The principle and types of coffee roaster Italian blending of direct-fire, semi-hot and hot-air roaster

1. Direct fire type

The earliest baking tools used by human beings are all direct fire, that is, the drum is heated by fire, and then heat transfer to the raw beans in the cylinder. Although, the motor keeps turning the drum and stirring the coffee beans in the cylinder, in an attempt to make each coffee bean touch the hot iron wall evenly, so as to achieve the goal of balanced baking. However, this baking method still has many disadvantages: the heat conduction speed of iron is not fast, so it must take more time to complete baking; on the outside of the burning drum, the hot gas dissipates in the air, which is a pity that it cannot be well utilized; when the raw bean touches the inner wall of the drum for too long, it is easy to be scorched, resulting in bitterness and scorching taste. When baking, there are a lot of crumbs burst out, left in the tube is easy to adhere to the surface of coffee beans, will make the flavor become chaotic.

2. Semi-hot air direct fire type

Between 1870 and 1920, the German Fan Guban improved and manufactured the barrel roaster. In his baking theory, he refers to coffee beans that bring hot air into roasting. In 1907, the German-made Perfekt roaster began to introduce this concept, using gas heating, there is an air pump, half of the hot gas into the drum, half to the outer barbecue drum. Up to now, roller baking in Germany is still widely used, and the country's Probat drum roaster is famous all over the world.

The general roaster uses gas or electricity as the heat source. In 1987, Derek Company of Idaho took the lead in using the infrared heat source activated by gas, which made the temperature control more accurate and well received, and became the first brand in North America.

Today's drum roasters are almost all semi-hot air direct fire type, on the one hand directly heat the drum with the fire source, on the other hand bring the hot air into the drum. The hot air blown into the drum can increase the heating speed and blow away the debris, thus producing balanced and clean coffee beans.

3. Hot air type

In the 20th century, some people thought of using hot air to bake coffee beans, so that without iron barrier, the heat source can be passed more directly to raw beans and improve baking efficiency. In 1934, the Thermonro roaster (jabez burns thermalo) made by the Bourne Company in the United States, that is, a large type of hot air machine, is still used by some large baking plants in the United States.

4. Air bed roaster

The hot air roaster still adopts the drum design to achieve the purpose of balanced baking by rolling and turning the raw beans. However, some people think of using hot air to move raw beans and let them float up and down, breaking the concept of rollers. In 1976, the American Michael Schweitz designed the air bed roaster. In an airtight container, he let the hot air blow from the bottom up, causing the raw beans to float up and down in the container, and it was not until the baking was finished that he poured out the cooling tray outside the container to cool. In Australia, the well-known coffee expert Iomberstein has a similar design and manufacture.

In the process of baking, the moisture in the beans is evaporated less and less, and the mass becomes lighter and lighter. If you use this kind of roaster, the heavy ones will fall quickly and accept the baking of hot air again, so that even coffee beans can be baked up and down repeatedly. However, the lack of metal drum burning, some people will feel that there is a lack of flavor.