Coffee roasting knowledge II

III. The concept and principles of coffee roasting

As the name suggests, roasting is to provide heat to coffee beans, causing a series of chemical changes inside. Raw coffee beans show the unique color, aroma and taste of coffee by roasting. Every coffee bean contains fragrance, sour taste, sweet taste and bitter taste. How to release it incisively and vividly depends on the heat of baking.

From the insipid raw beans to the mellow aftertaste in the cup, baking is a very important step in the long journey of every coffee bean to outline its character and nurture its fragrance. Coffee beans are about 20 minutes long (inversely proportional to the temperature) and the temperature is as high as more than 200 degrees Celsius. In the process of dialogue with hot cuts, coffee beans have undergone many chemical changes. First of all, the starch in raw beans will be converted into sugars and acids because of high temperature, while substances such as cellulose will be carbonized to varying degrees. Water and carbon dioxide evaporate, while proteins are converted into enzymes, which combine with the rest of the fat to form an oil film on the surface of coffee beans. Coffee beans swell after roasting, giving off a primary explosion, a secondary explosion, a sound like popcorn, and loss of moisture. But because the skin on the surface of coffee beans is very tough, we usually don't see coffee beans crack like popcorn. From raw beans, light roasting, medium roasting to deep roasting, the water is released again and again, the weight is reduced, but the volume slowly expands, the color of the coffee beans deepens, the fragrant oil is gradually released, and the texture becomes crisp.

In raw beans, there is a lot of chloric acid, which gradually disappears with the baking process, releasing familiar and pleasant fruit acids, such as acetic acid, citric acid and malic acid in wine. Baking moderately presents these sour flavors.

We often see that roasted coffee beans have different shades of color. On the one hand, this may be due to different types of individual coffee beans; on the other hand, the main reason for this color difference is the degree of roasting. In the most popular language, the degree of baking can be interpreted as the heat of baking. Take the most classic example of carbonated coffee, a French roasted coffee that is highly carbonized, dark brown and carbon black due to its deep roasting (either because of the high temperature during baking, or because of the long baking time, or both, depending on the situation). It is generally believed that carbonized coffee tastes bitter, which comes not only from caffeine but also from carbonized coffee beans.

The principle of baking: the most important thing in baking is to be able to stir-fry the inside and outside of the beans evenly. First of all, the moisture in the beans will be discharged smoothly through firepower. If this step is too hasty, it will be spotted, and the taste will be astringent and choking.

80% of the taste of coffee depends on roasting, so roasting is an important process for brewing good coffee. If the baking technology is good, the beans will be large and swollen, with no wrinkles and luster. Roasting coffee beans into their ultimate characteristics is the ultimate goal of baking.

The flavor of coffee not only depends on the variety of coffee, roasting is also a decisive factor.

Basically, the roasting of coffee is a kind of high-temperature coking, which completely changes the substances inside the raw beans, produces new compounds, and recombines to form aroma and mellow flavor. This effect will only occur at high temperature. If only low temperature is used, it will not cause decomposition, and no matter how long it is roasted, coffee beans will not be cooked.

IV. The process and stage characteristics of coffee roasting

Baking process

Most people think that baking is nothing, just frying the raw beans with fire. In fact, in the process of coffee processing, roasting is the most difficult step, it is a kind of science, but also an art, so in Europe and the United States, experienced roasters enjoy a highly respected status. Baking can be divided into the following three stages

1. Drying

In the early stage of baking, the raw beans begin to absorb heat, and the water inside gradually evaporates. At this time, the color gradually changed from green to yellow or light brown, and the silver film began to fall off, you can smell a faint smell of grass. The main function of this stage is to remove moisture, which accounts for about half of the baking time, because water is a good heat transfer conductor and helps to bake the internal material of coffee beans. Therefore, although the aim is to remove water, the baker will make good use of the temperature of the water and properly control it so that it will not evaporate too quickly; in general, it is best to control the water to reach the boiling point and turn into steam in 10 minutes. At this time, the internal material is fully cooked, and the water begins to evaporate, rushing out of the outside of the coffee beans.

2. High temperature decomposition

Baked to about 160 degrees Celsius, the water inside the beans will evaporate into gas and begin to rush out of the outside of the coffee beans. At this time, the interior of the raw bean changed from endothermic to exothermic, resulting in the first burst sound. After the bursting sound, it turns to endothermic again, and the pressure inside the coffee bean is extremely high, up to 25 atmospheric pressure. Heat and pressure begin to deconstruct the original tissue to form new compounds that create the taste and taste of coffee; at about 190 degrees Celsius, the transition between endothermic and exothermic occurs again. Of course, high temperature cracking continues to occur, coffee beans from brown to dark brown, gradually entering the stage of re-baking.

3. Cooling

Coffee must be cooled immediately after roasting, quickly stop the pyrolysis at high temperature and lock the flavor. Otherwise, if the high temperature in the beans continues to work, the aromatic substances will be burned. There are two cooling methods: one is air-cooled and the other is water-cooled. The air-cooled type requires a lot of cold air to cool the coffee beans quickly within 3-5 minutes. In the field of professional baking, large roasters are equipped with a tray with a rotatable driving arm; when the baking is completed, the beans are automatically fed into the tray, and the fan at the bottom of the tray is immediately activated to blow cold air. And the pushing arm stirs the coffee beans to cool them. Although the speed of the water-cooled type is slow, it is clean and does not pollute, and it can better retain the aroma of the coffee, so it is used by the selected coffee industry. The water-cooled method is to spray a layer of water mist on the surface of the coffee beans, allowing the temperature to drop rapidly. As the amount of spraying water is very important, it requires precise calculation and control, and will increase the weight of baked beans, which is generally used in large-scale commercial baking.

Baking degree and characteristics

From the point of view of the baking degree, the deeper the baking degree, the stronger the bitter taste; the lighter the baking degree, the stronger the sour taste. The choice of baking degree depends on the characteristics of the coffee bean itself. for coffee beans with strong bitterness and light sour taste, they generally choose a moderate and shallow roasting degree.

1. Shallow baking (Light)

The most mild fried culture, no fragrance and concentration to speak of, the beans are not yet ripe, with the green taste of raw beans, not suitable for grinding and drinking. It's usually used as an experiment.

2. Deep shallow baking (Cinnamon)

Also known as cinnamon baking, for the general popular degree of frying, leaving a strong sour taste. The color of beans is quite similar to that of cinnamon, so it is also called cinnamon baking and its sour taste is aggravated. It is favored by people in the western United States.

3. Shallow medium baking (Media)

The color deepens, easy to extract the original taste of coffee beans, mellow, sour and delicious. Mainly used for mixing coffee.

4. Medium baking (High)

Coffee has a stronger flavor and a lighter sour taste, which is the general roasting method of coffee beans. The sour taste is neutralized and bitter, suitable for coffee such as Blue Mountain and Kilimanjaro. It is loved by Japanese and Nordic people.

5. Deep medium baking (City)

Also known as city baking, bitter taste is stronger than sour taste, almost no sour taste, unique flavor. Coffee suitable for Colombia and Brazil is very popular in New York.

6. Normal baking (Full City)

Also known as city-wide baking, suitable for brewing iced coffee. No sour taste, mainly bitter taste, bitterness will be aggravated, but high-quality beans will have sweet taste. It is used for iced coffee and is preferred by people in Central and South America.

7. French baking (French)

French baking method, slightly black color, strong bitterness, but also ooze oil, bitterness and concentration are deepened. Coffee used for steam pressurizer.

8. Deep baking (Italian)

Also known as Italian baking, the deepest baking degree, the beans are black and bright, the surface is oozing oil, the bitterness is very strong. At this stage, coffee beans have been seriously carbonized, and it is difficult to distinguish the taste of one kind of coffee bean from another. For Italian steam pressurized coffee.

Baking characteristics all over the world

Cities all over the world have their preference for frying and baking.

In Tokyo, micro-deep medium baking is more popular, but slowly it also tends to deep baking. In the West, deep baking has been popular since ancient times.

New York, as its name suggests, generally prefers urban baking, but because it is inhabited by different races of people, it sells coffee beans of different roasting levels, which are quite varied.

Vienna prefers deep baking. The French prefer French baking, while Italians often use Italian baking.

However, in recent years, Italian baking (the most commonly used deep roasting in Brazil and Italy) has been widely used in Europe and the United States, and the coffee made by steam pressurizer is still popular.

Deep roasting of Ethiopian coffee beans would be a waste. Because that would lose the unique characteristics of this coffee. Black roasting of Yauco and Kona coffee beans is also bad, because you will lose the classical flavor you pursue when you buy it.

When some coffee beans are roasted black, new and interesting qualities will be derived. Mexican coffee beans produce an interesting sweetness when roasted in black.

Guatemala Antigua coffee beans seem to retain their sour and fruity flavor when they are deeply roasted, which is difficult for other coffees.

Sumatran coffee beans are usually full-grained, but are below medium acidity, lose acidity when roasted deeper, and easily turn into sugar paste.

Generally speaking, the darker the baking, the lower the quality. Deeper roasting means losing most of the flavor of the coffee beans.

Roast coffee beans at home

The hardest part of coffee-related activities is baking coffee beans at home. When making high-quality coffee, whether the beans are fresh or not is very important.

The easiest way is to bake coffee beans in the oven. The biggest advantage of this is that it adjusts the temperature so that the smell of roasted coffee does not pervade your home. Heat the oven to 230 degrees in advance. Remember to keep the coffee beans well ventilated and don't spread the beans too thick. After baking for about 10 minutes, observe the change of color. Pay attention to the crackling sound of coffee beans and check the color all the time. When the coffee beans are only a little lighter than you want, remove them from the oven to cool. The residual heat will cause the coffee beans to continue to be heated for 2 Mel for 4 minutes.

Home baking stoves can also be used, but the best is the traditional flat-bottomed pan or popcorn (popcorn) model. Use a handle to manipulate two vertical pieces of metal inside the machine, which can rotate the coffee beans during baking. This can be bought in a second-hand store or a good kitchen utensils store, where you can also buy inexpensive oven thermometers.

After the coffee is roasted, take them out of the grill, put them in a heat-resistant bowl, and put the bowl by the window or outdoors.

The operation of crushing roasted coffee beans into powder is called grinding. The props used to grind coffee beans are called grinders.

The ideal time to grind coffee is before cooking. Because the ground coffee is easy to oxidize and lose its flavor, especially when it is not properly stored, the coffee powder is easy to change flavor, and it is naturally impossible to cook mellow coffee.

Some people are afraid of trouble or don't want to buy more bean grinders. They usually buy ready-made coffee powder when drinking coffee at home. At this time, they should pay special attention to storage. If the climate is humid, it is best not to place coffee powder at room temperature after opening. A more appropriate way is to put it in a sealed jar and refrigerate it, and do not place it with garlic, fish and shrimp and other heavy-flavored food. Because the coffee powder is easy to absorb, a careless coffee becomes a strange taste coffee, then even the best quality coffee will be spoiled. However, some people put the cooked coffee powder in the refrigerator as a deodorant, which is a good way to make the best use of things.

When grinding beans, the size of the powder depends on the way it is cooked. Generally speaking, the shorter the cooking time, the finer the ground powder; the longer the cooking time, the thicker the ground powder. In terms of actual cooking, the ESPRESSO machine takes a very short time to make coffee, so the grinding is the finest, and the coffee powder is as fine as flour; it takes more than a minute to cook coffee by plugging the air, and the coffee powder is medium-sized grinding; American filter coffee takes a long time to make, so the coffee powder is the thickest.

Grinding coffee powder with the right thickness is very important for making a good cup of coffee, because the extraction of water-soluble substances in coffee powder has its ideal time, if the powder is very fine and cooked for a long time, resulting in excessive extraction, the coffee may be very bitter and lose its aroma. On the other hand, if the powder is coarse and cooked too fast, resulting in insufficient extraction, the coffee will be tasteless because it is too late to dissolve the water-soluble substance in the powder.