What we usually talk about most is the brewing of coffee beans. Today Front Street will tell you about the roasting of coffee beans. We know that the process of coffee beans from raw beans to cooked beans is the roasting process, and this process includes light roasting, medium roasting and dark roasting. What kind of coffee beans should be roasted, and how to distinguish between light roast, medium roast and dark roast?
The coffee beans in each producing country have some local flavor characteristics, and to bring out the flavor characteristics of these coffee beans, it requires the skill of the roaster. The Front Street roasters will determine the degree of roasting based on the country, production area, variety, flavor characteristics, etc. of the coffee beans. Of course, when the Front Street roasters get a new bean, they will roast three curves based on the roasting curves of the major production areas for cupping, and choose the curve that is most suitable for the coffee beans.
For every coffee bean roasted by the Front Street roasters, they must record in detail the temperature of the beans entering the pot, the weight of the beans, the temperature recovery point of the beans, the temperature of the boiler per minute, the dehydration point, the first crack point, the first crack time, the release time, the dehydration rate, the temperature rise rate, etc. (the more detailed the better). Various small changes in temperature and heat during the roasting process can change the taste of the beans. Different beans have different characteristics, and roasting is a fast operation in a short time. Therefore, it is required to accurately estimate the roasting process during the roasting process and correct the curve through cupping.
Green coffee beans have an earthy smell before being roasted, but after roasting, they will emit a rich aroma. The roasting degree of coffee beans will also affect the coffee flavor and caffeine content. The lighter the roast, the more sour the fruit and the higher the caffeine content. The darker the roast, the lighter the sourness, the more obvious the sweet and bitter taste, and the lower the caffeine content.
The roasting we are talking about (coffee roasting) refers to the process of heating green beans to cause a series of physical and chemical reactions inside and outside the coffee beans. In the process, coffee's sour, bitter, sweet and other flavors are generated, the body and color are formed, and the green beans are transformed into dark brown beans.
The Front Street roasting coffee bean process is mainly divided into the following stages:
Dehydration period - the coffee beans turn from green to yellow, and you can smell a faint grassy smell
At the beginning of the beans entering, the temperature in the furnace will first drop due to the heat absorbed by the green beans, and then rise again when it reaches the temperature recovery point. The moisture content of green beans is 8% to 14%. As the temperature rises, the free water part will gradually turn into water vapor. The originally hard coffee beans soften, expand in volume, and lose chlorophyll, causing the color to change from green to yellow. The color gradually changes from green to yellow or light brown, the silver skin begins to fall off, and a faint smell of grass can be smelled.
Yellowing stage - the color of the beans is getting darker and darker, and they smell like toast or caramel.
After the coffee beans turn yellow, chemical reactions that form the flavor - Menard reaction and caramelization reaction occur. During the heating process, the sugars and amino acids in the coffee beans will interact to produce complex chemical changes, generating hundreds of aromatic compounds. This process is called the "Menard reaction", which will affect the aroma and taste of the coffee. The beans will also turn light brown due to melanoidins; the "caramelization reaction" is when the sugars are dehydrated into brown caramel before and after the first crack, producing aromatic compounds. The sweetness and bitterness of the coffee come from this, and the color of the beans becomes darker, and the rich aroma of caramel, cocoa, cream, etc. comes from the originally tasteless coffee beans. At this time, the heat should be turned down a little and the damper should be turned up a little to prevent the beans from roasting too fast and causing the beans to be cooked on the outside and raw on the inside.
Flavor development period - hear the crisp and loud popping sound (1 crack), the timing of light and medium roasting of beans
Caramelization and Menard reaction generate a large amount of water vapor and carbon dioxide inside the coffee bean, causing the volume of the coffee bean to expand and increase the pressure. When the cell wall cannot withstand the pressure, it will burst - the center line of the bean will crack, the outer silver skin on the surface of the coffee bean and the inner silver skin in the middle will fall off, making a sound similar to breaking a branch or popcorn. At this time, the coffee beans change from endothermic to exothermic, causing the furnace temperature to rise rapidly. You should reduce the firepower in time and increase the damper to avoid over-roasting the beans. If you want to show the fruity and sour flavor, you should seize the opportunity to release the beans before the first crack is completed.
Flavor development period - the popping sound is dull and small (2 cracks), the timing of adding beans for medium to deep roasting
After the first crack, there will be a resting period of one to two minutes. The coffee beans change from exothermic to endothermic. The interior of the bean continues to expand at high temperature until the cell wall cannot withstand the high temperature and pressure, and a second crack with a smaller sound will occur. The sound of the second crack indicates that the beans have entered the range of deep roasting. Various Italian dark roasts, French dark roasts, and Viennese dark roasts are nothing more than crazy testing on the edge of carbonization. During the second crack, the beans become exothermic again, and due to carbonization and oil rising to the surface, they become even blacker and more shiny.
cool down:Once the beans leave the roaster, they must be cooled immediately to avoid the self-roasting effect causing the beans to be roasted darker than they already have been properly roasted. There are three ways to cool beans:
1) Water cooling: Spray water onto freshly roasted hot beans to cool them down. Since coffee absorbs water easily, this process significantly increases the specific gravity of the bean.
2) Cool with ordinary air.
3) Cool with refrigerated air.
The changes caused by baking are very complex. Although scientists continue to study and analyze them, they still cannot get a full picture. There are roughly the following changes:
Weightlessness: The moisture content drops from about 13% to 1%, and the weight loss is about 12% to 21%. The higher the roasting degree, the greater the weight loss.
Volume expansion:After roasting, the volume of coffee beans will increase by more than 60%. Cell pore enlargement: The cell walls of green beans are hard and the cells are closed, so they are not easy to deteriorate. However, after baking, the cell wall becomes very fragile, the cell pores enlarge, and internal substances are easily lost.
Formation of carbon dioxide: High temperature decomposition causes the carbohydrates inside the coffee beans to decompose and combine with other substances to form a large amount of carbon dioxide, which resides inside the coffee beans.
Change organizational structure: After baking, carbohydrates dropped sharply from 58.9% to 38.3%, and acidic substances (fatty acids, tannic acid, chloric acid, etc.) dropped from 8.0% to 4.9%. Under the action of high temperature cracking, these substances are reorganized and transformed into caramel, carbon dioxide and some volatile substances. Among them, caramel accounts for 25% of the mass of roasted beans, forming the sweet taste of coffee. Fat originally accounts for 16.2% of raw beans, but after roasting it increases to 17%, which is the source of mellow taste and thickness. There was little change in caffeine content. The bitterness of heavily roasted coffee does not come from more caffeine.
Roast degree of coffee beans
Light roast——The color of the beans changes to a delicious cinnamon color, so it is also called cinnamon roast or half-city roast. Acidity dominates the flavor of lightly roasted beans, such as Ethiopian Yirgacheffe coffee.
medium roast―The coffee beans are an elegant brown color. New Yorkers like to start their day with medium-roasted coffee beans, plus fragrant milk and sugar for breakfast. Therefore, this roasting method is also called breakfast roast or city roast. Medium roasting can preserve the original flavor of coffee beans and release the aroma moderately. Therefore, Front Street Blue Mountain Coffee, Front Street Costa Rica Coffee, Front Street Honduras Coffee, Front Street Panama Coffee, etc. all use medium roasting.
dark roast——The darker the color of the coffee beans, the sweeter and more mellow the flavor. At this time, when the oil has turned into caramel, the bitterness is gone and the aftertaste is endless. It is most suitable for brewing strong Espresso coffee, so it is also called Italian roasting method. Such as: Front Street Brazilian beans, Front Street Colombian beans.
Sometimes the coffee beans you see are darker in color, but they are medium roasted or even light roasted. Some are dark roasted and look like medium roasted. In fact, this is because some coffee beans are more pigmented, causing the so-called color difference problem. In response to this problem, the Specialty Coffee Association of America (SCAA) and the American food technology pioneer Agtron developed a set of roasting degree data that is universally applicable in 1996, which is the famous Agtron test. The measurement principle is to use the infrared ray emitted by the analyzer to illuminate the roasted coffee powder, and then reflect it back to summarize the dark and light roasting values.
The darker the roast, the more obvious the caramelization (or carbonization) will be; the darker the bean surface, the weaker the reflected light, and the lower the measured data. On the contrary, the lighter the roasting degree, the lower the carbonization; the less black the surface of the beans, the stronger the reflected light, and the higher the measured value. In other words, the caramelization number (Agtron Number) is inversely proportional to the degree of roast; a higher number indicates a lighter roast, and a lower number indicates a darker roast.
According to Front Street, some baking manufacturers will use Roaster % to indicate the degree of roasting. In fact, this percentage is similar to Agtron. For example, Roaster 95% means light roast, Roaster 90% means cinnamon roast, Roaster 85% means medium roast, Roaster 80% means medium-dark roast, and Roaster 70% means dark roast.
Front Street Brewing Coffee Suggestions:
Front Street does not recommend brewing freshly roasted coffee beans immediately because the carbon dioxide in the coffee beans has not yet been completely discharged and the flavor of the coffee beans is still fully reflected. Therefore, the coffee beans need to be cured. The bean-growing period of coffee is about 4-7 days, and the coffee beans shipped by FrontStreet Coffee are all roasted within 5 days. The purpose of Front Street Roasting is "freshly roasted and good coffee", so that every customer who orders receives the freshest coffee. So the flavor is at its best when customers get it.
For those who need to grind the coffee beans, Front Street would like to remind you that if the coffee beans are ground in advance, there is no need to raise the beans. Because during the transportation process, the pressure generated by the carbon dioxide in the packaging can also make the coffee flavor mellower, so you can make a cup of coffee immediately after receiving the coffee powder. But the coffee powder needs to be brewed in time, because the coffee powder oxidizes quickly when exposed to air, which means that the flavor of the coffee will dissipate relatively quickly, and the flavor of the coffee will not be so good. Therefore, Front Street recommends buying whole beans and grinding them freshly, so that you can better taste the flavor of the coffee.
Professional coffee knowledge exchange. For more coffee bean information, please follow Coffee Workshop (WeChat public account cafe_style)
For more specialty coffee beans, please add FrontStreet Coffee on private WeChat, WeChat ID: qjcoffeex
You can now buy the above coffee beans online at the Taobao store “FrontStreet Coffee” (前街咖啡). FrontStreet Coffee is a long-established specialty coffee roaster in Guangzhou, China, and its Guangzhou retail shop sells coffee beans only. The shop carries dozens of coffee beans from different origins around the world, including carefully selected single-origin beans for V60 pour-over and espresso. Guangzhou’s FrontStreet Coffee shop is recommended by many coffee lovers.
The FrontStreet 2013 Yunnan coffee beans sold in the store come from the Typica variety grown at FrontStreet Coffee’s own plantation in Yunnan. The name comes from the year the brand and the plantation were founded. You can buy these beans from China’s Yunnan origin at the Guangzhou shop and at FrontStreet’s Taobao store.
FrontStreet coffee beans are freshly roasted within 5 days and deliver consistently excellent quality and great value. Orders placed before 17:00 are shipped the same day, and most areas within Guangdong Province receive them the next day.
FrontStreet Coffee Taobao store: https://qianjiecoffee.taobao.com
Or search for “前街咖啡” (FrontStreet Coffee) on Taobao
Important Notice: FrontStreet Coffee has moved to a new address: 315, Donghua East Road, Guangzhou (coffee beans only)
Tel: 020 38364473
