Persimmons contain a lot of tannins, called tannin cells. Tannin cells in astringent persimmons are mostly soluble tannins. When people eat persimmons, some single cells rupture, soluble tannins flow out and are dissolved by saliva, which makes people feel strong astringency. Tannin cells in sweet persimmon are mostly insoluble tannins. When people bite persimmons, tannins will not be dissolved by saliva, so they will not feel astringent. The so-called astringency of persimmons means changing soluble tannins into insoluble tannins (that is, storing persimmons in a sealed container for a period of time), not removing or reducing tannins ... Put persimmons in a clean container, soak them in warm water of 40 ~ 50 degrees, seal the container from the air, and keep the temperature for about 24 hours. The exact time is related to many factors. The success of astringency can only be judged by the taste, and it tastes sweet and crisp. Persimmons with lower maturity usually need to be soaked for a longer time. The method of removing astringency with warm water is summarized by northerners in practice. The difficulty of this method lies in keeping warm, and the water temperature must be kept at 40 ~ 50 degrees. However, many families now have yogurt machines. We can keep persimmons warm in a yogurt machine, which is simple and convenient. Low temperature will lead to longer soaking time. For example, southerners like to soak in cold water, although the astringency can be finally removed, the soaking time is as long as 4 ~ 7 days. High temperature will not only lead to peel bursting, but also make persimmon peel brown and pulp waterlogged. Worse, it will inhibit or kill the enzymes in persimmon, leading to the failure of astringency removal, which is what people call "cooking" dead persimmon. If the water temperature can be kept at 40 degrees, it is the most ideal temperature for warm water to remove astringency, that is, persimmon will not be damaged, and the activity intensity of enzyme substances is also in the highest state, with the best astringency removal effect and the shortest time. Another disadvantage of warm water astringency removal method is that the taste of lazy persimmon is slightly weak, and it can only be stored for 2 ~ 3 days at most, and the color will turn brown after a long time.