Roasting process, baking degree and roasting curve general knowledge of coffee roasting

The following text is extracted from the book falling in love with barista by Qi Ming, a teacher from Pulan Coffee College, which was printed by Jiangsu Science and Technology Publishing House for the third time in March 2015. Reprint must indicate the author and the source.

One can't make bricks without straw. If the quality of raw coffee beans is not good, no matter how skilled the roaster is, everything is still out of reach. For those coffee beans of poor quality, using shallow roasting is like forcing a bloated person to wear a bikini-the poor body curve is undoubtedly exposed and the weakness is even more prominent. On the other hand, if you increase the degree of baking, you will be able to mask some of the sensory details. Many roasters who advocate shallow roasting put the quality of coffee raw beans in the first place.

First of all, coffee roasters need to accurately grasp the degree of baking. From the appearance, it is the appearance of the color of the bean surface, and from the smell, it is the expression of aroma, but in essence, it is the progress of the chemical reaction in the coffee beans-- in different degrees, the formation of sweet, sour and bitter aroma is different, the flavor presented is naturally different. In the roasting process of coffee beans, a large number of flavor-rich acids are first formed inside. With the continuous improvement of the degree of roasting, the acid in coffee beans gradually decomposed, the sugar converted from starch gradually coked, and the bitterness increased gradually. So we can say that with the improvement of the degree of roasting, the sour taste of coffee beans weakens and the bitter taste increases.

However, it is not enough to know the degree of baking. the process of baking is the process of heat transfer. the complex combination of different forms of heat transfer, such as conduction, convection and radiation, constructs a set of more complex heat transfer efficiency. every second affects the progress of the reaction, and we can only grasp this heat transfer efficiency by observing the temperature rise of the final audience-coffee beans per unit time. Thus controlling the whole baking rhythm, this complete rhythm appears to be the so-called baking curve. We might as well make a summary of coffee flavor: if we stir moderately quickly, the expansion rate of coffee beans increases, the extraction rate increases, the thickness of alcohol increases, the acidity increases, the acidity increases, and the bitterness weakens; if we stir slowly properly, the expansion rate of coffee beans decreases, the extraction rate decreases, and the thickness of alcohol decreases, acidity weakens, bitterness increases.

With the gradual improvement of the degree of baking, the aromatic substances formed are mainly small molecular weight compounds at first (during shallow baking). They are the most active, and a large amount of escape is first perceived by our sense of smell. the odors are mainly floral, grass and fruity, and then when it comes to moderate baking, most of the aromatic substances are medium molecular weight compounds, such as caramel, cream, chocolate, nuts and so on. During the gradual transition to deep baking, the aromatic substances formed are mainly some macromolecular compounds, which are the least active and finally come. In the sense of smell, the smell of resin, spices, charcoal and so on is very obvious.