The three elements that affect coffee are generally divided into pot, bean, and roast. The percolator refers to the machine used to roast coffee. Roasting stability and controllability are related to flavor reproducibility. That is to say, occasional tasty roasting is not something to appreciate; good taste must reproduce again, maintaining a certain level. Therefore, machine manufacturers have put a lot of effort into this aspect. In addition to the increasingly accurate temperature measurement, thanks to the advancement of technology, the new cereal roasters of recent years can even adjust the damper according to the data established by the computer and the firepower, trying to minimize the error caused by human operation.
When roasting is stable and controllable, the result can be predicted from the quality of the raw beans. What is put into the machine will come out. The moisture content and texture of the green beans will be affected during the roasting process. Fresh green beans have a rich aroma and flavor after roasting at a high temperature. If they are stored for too long or in the wrong storage environment, the flavor of the green beans will be lost, and the result will be unsatisfactory.
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Roasting skills are placed last because the difference between the same type of green beans when using the same machine and adopting the correct roasting method is an expression of what is known as a personal roasting style. The biggest difference is usually due to the depth of the roast, which makes the coffee's acidity, sweetness, bitterness, and thickness differ. Preserved flavor and cleanliness is also key point.
Understand the design principle of the coffee roasting machine.
Take, for example, the bean roasting machine made in Taiwan. During the roasting process, the functions that can be controlled include the power of the gas fire, the discharge valve, and the speed of the boiler; temperature observation values provided include grain temperature in the kiln and air outlet temperature. There are viewing windows and sampling sticks to judge the look and smell of the green beans.
The continuously rotating kettle allows you to heat the green beans evenly. The good design of the baffle of the kettle makes it more lively and nervous when stirring and prevents burns. When the rotation speed is slow, the green beans will stay in contact with the kettle for a long time; when the rotation speed is fast, the green beans will be thrown into the hot air for a long time, affecting the taste. However, baking machines from Germany, Japan, and the United States cannot adjust the kettle speed.
In addition to firepower, the distance between the gas fire row and the boiler called the fire distance, is also a big problem in the design of the machine. The most common modification to Japanese brand bean roasters is to increase the number of gas nozzles and extend the shooting distance. The question of uniform heating is also considered. The new machine made in Taiwan has changed the gas nozzle to a three-row double switch design, which can be switched according to the amount of cooking to increase the flexibility of operation.
Turn on and heat; the heat energy will heat the coffee beans through three types of conduction, convection, and radiation.
Utility. In addition to the full hot air type, which primarily uses convection heat, we often hear of two machines: semi-hot air and direct fire. Simply put, the wall of the direct-fire roaster's roasting chamber is perforated, allowing radiant heat to act directly on the green beans. Such a machine can also have a far infrared kit to maximize radiant heat.
The semi-hot air machine mainly uses conduction heat and convection heat. When firepower is fixed, controlling exhaust valve size is the main factor affecting convection heat.
We must first understand that green beans are the hard seeds in the coffee bean. In addition to crude fiber, they contain water, chlorogenic acid, protein, alkaloids, caffeine, fat, sugar, and other substances. During high-temperature roasting, the above substances will undergo chemical changes such as Ore reaction and Stryker degradation, thus producing coffee tannins, tobacco acids, aromatic esters, alcohols, carbohydrates, and other substances affect the taste of coffee.
So, regarding the problem of roasting coffee beans, we can understand it as a process of increasing the temperature, but it must take place under controlled conditions. For this reason, the temperature and the heating rate during cooking are the main reasons for the difference in taste.
In the roasting process, we can observe the color change of the green beans, from greenish-green when the moisture content is high to a white-yellow after high-temperature roasting to remove most moisture. As the temperature rises, it gradually turns yellow. When it reaches the temperature where the reaction of the mineral occurs, the surface obviously turns brown and gradually gets deeper. If the heating is continued, charring will occur, and the coffee beans will become dark black with a shiny, greasy surface. If the heating is not stopped, it will eventually catch fire.
In addition to the color change, the volume of the coffee beans will also undergo various variations. In addition to a small degree of thermal expansion, there will be two explosions at different temperatures, and the volume will increase by up to 60%. As the volume expands due to the loss of water and the removal of the silver skin, the total weight will also decrease, with a weight reduction of approximately 12-20% when firing from light to dark.
In addition to the roasting temperature and time, we can preliminarily judge the roasting degree of coffee beans by the appearance color, volume change, and weight loss ratio. It can also be detected via the Agtron Caramel Spectrum Analyzer for accurate roast depth.
The coffee roaster will face several difficulties. Only by knowing the principles of coffee roasting, accumulating experience, and adapting to changing circumstances can a barista master excellent skills.
YBaking is a science. Ou doesn't have to ignore all the production links to do a good baking job. The selection of materials must be careful, the weighing of materials must be accurate, and the operation must be careful. To understand the principle of cooking, you must first understand the three methods of heat conduction, convection, and radiation.
Conduction refers to the conduction of heat from a heat source, causing surrounding molecules to vibrate and release heat energy, gradually moving from a place of high temperature to a place of low temperature. Conductive stainless steel has uneven heating, making some parts of the pan colder and hotter.
Convection means that when a substance is heated, the fluid substance or gas rises due to volume expansion and density reduction due to heating, and its position is replenished by the exchange of surrounding cooler and denser fluids, so it is heated and the surrounding substances are replenished. This continuous heating motion is called convection.
Radiation requires no medium; heat can be radiated directly to the object to warm it. The most used radiation methods for food are dielectric, microwave, or infrared. In the specific cooking operation, two or three cooking methods are used simultaneously depending on the environmental conditions of the time.
The problems that are often encountered in the coffee roaster stage are as follows:
1. The preheating temperature of the roasting chamber is insufficient, and the coffee beans are immediately placed in the oven, thus extending the roasting time. Therefore, the roast loss is high, and the color of the coffee beans is light. This is because the heat is insufficient, and the leather cannot be completely charred, resulting in a lack of color and rough inner fabric.
2. The oven temperature in the cooking space is too high. When the coffee is roasted, a crust forms prematurely on the surface, suppressing the internal tissue's expansion. Since the surface is colored rapidly, the operator mistakenly thinks the product has been roasted and ends the roasting prematurely. The inside of this type of bean is sticky and thick, doesn't have the proper expansion, and doesn't have the normal flavor.
3. Idling is too long after warm-up. The internal oven that has been empty for too long accumulates too much heat. The temperature in the oven causes uneven heating of the coffee beans inside and out. After the coffee beans are placed in the oven, all heat sources will concentrate on the surface of the beans in the initial stage of the roasting process, forming a fire that is too strong, and then the heat disappears, and it cools down quickly. , which is unstable.
4. The cooking time is too long or too short. The height of the roasting temperature and the duration of the time must be adjusted with the number of beans. A small number of cooking chambers have more space, and metal conducts heat and radiates more heat energy, so the temperature must be lower; and when the number is larger, the temperature can be higher. The duration of the cooking time should also be flexibly adjusted. Generally, when beans are heated in the oven, heat energy is absorbed by the surface and surroundings and transferred to the center of the beans. Thus, the roasting condition of the beans can be observed by changes in the appearance of the beans.
5. I have not developed a good habit of registering and cooking by touch, resulting in insufficient stability and unable to form my database of cooking curves sufficient as a reference for future cooking.
From the previous up-and-down method of direct or gas fire to the type of electric heating commonly used today, the design of power convection has been continuously improved. Also, the difference in toaster type and performance will cause a difference in cooking time and temperature. At the same time, installing a fan improves the stability of heat convection, makes the color of roasted beans more uniform, and saves electricity and cooking time.
Advanced tools and equipment simplify the cooking process, and it is equally important for the operator to accumulate cooking experience.
In short, coffee roasting will have to face several difficulties. Only by knowing the principles of coffee roasting, accumulating experience, and adapting to changing circumstances can baristas master excellent skills.
Roasting of coffee
The aroma of the coffee and the character enclosed in each bean are released through the fire's combustion: acidity, sweetness, and bitterness are vividly released, from the smooth raw beans to the soft aftertaste in the cup. Cooking is key to any bean. The long journey of a coffee bean is the most important step in defining the character and developing the aroma.
Whether in a professional roastery, over your fire, or in an oven, the coffee beans undergo many chemical reactions during this 12-16 minute process at a temperature of up to 240 degrees Celsius. Switch it up, pop a crisp sound like a second popcorn, and lose 10% - 20% of your water by weight.
IGreen Beans - Each coffee cherry contains two green beans. t is filled with aroma and a pleasant bouncing sound like popcorn during the cooking process. From the green beans, light roast, medium roast to dark roast, the moisture is released repeatedly, and the weight decreases. Still, the volume slowly expands, the color of the coffee beans deepens, the fragrance oil is gradually released, and the texture becomes crunchy. The scent is still deep inside her, waiting to be discovered. Green beans contain many chloric acids, which gradually disappear during roasting, releasing familiar and pleasant fruit acids such as acetic acid, citric acid, and malic acid into the wine. A good roast can bring out this wonderful acidity in moderation. Conversely, an excessive roast will cover it completely. When roasted for 5-7 minutes, the beans begin to release water, turn from light green to orange, and give off a unique aroma like creamy roasted vegetables.
Light roast: When the beans make the first light sound, the volume expands simultaneously, and the color changes to a delicious cinnamon color, which is also called CINNAMON RAOST or HALF-CITY ROAST. The acidity dominates the flavor of the lightly roasted beans, and the texture and flavor have not yet been fully developed. Therefore, they are usually used as canned coffee and may not satisfy true coffee connoisseurs.
Medium-roasted, the coffee beans have an elegant brown color. The character of the coffee beans is also clearly defined. New Yorkers like to start their day with medium roast coffee beans, rich milk, and sugar for breakfast, which is why this roasting method is also called BREAKFAST ROAST or CITY ROAST. The medium roast can preserve the original flavor of the coffee beans and release the aroma moderately. Therefore, single-origin coffees such as Blue Mountain, Columbia, Brazil, etc., often choose this roasting method. When the roast is deeper, the fat rises to the surface, and the kernels are burned with the fire model to burn a glossy dark brown color called FULL CITY ROAST. Some people think that at this moment, coffee's tart, sweet and bitter taste reaches the perfect balance point.
Deep Roast – The darker the color of the coffee beans, the sweeter and smoother the flavor. At this moment, when the fat has turned into caramel, the bitterness will be sweet, and the aftertaste will be endless. It is best suited for making strong ESPRESSO coffees, also called the Italian roasting method. Moderate roasting brings the coffee beans to life, transforming them into the intriguing tart, sweet, bitter, and astringent flavors. However, those sensitive to caffeine may choose dark roasted beans as much as possible because the caffeine escapes slowly during roasting. The darker the roasted beans, the lower the caffeine content.
Please note: The bitterness and acidity of the roast will continue to vary with different coffees, and the primary method of consumption varies from person to person.
Publication Date: 4/19/2023
Category: Product Events
