Coffee roasting coffee beans roasting stage explanation

Roasting of coffee beans

Coffee is loved by people, the key lies in the aroma formed after roasting and the taste of drinking, because the coffee bean itself does not have any special taste. "baking" is to change and reorganize the substances inside the raw beans to form a new structure and become people's favorite drink with a strong and mellow flavor.

Coffee roasting is a high-temperature coking (Pyrolysis), which changes the substance inside the raw bean, produces new compounds, and recombines to form aroma and mellow flavor. This effect only happens at high temperatures, and if you only use low temperatures, it will not cause decomposition, no matter how long the coffee beans are roasted.

Most people think that baking is nothing, just stir-fry the raw beans over fire. In fact, in the coffee processing process, baking is the most difficult step, it is a science, but also an art. In the West, experienced bakers enjoy a highly respected status.

Baking can be roughly divided into three stages:

Drying in the early stages of baking, raw beans begin to absorb heat and the internal water gradually evaporates. At this time, the color gradually changed from turquoise to yellow or light brown, the silver film began to fall off, and a faint smell of grass could be smelled. The main function of this stage is to remove moisture, which accounts for about half of the baking time. Because water is a good thermal conductor, it helps to bake the internal substance 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 fast. it is usually best to control the water to reach the boiling point in ten minutes, when the internal material is fully heated and the water begins to evaporate and spill over to the outside of the coffee beans.

When the temperature is decomposed and baked to about 160 degrees Celsius, the water in the beans will evaporate into gas. At this time, the interior of the raw bean changed from endothermic (Endothermic) to exothermic (Exdothermic) and the first burst sound (Crack) appeared. After the bursting sound, it turns to endothermic. At this time, the pressure inside the coffee bean is extremely high, reaching 25 atmospheric pressure. High temperature and pressure began to deconstruct the original tissue to form new compounds, resulting in the taste and taste of coffee; at about 190 degrees Celsius, the transition between endothermic and exothermic took place again. High temperature cracking continued to occur, and the coffee beans changed from brown to dark brown.

After the cooling coffee is roasted, it must be cooled immediately, quickly stop the high temperature cracking, and lock the flavor. Otherwise, the high temperature in the beans will continue to act and will burn off the aromatic substances. There are two ways of cooling: air-cooled and water-cooled. Air cooling is the rapid cooling of coffee beans in three to five minutes with a lot of cold air. 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 air-conditioning. and the pushing arm stirs the coffee beans for cooling. Although the air-cooled type is slow, it is clean and non-polluting, and it can retain the aroma of coffee, so it is used by selected coffee professionals. Water-cooled is to spray a layer of water mist on the surface of coffee beans to make the temperature drop rapidly. As the amount of water sprayed 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.

The roasting degree of coffee beans can be divided into six categories.

Light baking (Light Roasts), cinnamon (Cinnamon), half-city style (Half City), New England style (New England). This kind of baking is only used for absolutely high-quality, fine or highland-grown Arabica coffee beans, mainly for the identification and tasting of coffee beans, generally not on the finished products sold in the market. Cinnamon, so called because its roasted color is very similar to cinnamon, this roasted coffee beans have a lot of acidity, but very little alcohol.

Light to moderate baking (Medium Light Roasts), there are mild American style (Light American), light style (Light City), West Coast style (West Coast). Medium baking (Medium Roasts), including American baking (American), breakfast baking (Breakfast), brown baking (Brown). American roasting is also called "normal" or "brown". When the table is made without oil, the color is darker and is generally used in the roasting of drip coffee. Medium and deep baking (Medium-Dark to Dark Roasts), citywide (Full City), light French (Light French), Viennese (Viennese). Viennese, which means slightly darker than medium baking. This baking has dark brown spots and a little oil on the surface. Deep baking (Dark/High Roasts), including after-dinner style (Afer Dinner), continental style (Continental), European style (European), French style (French), Italian style (Italian), New Orleans style (New Orleans). Continental style can also be called "double roasting", "high", this roasted coffee beans with a similar chocolate color, is described as "very deep", "very important" roasting; Italian, it is mainly used for Italian coffee beans roasting. In the United States, this roasting is darker in color, sometimes called "concentrated" roasting, and the roasted coffee beans are almost black and very oily, and its main flavor comes from the roasted taste rather than coffee. Very deep baking (Very Dark Roasts), there are deep French (Dark French), carbon (Charcoal), in which carbon is rarely used. (the origin of carbonated coffee: Japan is a country that does not produce coffee and accepts coffee relatively late. If the Japanese want to develop their own characteristics of coffee, they roast coffee beans to a very deep degree, similar to carbon, named charcoal.)