The small details that should be paid attention to in roasting coffee beans determine the success or failure of the roasting effect.

Baking this heat treatment causes significant chemical and physical changes in the structure and composition of raw coffee, causing the beans to darken and emit the unique aroma of roasted coffee.

1. The purpose of coffee roasting

The main purposes of coffee roasting are: 1, aroma; 2, increase the complexity of coffee; 3, to obtain color; 4, to form the unique flavor of coffee and so on.

2. The way coffee is roasted

According to the baking time, it can be divided into two types: fast baking and slow baking. According to the baking machine, it is divided into two types: family workshop type and industrial type.

3. The roasting process of coffee

The first stage of baking is heat absorption, in which raw coffee beans are slowly dried until they turn yellowish, when the baking smells like baked toast or popcorn.

The second stage, commonly known as the first explosion, usually occurs around 205℃, during which the coffee beans double in size, change to a light brown color and lose about 5 per cent of their weight.

The third stage is from the first explosion to the second explosion, the temperature rises from 205℃ to 220℃, the color changes from light brown to moderate brown, and the weight loss is about 13%. This chemical process, called pyrolysis, converts the chemical composition of coffee beans and releases carbon dioxide. The third stage is the second endothermic period, followed by the second exothermic period, called the second explosion, the second pyrolysis takes place at about 225230 ℃, baking about medium-deep brown, the sound of the second explosion sounds dense and fast, and the surface of the coffee bean is covered with a layer of oil.

In the process of segmented heating in a bean dryer (usually using a large, hot rotating cylinder), the remaining water in the coffee bean cells turns into steam, prompting the rich carbohydrates, proteins, lipids and minerals to undergo a variety of complex chemical reactions. Coffee beans begin the caramelization process at 170200 ℃. At 185240 ℃, carbohydrates combine with amino acids, peptides and proteins for caramelization, which is known as the "Mena reaction". Caramelization is one of the most important factors affecting the flavor of coffee. After baking for 6-7 minutes, raw beans absorb a lot of heat and start the pyrolysis reaction. Pyrolysis can last until the second explosion, although caramelization is an important process to awaken the aroma of coffee, but with the extension of baking time, some ingredients will also be carbonized to form a bad astringent bitter substance, how to get the highest caramelization. At the same time, carbonization should be reduced to the lowest point, which is the highest technical link of roasting coffee beans. During the roasting process, the volume of coffee beans increases by at least half, while the weight of beans decreases by 1. 5%.

Source: network