Where does the sour coffee come from? Why does the coffee become more sour when it is cold? With coffee.

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Front Street Coffee brief description where does the acid in the coffee come from?

The sour ingredients in raw coffee beans are citric acid, malic acid, quinic acid, phosphoric acid and so on, 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 undergo chemical changes to form new acids. For example, chlorogenic acid decomposes after heating to form quinic acid, and sugars decompose to form volatile formic acid and acetic acid.

Quinic acid is also a kind of phenolic acid, accounting for only 0.3%-0.5% of the weight of raw beans, but when coffee is roasted, chlorogenic acid is continuously degraded into quinic acid to increase its concentration gradually, and finally quinic acid accounts for about 0.6%-1.2% of the weight of ripe beans, that is, the concentration of quinic acid after baking is more than twice that before baking. After entering the second explosion, the concentration of quinic acid reaches the maximum value of 3, and continues to bake after entering the second explosion, quinic acid will rapidly degrade from the peak to the aromatic components phenol (also known as carbolic acid), catechol, hydroquinone and pyrophenol, which makes the flavor of deep baking different from that of shallow baking. It can be seen that quinic acid is quite stable during baking and will not decompose easily unless it enters an unusual re-baking.

In addition, when the coffee is soaked and cooled, the sour taste will be enhanced, which is also related to quinic acid, because the unsour quinine lactone will be hydrolyzed into quinic acid and increase the sour taste.

Is quinic acid dead acid or lively aromatic acid? There are two theories. R.J.Clarke, author of The Flavour of Coffee, believes that too much quinic acid can cause the bitter taste of deep-baked beans, and quinic acid is also the culprit for the sour taste of coffee in thermos after brewing and staying in thermos for a long time. However, the research report of the American Fine Coffee Association (SCAA) takes a positive view, believing that quinic acid is water-soluble and will all be dissolved into the cup, which will not only increase the thickness of alcohol, but also increase the complexity and clarity of coffee.

In addition, caffeic acid, another product of chlorogenic acid degradation, also belongs to the phenolic acid family, slightly astringent and antioxidant.