How to ferment green soybean milk into sour pulp

Soak mung beans in cold water for 10 hour, add water and grind into paste, then add slurry and cold water to filter, and put the filtered slurry into a cylinder. The top layer is grayish green, that is, raw bean juice. Skim off the foam and slurry, then add cold water and boil it into bean juice. The bean juice made that day is sweet, the next day is sweet and sour, and the third day is sour, that is, sour pulp. The so-called acid is the juice discharged after making tofu with brewed white vinegar for the first time, commonly known as pulp. Yogurt is a unique food in Beijing, which has a strong rancid smell and is difficult for ordinary people to adapt to. Those who don't like to drink will say that they are like swill and sour; Love to drink will sour, just like stinky tofu.