Making a cup of coffee in the morning to start a new day has become a habit for many people. What's the taste of coffee? Some people think that coffee is bitter, others think that coffee is a combination of sour and bitter, and some others think that coffee is sweet. Why do people feel so different about the flavor of coffee? To this end, the Shanghai CDC shared a little knowledge about coffee. The flavor of coffee varies with the degree of baking. The baking degree of raw beans can be divided into light, medium and deep. The coffee beans with light baking have shorter baking time and higher acidity; Moderately roasted coffee beans are slightly sweeter than lightly roasted coffee, and their sweetness and acidity are relatively balanced; Deep roasted coffee beans usually taste stronger and bitter. Temperature affects the intensity of coffee flavor. Hot coffee, volatile aromatic substances are more active and produce strong aroma, which is the reason why many people fall in love with coffee. The flavor of coffee will deteriorate after cooling. If milk or sugar is added, it is easier for bacteria to breed. Therefore, it is recommended to boil and drink coffee immediately. High quality coffee should be finished in 5-20 minutes. The amount of natural substances extracted from coffee powder into solution (coffee solution) is affected by the temperature and storage time of coffee solution. The lower the temperature of coffee solution, the longer the storage time in low temperature state, and the more sour substances are dissolved; The higher the temperature of coffee solution, the longer it is placed in the high-temperature state, and the more bitter substances are dissolved. The length of time coffee beans are placed will also affect the coffee flavor, which will decrease with the extension of time coffee beans are placed. The freshly baked beans will slowly release carbon dioxide during storage, and the volatile substances will be taken away with them. The pleasant smell will also slowly disappear. At this time, the coffee will deteriorate. Meanwhile, the Shanghai CDC reminded that a cup of espresso prepared with 18G coffee powder contains about 60 ~ 80mg caffeine on average. The safe daily intake of caffeine is about 400mg. Considering the Maillard products produced by deep roasted coffee beans and the habits and hobbies of drinking coffee everywhere, it is recommended that the intake of coffee per person per day should not exceed 3 cups. (outlook new era)