Coffee roasting from a physical point of view

Follow the caf é (Wechat official account vdailycom) and found that Beautiful Cafe opened a small shop of its own.

1. Color deepening

The color of coffee beans changed from yellowish green to light brown, and then gradually to brown, brown and dark brown. This is because the starch in raw coffee beans is converted into sugar, which is further coked. The change of color is the most easily observed phenomenon of coffee roasting, so people describe it the most. Until there was a standard: the baking degree analyzer invented by Agtron Inc in the United States determines the current standard roasting degree of coffee beans by emitting and receiving light on the surface of coffee beans. The deeper the roasting degree, the darker the color of coffee beans, the stronger the light absorption, the weaker the reflected light, and the lower the Agtron value. On the contrary, the lighter the baking degree, the lighter the color of coffee beans, the weaker the light absorption, the stronger the reflected light, and the greater the Agtron value. Baristas can determine the degree of baking through a standard baking color swatch. It is important to note that Agtron baking color value is only one of the auxiliary baking technologies, but can not do more. Two portions of the same coffee beans are roasted to the same Agtron baking color value, but due to the difference in the baking curve, there will be different flavor characteristics and sensory experience. Professional baking needs not only to compare the color, but also to smell the aroma, listen to the explosion, calculate the time, analyze the curve and other methods to be used comprehensively.

two。 Lose water and lose weight

Coffee beans are rich in water, which is divided into free water in free state and bound water locked in cells and adsorbed with organic solids, which is a component of coffee bean cells and a good solvent. In the process of coffee roasting and heating, the weight of coffee beans is reduced by 10% and 15% from free water to combined water. The reason why coffee cooked beans are much more expensive than raw coffee beans, in addition to the substantial increase in the investment in the roasting process, weight loss caused by water loss is also one of the reasons.

3. Volume expansion

With the roasting of coffee, heavy gases such as carbon dioxide begin to spill out in large quantities, and the pressure inside the coffee beans can even reach 20-25 atmospheric pressure, which will cause the coffee beans to expand by 25%, 60%, like popcorn. 4. With the progress of coffee roasting, the original compact fiber structure expands and changes, forming a large number of holes that can be seen under the microscope. Carbon dioxide and volatile aromatic substances escape along these irregular channels, making the original dense and solid coffee beans more brittle-if observed under a magnifying glass. You can see obvious characteristics of sponge, activated carbon or honeycomb structure-oxygen can also invade through these channels, quickly deteriorating the flavor of coffee.