How much do you know about professional coffee roasting?

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Coffee roasting

Brief introduction of principle

First of all, after baking raw beans at more than 200 degrees Celsius, the moisture begins to evaporate, the volume expands by 60%, and the weight is reduced by 10% to 25. Depending on the degree of baking, the deeper the baking, the greater the weight loss. No wonder many operators do not like re-baking to save costs. Another important phenomenon is exhaust. Raw beans release carbon dioxide during baking and will continue to exhaust for 30 days after baking. Interestingly, carbon dioxide emissions contribute to the preservation of coffee beans, because during the exhaust process, oxygen molecules are not easy to invade, that is, the oxidation that destroys the flavor of coffee cannot be carried out, but the exhaust gradually slows down after seven days of baking. Oxygen molecules are easily attached to the bean surface, and the flavor of coffee decays quickly, which is an important reason why coffee beans are best used within a week after opening.

Achieve the highest caramel and least carbonization. Caramelization is a link that has the greatest impact on the flavor of coffee. After six to seven minutes of baking, raw beans absorb a lot of heat and start the pyrolysis reaction, resulting in the first explosive sound. Some sugars are converted into carbon dioxide, and water continues to evaporate. New aromatic components gradually develop into the so-called coffee oil. And combine with hundreds of aromatic substances such as nicotinic acid, citric acid, quinic acid, malic acid, acetic acid, caffeine and so on. Pyrolysis reaction can continue to the second explosion, although caramelization is an important process to awaken aromatic elves, but with the extension of baking time, some ingredients will also be carbonized to form a bad astringent bitter substance, how to obtain the highest caramelization, but also to minimize carbonization, which seems to be contradictory, but it is the biggest challenge for bakers.

Pay attention to the changes of sound, color and taste. The chemical reactions mentioned above can be judged by listening to the sound, seeing the color and smelling the smell. The color of coffee beans will change from gray to golden brown to light brown, then to reddish brown with a trace of oil, and then a large amount of oil to dark brown. If it continues to bake, the coffee oil on the bean surface will become dry, dead black, and emit a lot of blue smoke with a scorching smell. This is a warning that is close to ignition. Prepare to call 119 to help put out the fire. Experienced bakers will choose between light brown to oily dark brown for safety. Coffee beans change from shallow to deep because of changes in caramelization and acidity.

Listening to sound is also the basis for judging the degree of baking. If the temperature of the roaster is hot enough, coffee beans will burst twice during the roasting process. For example, high-temperature-resistant raw beans such as Mantenin and Angelica will burst for the first time in about seven minutes, and the sound will be low and sparse. This means that the "pyrolysis" is started, that is, the starch begins to be converted into caramel, and water is ejected from the bean surface with carbon dioxide, making a low burst sound, which is quiet for two minutes. At about 12 minutes, there was a more violent and sharp burst, which was the sound of broken fibers in coffee beans, which indicated that the baking was coming to an end, and the fragrance would fade if it went on. We can see that coffee beans can talk.

To sum up, coffee roasting is a science, and the age, density, hardness and moisture content of raw beans will affect the quality of roasted coffee. Even the relative humidity and temperature on the day of baking can not ignore the coffee beans that have just been baked. It is best to put the coffee beans for 2-5 days, so that it will be easier to drink after a large amount of carbon dioxide is discharged. Hong Kong coffee will choose an one-way breathable valve aluminum foil bag to preserve coffee beans, which can prevent air entry and cause oxidation, but also allow carbon dioxide emissions to ensure that coffee beans are kept in the best condition of freshness.

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I don't know if it's clear.

The above explains the simple process of roasting coffee.

Of course, there are still a lot of knowledge about coffee roasting waiting to be learned, such as the selection of coffee beans, roasting skills, some precautions and so on. With regard to all the above, we will follow up and hope that you can continue to pay attention.