Gao Jian, director of Haishi Nutrition Society and deputy director of the Nutrition Department of Zhongshan Hospital Affiliated to Fudan University: In terms of nutrition, old hens are not better than young chickens, but the soup tastes richer and more delicious. This is because the nutrition of chicken mainly lies in the protein and fat contained in it. The content of these nutrients in old hens and young chickens is similar. However, due to the longer growth period of old hens, the creatinine, creatine, etc. contained in their meat The nitrogen-containing extract that produces the umami flavor is more abundant, so the stewed chicken soup has a richer and more delicious flavor. But these nitrogenous leachates do not have high nutritional value. It usually takes 1 to 1.5 hours to stew chicken soup. After that, the longer the stew time is, the nutritional content will gradually decrease. No matter how long the chicken soup is simmered, only 5-10 of the nutrients in the chicken will be dissolved in the soup, and most of the nutrients will remain in the chicken. Therefore, when eating chicken soup, it is wrong to discard the chicken. Many people are used to buying live chickens at the market, butchering them on site and making soup at home. They think the chicken soup tastes the most delicious. In fact, after buying fresh chickens, they should be placed in the freezer of the refrigerator for 3 to 4 hours before taking them out. Defrosting the stew will make the chicken soup taste more delicious. This principle is the same as not eating fresh fish: after the live fish is slaughtered, the muscle fibers of the fish gradually become stiff, and the protein in the muscle tissue cannot be broken down to produce amino acids, and amino acids are the main components of the delicious taste of fish. Only when the fish body gradually begins to transform from a high degree of stiffness to the autolysis stage, the rich proteins in the fish meat gradually decompose into various amino acids that are easily absorbed by the human body under the action of protease.