. At this stage, the structure of the coffee beans is still very tight and has a similar aroma like Indian rice and toast. Soon, the coffee beans will expand, the silver skin on the surface begins to fall off, and the exhaust device of the bean dryer is discharged into the silver skin collection bucket. The first two stages are very important. If the moisture of the raw coffee beans is not properly removed, the subsequent baking stage will not be able to achieve uniform baking, even if the coffee beans look fine on the outside, but they may not be ripe on the inside. the flavor after brewing is very unpleasant, leaving the bitter taste on the surface of the coffee beans and the undeveloped sharp sour and grass taste of the bean core. After this stage, it is difficult to save even if you slow down the baking speed, because different parts of the same bean will develop at different rates.

The third stage: the first explosion

When browning starts to accelerate, large amounts of gas (mostly carbon dioxide) and water vapor begin to be produced in the coffee beans. when the internal pressure increases too much, the coffee beans begin to burst, make a crisp sound, and expand nearly twice as much. It was then that the flavor of coffee beans as we know it developed, and the baker could decide when to end the roasting of coffee beans.

The fourth stage: flavor development stage

After the first explosion, the surface of the coffee beans will look smoother, but there will still be a few wrinkles, which determines the final color depth of the coffee and the actual depth of roasting. The baker must grasp the sour, bitter and sweet taste of the final cooked bean product. The longer the baking time, the higher the bitter taste.

Stage 5: the second explosion

At this stage, the coffee beans burst again, but the sound is subtle and dense. Once the coffee beans are roasted to the second explosion, the internal oil is easily brought to the bean surface, and most of the sour taste will fade and produce another new flavor, which is often called "baking flavor". This flavor does not vary according to the type of beans, because it is caused by carbonization or coking rather than internal flavor components. However, it is dangerous to bake coffee beans in the second explosion stage.

Sugars and acids in coffee beans

Coffee beans contain a certain degree of monosaccharides, although not all sugars are sweet, but these monosaccharides are usually sweet and can easily react under the catalysis of coffee baking temperature. once most of the water in the coffee bean evaporates, the sugar will begin to react differently with the heat, some of which will play a caramelization effect, causing some coffee beans to have caramel-like tonality, especially The sweetness of these caramelized sugars will decrease and may eventually become one of the sources of bitterness.

There are many kinds of sour taste in the coffee beans, some of which taste pleasing and some of which are not delicious. For bean bakers, one of the most important acids is chlorogenic acid. when baking coffee, one of the key goals is to completely remove untasty acids while avoiding creating more negative flavor factors and retaining the most delicious aromaticity.