Why does the coffee turn sour when it's cold?

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Many friends will prepare a cup of coffee for themselves at work and study, but when they get busy or procrastinate, they will forget to finish the coffee while it is still hot. When you pick up the cup again, you will find that the coffee has turned sour! Is this the punishment for procrastination?

Regular coffee drinkers will have this feeling: make a cup of coffee in a coffee shop or make your own coffee without sugar or milk, but before long, the coffee will slowly cool, and the originally mellow coffee will also become sour and difficult to swallow. Why? Is the coffee not pure? Or the freshness of coffee beans? Can this situation be avoided? Isn't it pure? Or the freshness of coffee beans? Can this situation be avoided?

People who really understand coffee will have an understanding of coffee. In fact, drinking coffee is like eating fish. Very often, a hot fish is served fresh and delicious, but once cooled, the smell of the fish will become very strong, so coffee will have the same phenomenon. The reason why the coffee turns sour after cooling is that the coffee bean itself is a kind of fruit, so it is rich in tannin. When the coffee temperature drops, the tannic acid is released, and when the temperature is lower, the human taste is more sour, so we will obviously feel that the coffee has become sour after cooling.

Of course, not all coffee will turn sour after cooling. Generally speaking, the lower the roasting degree of coffee is, the more sour it will be, while many deep-roasted coffee will not become sour after cooling. And the better the quality of coffee beans, the smaller the difference in flavor between hot and cold.

So, if you want to keep your coffee sour, the best way is to drink it while it's hot. If it's really cold, you can try to add some light milk to make the sour taste less obvious.