The basics of coffee roasting

I. Meaning of baking

1. Definition of baking

The so-called coffee roasting refers to the process of converting raw beans into dark brown raw beans by heating the raw beans to cause a series of physical and chemical reactions inside and outside the coffee beans, and in the process to generate various flavors such as acid, bitterness, and sweetness of coffee, forming alcohol and color.

2. Importance of baking

Among the factors that affect the taste of a cup of coffee, green beans account for 60%, roasting accounts for 30%, and extraction accounts for 10%. Good roasting can bring the personality of green beans to the extreme and minimize the appearance of defective flavors. Conversely, improper roasting will completely destroy good beans. Baking is a difficult technique because of the difficulty in controlling heat, time, and temperature during baking, so the importance of baking is even more prominent.

II. History of baking

As early as the 13th century, Arabs invented coffee beans in a pot, heated and fried, then ground into powder, and then brewed coffee. The early Arabs liked to bake beans lightly, boil them and drink them with spices such as cardamom.

This method of roasting coffee was later spread to Syria, Turkey and Egypt, where it was customary to fry coffee to black, then grind it into powder, add sugar to boil it, pour it directly into a small cup without precipitation, and drink it with coffee grounds.

After coffee was introduced into Europe in the 17th and 18th centuries, Europeans also followed the Turkish style to fry coffee to black.

Later, due to geographical and cultural differences, Europe was divided into light baked pie dominated by northern European countries such as Germany and Britain and Scandinavian countries and deep baked pie dominated by southern Europe. The former usually bakes the beans to city-full-city, while the latter usually bakes them to italy, french, etc.

Accordingly, North America, which was later dominated by immigrants from northern Europe, followed the light baking, while Latin America, which was dominated by immigrants from southern Europe, followed the medium baking.

Until the mid-19th century, beans were roasted at home in iron pans or ovens throughout most of Europe, and small roasting machines were invented that used closed iron drums instead of iron pans and could be controlled by hand to bake a few pounds of beans at the same time, which was adopted by some coffee shops.

With the advent of large baking machines in the mid-19th century, it became possible to bake beans in large quantities. After the advent of large-scale baking machines, they were continuously innovated, and by the first half of the 20th century, electronically controlled precision machines had appeared, and machines that could continuously bake 5000kg per hour could be achieved.

The emergence of large-scale roasters has changed people's habit of baking at home. Buying packaged roasted beans or coffee powder to cook directly at home facilitates the fast-paced life of modern people. By the 1960s, branded packaged beans dominated the market. But there are problems with mass baking: Poor quality green beans, excessive light roasting in order to maintain weight, lack of taste caused by lack of freshness, beginning in the 1980s, a "fine coffee movement" was launched in the United States, which advocated people to buy fine grade green beans, home roasting, drinking fresh coffee, pursuing quality and taste, home roasting began to be valued, and at the same time the pursuit of coffee quality also forced some large roasters to adopt higher quality beans to ensure the quality of roasting.

III. Development and evolution of baking machine

Coffee beans were fried in iron pans in the early days. After coffee was introduced into Europe, Europeans used Turkish iron pans to fry beans on the one hand, and later invented hand-rotating roasting, which could bake several pounds of beans at the same time, which was used by some coffee shops.

In the 1860s, large roasters began to appear, and in 1867 the use of blowers to cool the roasted beans led to the development of large roasters.

At the end of the 19th century, the advent of hot air roasters greatly improved the speed and efficiency of coffee roasting, making it possible to produce larger quantities.

In the 20th century, baking machines combined with electronics were improved to be more sophisticated, fully automated baking machines with more advanced functions.

IV. Current common baking machine types and main brands

(i) Common types of baking machines

1. hot air type

The hot air type bean dryer uses a blower to suck in air, and then let the air pass through a heating coil to raise its temperature. The hot air is used as a heating source to roast coffee beans. The hot air can not only provide the temperature required for roasting, but also use the power of the airflow to stir the coffee beans.

Advantages: high thermal efficiency, fast heating, raw beans heated more evenly, easy to control.

Disadvantages: Because of the high heating efficiency, it is easy to cause the temperature to rise too fast, causing the beans to be "uncooked", and the temperature to rise too high is easy to make the caramelization reaction insufficient.

Taste characteristics: acidity is obvious, taste is relatively clean and simple, but the richness of taste is not enough and lack of depth, and deep baking is easy to produce irritating taste.

2, direct fire

As the name suggests, direct fire is the direct heating of coffee beans with a flame. Evolution so far, the "fire" of direct fire in addition to the general flame (including gas fire and charcoal fire), but also includes infrared rays and electric heating tubes.

Advantages: baking time is longer, so that caramelization reaction is more sufficient, taste is richer,

Disadvantages: It is easy to cause uneven baking, and if the temperature is not well controlled, it is easy to burn coffee beans and form a bitter taste.

3. semi-direct fire semi-hot air type

The baking method combining the advantages of direct fire and hot air is the mainstream of commercial baking machines at present. Semi-direct roasting is actually similar to direct roasting, but because there are no holes on the outer wall of the roasting container, the flame will not directly contact the coffee beans; in addition to this, the exhaust equipment is added to introduce the hot air outside the roasting container into the roasting chamber to improve the roasting efficiency. Another function of this exhaust equipment is to suck out the silver skin that falls off, so as to avoid the silver skin burning in the roasting chamber due to high temperature affecting the taste of the coffee beans.

Semi-direct fire semi-hot air machine has the advantages and disadvantages of direct fire and hot air, but according to the adjustment of hot air and boiler speed to change its heating mode. The larger the hot air is opened, the faster the rotation speed is, the closer it is to the hot air type; otherwise, the closer it is to the direct fire type.

(ii) Major baking machine brands

1. German Probat

Old brands, large and medium-sized machines, semi-automatic, fully automatic all kinds of complete, sophisticated design, expensive.

2. Japanese fuji-royal

Japanese fuji company's products, performance is also good, but also expensive

(3) Introduction to Humen Baking Machine

1kg semi-direct fire semi-hot air roaster, is a coffee machine produced by South Korea Taihuan Company, although there is a certain gap between performance and probat, but compared with its more affordable pricing, this machine is still worth the money, it has power heating and gas heating two kinds, with uniform heating, high thermal efficiency performance, and its appearance design is also very refined.

5. Reactions and changes occurring during baking

1. Drying: When the green beans are heated, the water vapor in the green beans will evaporate, and the green beans will start to turn white at about 135 degrees.

2. dehydration

As the heat proceeds, the green beans turn pale yellow. When the temperature reaches about 160 degrees, they will emit the aroma of baked grain. Continue heating, and the beans will turn light brown.

3. exploded

After about 190 degrees dehydration is completed, due to internal heat expansion caused by cell wall rupture to form a "explosion", then a series of thermal decomposition reactions will occur inside the beans, among which the caramelization reaction will bring the sweetness, dark brown and alcohol of the coffee beans, an explosion will last for about one and a half minutes.

4. secondary explosion

As the heating proceeds, it enters the "second explosion", at which time more intense reactions occur inside the beans. And it gives off a lot of heat. With the end of the second explosion, the raw beans have basically turned black, the beans have expanded to 1.5 times the original, the surface has oil, and the weight has been reduced to about 12%---20%.

5. stop

Usually at the latest after the end of the second explosion about a minute when the temperature reaches 230 degrees when the end of roasting, this time will be a deeper French or Italian roast, when the temperature exceeds 230 degrees and then continue to heat it may make coffee beans spontaneous combustion.

vi. Classification criteria for baking degree

1, roughly divided into light baking, medium baking, deep baking, heavy baking four degrees.

2, each category can be subdivided into two, a total of eight

Light Bake:

Light Light Baked

Medium Cinnamon Baked

Medium baking:

Cinema Medium Roast

High medium deep roast

Deep Baking:

City City Baking

Full-city baking

Heavy baking:

Italy Italian Baking

French French Bake

VII. The technical difficulty of baking and the baker

Because the temperature, heat and other small changes in the baking process can change the taste of beans, different beans have different characteristics, and baking is a quick operation in a short time, so it is required that the baker should master the relevant principles, clearly grasp the characteristics of raw beans, and accurately budget the baking process and adjust it in time during the baking process. In fact, because of the complexity and variability of the baking process, a true baker needs not only theory, but also a lot of experience and perception.