What is the thing that floats on the water after the pig's trotters are cooked in water? (yes! ! )

There will always be such floating foam in succulent soup. This is blood and other impurities. If you take it out in time after boiling, the soup will not be like this. The succulent vegetable soup in the hotel is blanched first to remove the floating foam, so that the soup is beautiful and the nutrition is lost. Ordinary dishes are cooked at home, the water is boiled, and the floating foam is taken out at the beginning, and it will be fine.