The quality of roasted coffee beans is changeable in flavor and taste. Purpose of coffee baking.

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We all know that the essence of fine coffee lies in each country, each manor, different processing methods will greatly affect the quality of coffee beans, so as to get a variety of flavor and taste. Now there is an acquired flavor in addition to the regional flavor of the raw beans themselves. Regional flavor involves varieties, altitude, planting methods, harvesting and other factors.

Acquired flavor is a small extension of traditional processing methods. For example, there are many "red wine processing methods, whole berry processing methods and" famous "green bean processing methods such as civet coffee. These special treatments "give" some flavor to the beans that were traditionally processed.

However, even the best coffee beans have no taste, just a green bean. One of the mysterious characteristics of coffee beans is that its aromatic compounds are very complex. At present, it is known that there are about 700-850 substances associated with flavor in roasted coffee beans, so it must be roasted if it wants to bloom. Roughly speaking, coffee roasting serves the following purposes:

1. Remove excess water from coffee beans.

2. The wood structure of the coffee beans expands when roasted and has air holes.

3. Start a continuous process of sugar conversion to carbon dioxide gas that doesn't stop immediately after roasting and continues until the beans lose their flavor.

4. Some of the sugar in coffee beans is converted to caramel, and some of the ingredients are converted to fat.

the homogenized

- Transfer heat to the inside and outside of the green beans to prepare all beans for uniform reaction.

Each green bean is made up of countless cells, which include cell walls, cell membranes, cell fluid filling its interior, and cell nuclei. Harvested raw beans will be dried first in order to preserve and circulate, and in the process of drying, part of the water in the cell fluid and cell wall will evaporate, leaving only about 10%--14%. As the moisture content decreases, the size of the cells naturally decreases, and the green beans also become smaller. However, the organic acids and sugars present in the cells remain.

When dried green beans are heated, the heat is transferred to the green beans and changes occur. First of all, the remaining water inside the raw beans will become water vapor when heated, and the volume of water will increase very much (about 1700 times the volume) when it becomes water vapor, so the internal pressure of the heated beans will also increase.

The increase in pressure also causes the boiling point of water to rise, causing water vapor to overheat. Take the pressure cooker as an example. It may be easier to understand the principle of boiling point rise: in the mountains, because the pressure becomes lower, the boiling point also becomes lower, and the rice will be half-cooked. At this time, as long as a stone is placed on the pot, the boiling point will be forced to rise due to the increase in internal pressure. The pressure cooker is designed using this principle. In a pressure cooker with a pressure of 1 bar, the temperature of the water vapor will reach about 125°C, and the same phenomenon will occur inside the cells of the beans.

As the pressure increases, cells that shrink due to drying become larger. Coffee beans are made from coffee cherries, and their cellular tissue is the same as that of trees/plants, so when the volume is enlarged to a certain extent, at some point, the tissue will burst because it cannot withstand the pressure. At this time, the high-pressure water vapor formed inside the cell will be partially discharged, and the other part will be transferred to other cells. Through this process, water vapor at the same temperature and pressure is distributed evenly throughout the cell, almost simultaneously in the whole pile of green beans.

Generally speaking, raw beans will be mixed with large and small beans, each bean has thick and thin parts, which also exist on the dry surface and relatively more moisture internal tissue. If these complex factors are not taken into account, just no matter how hot the beans are heated, the small beans will be the first to burn, and then the large beans will be uncooked, or only the surface will be burned, but the inside will still be partially cooked, so it is necessary to prepare the beans as a whole for uniform reaction.

Inside the beans, moisture moves to prepare the entire tissue for uniform reaction, while outside the beans, heat conduction and convection between the beans rotate together to prepare all beans for uniform reaction. This preparation phase, which allows the beans to react uniformly throughout, is called homogenization.

When homogenized, the beans turn brown and look like dried matter, which we are accustomed to call the "dehydration phase," but the water evaporated during this process is only a small change compared to the first explosion when the tissue itself changes, so the term "dehydration phase" is not correct.

The first crack.

- Tissue swelling and cracking, increased aroma due to baking.

When the homogenization phase is complete, the beans are ready to all react simultaneously. The individual cells are much larger than when the beans were raw, and the tissue thickens as a whole, and if you continue to heat it, the volume will continue to increase, and then just like in the next picture, the center line of the beans will crack. In the green state, the central line is firmly engaged with each other; however, due to the increase in volume, the end parts of the beans on both sides will split, which will make a sound like a branch being broken. At the first explosion, the beans will split like this, and this time they will also start to expel a large amount of water from the inside of the beans.

The process so far is known as the cinnamon-high-city baking phase. The stage at which the first explosion begins is called Cinnamon, the stage at which the first explosion is about to end is called High, and the stage from the end of the first explosion to the end of the second explosion is called City.

telogen

- Active chemical reactions occur inside the beans, which determine the taste of coffee.

The period from the end of the first explosion to the beginning of the second explosion is called the rest period.

As the moisture is expelled, the pressure on the internal tissues of the beans decreases and the tissues temporarily stop growing. Because the beans are in a state where they have expelled a lot of water at this time, if they are reheated at this time, they will not take away heat when they produce water vapor, and the internal heat will rise faster than before.

At this time, the chemical reaction can be more active due to the high temperature, which will generate gas and the tissue will continue to expand. The internal tissue that is cracked at the first explosion will become more expanded and filled. From the outside, the wrinkles on the surface of the beans will gradually disappear, and the beans will become larger.

At this time, the high temperature has been transmitted to each bean, and the chemical reaction inside the beans has reached its climax. The aroma generated by baking is increased, which is an important period for determining the taste of beans. Before the rest period, beans are in the "endothermic period", and at the beginning of the rest period, beans enter the "heating period", but in fact beans do not emit heat, just because compared with the previous stage, the temperature rises rapidly, so it is called for convenience. If the beans react too quickly, they may burn or produce an unwanted bad taste, so fire is usually reduced at this stage.

The Second Crack

- The tissue splits again, creating a strong chemical reaction that enhances the aroma and acidity of the coffee.

After a resting period, when the internal tissues have undergone changes and expanded sufficiently, the cracked internal tissues are filled and the beans continue to grow larger. Then you hear the sound of tissue change again, which is called a second explosion. It will make a sound like a broken matchstick, which is clearer and higher than the first explosion.

At this time, the pressure in the tissue reaches the highest point, and the gas generated inside the beans will begin to be discharged to the outside. The capillary formed in the process of discharging these gases during this period is more related to the extraction of coffee in the future. In other words, only the first burst of coffee beans relatively less capillary formation, so extraction will be less smooth.

From the time of the second explosion, the temperature of the beans will rise more violently, so there will be a stronger chemical reaction inside, making the aroma of coffee stronger. At the same time, the aroma substances produced by baking will also exhibit strong bitterness.

If the second explosion is used as the benchmark, the baking degree before the second explosion is called City, and after the second explosion is Full City. Coffee that continues to roast after the Full City stage is customarily called:

Vienna: The intensive period of the second explosion (also known as espresso baking).

French: The period after the end of the second explosion during which the grease oozes out of the surface.

Italian: The period after the second explosion when the color becomes darker and the oil begins to zoom slowly.

Roasting refers to the process of heating raw beans, which are similar in composition to trees, so if the ignition temperature of wood is exceeded by 250°C, the beans will burn to coke. So heavy baking means before the beans reach 250°C, if the final baked thing is not reddish brown, but completely black, then the beans are turned into charcoal.

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