Why is coffee so sour? how does coffee get sour?

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The sour ingredients in raw coffee beans are citric acid, malic acid and quinic acid. Phosphoric acid, etc., but this is not the sour taste we feel when we drink coffee. The sour taste we taste mainly comes from the acid produced in the baking process.

When roasting coffee beans, some of the ingredients in the beans will react to form new acids. A more representative example is that chlorogenic acid is decomposed to quinic acid, and sugars are decomposed to form volatile formic acid and acetic acid.

During roasting, raw coffee beans undergo many chemical changes, especially in the middle of roasting (which is lower than the mild roasting on the market), and the sour taste becomes stronger and stronger as the roasting degree deepens. However, after high temperature treatment, the formed acid begins to decompose again, and after this stage, with the deepening of the baking degree, the sour taste becomes lighter and lighter.

Baked beans contain the most acid, which is quinic acid that increases with the deepening of baking. It is not only high in content, but also strong in sour taste, so it is the main source of sour taste of coffee. Other things such as citric acid, malic acid and acetic acid are also high in coffee. The strength and properties of all kinds of acids are different, although they are all sour, but the composition is actually very complex.

The weight and ratio of sour ingredients in roasted beans have a lot to do with the composition of coffee beans. What kind of raw materials are chosen and the way of sour taste release will be different. For example, the carbohydrate content of Carneflora seed which is easy to form acetic acid is low, so it does not form a volatile and irritating sour taste.

In addition, the way of releasing sour taste varies according to the state. There is a substance in quinic acid that can not only emit the sour taste, but also hide it. The reason why the brewed coffee becomes more and more sour is that the sour taste that was originally hidden slowly spreads out over time.