What are the common methods for removing astringency from persimmons?

For traditionally cultivated persimmons, most cannot complete natural astringency removal on the tree, and must undergo artificial astringency removal treatment after harvest before they can be eaten or processed into dried persimmons. These persimmons that can only be eaten or processed after artificial astringency removal are called astringent persimmons. There is also another type of persimmon that can only complete natural astringency removal when it has a relatively large number of seeds (at least 3 or more); when there are few or no seeds, it cannot remove astringency naturally. This type of persimmon tree is a non-complete sweet persimmon.

If the variety grown is an astringent persimmon, it must undergo astringency removal treatment before it can be eaten or made into processed products; if what is grown is a non-complete sweet persimmon, pollinator trees must be arranged so that it is fully pollinated, forms many seeds, and produces many brown spots in the flesh before it can remove astringency naturally.

For astringent persimmons, even after the fruit ripens, it still contains a large amount of soluble tannins, and eating it gives a strong astringent taste. If artificial methods are used, astringent persimmons can be de-astringed in a short time. Several simple and practical methods for removing astringency from persimmons are introduced below:

1. Warm water astringency removal method: Put the persimmon fruit into a container filled with 35-40°C warm water, cover the mouth of the container tightly with a cotton quilt, seal it and keep it warm, and after 15-30 hours the astringent persimmons can be de-astringed.

2. Lime water astringency removal method: Prepare it in a ratio of water:quicklime of 10:1, put the persimmon fruit in when the lime water is lukewarm, using just enough to submerge the persimmon fruit, stir gently, then seal the mouth of the container, and after about 3-4 days the persimmons can be de-astringed.

3. Mixed storage astringency removal method: Mix the persimmon fruit with a small amount of ripe apples, pears, kiwifruit and other fruits (the amount used is about 1/10 of the persimmons), place them together in a container and seal it. Use the ethylene produced by the other ripe fruits to promote astringency removal in the persimmon fruit. Under conditions of 20°C, good astringency removal can be achieved in 3-7 days.

4. Alcohol astringency removal method: Place a layer of cotton at the bottom of a sealed container, then put in the persimmon fruit. Arrange the persimmon fruit in layers, spray each layer with a certain amount of alcohol or liquor, and then seal it. For every 20 jin of persimmon fruit, use 80-100 ml of alcohol or liquor diluted to 35%. Under conditions of 20°C, astringency is generally removed after 5-8 days.

5. Carbon dioxide astringency removal method: Seal astringent persimmons in a container or plastic bag so that the ratio of fruit volume to remaining space is 1:1.29. Relying on the carbon dioxide produced by the astringent persimmons themselves, increase the carbon dioxide concentration in the container to above 60% and lower the oxygen concentration to below 1%. Under conditions of 20°C, astringency can be removed within 3 days. When persimmon production is large in scale and high in yield, high-concentration carbon dioxide treatment is often used to remove astringency from persimmons. Persimmons packed in boxes or baskets are sealed inside a plastic greenhouse film tent, and compressed carbon dioxide gas is injected from a steel cylinder. When the temperature is 25°C and the concentration reaches above 60%, astringency can be removed in about 24 hours.

6. Ethephon astringency removal method: Use 250-500 mg/l of ethephon liquid, add 0.2% laundry detergent as a spreading agent, spray or dip the fruit, and in about 3-5 days it will soften and lose astringency.

In addition, astringent persimmon trees can be improved through top grafting to change varieties. After top grafting to change varieties, the persimmon tree can restore its canopy in the same year and restore yield in the second year, making it an effective method for improving astringent persimmon trees. However, when top grafting to change varieties, attention should be paid to the following issues: high-grafted varieties have strict requirements for the interstock (the tree that needs top grafting). Jiro-line varieties have good compatibility with most interstocks and grow and bear fruit well; Gosh-line varieties have a high survival rate in the year of grafting, strong growth vigor, and a large number of flower buds formed, bearing a large amount of fruit in the second year, but afterward their growth vigor gradually weakens until they die; Fuyu-line varieties have relatively good compatibility with wild persimmon and some astringent persimmons, and grow and develop normally, while with other rootstocks the survival rate is low, and after survival the growth is weak, or they even wither and die in summer. Therefore, in production, when top grafting to change varieties, the combination of varieties and interstocks must be selected and matched reasonably. At present, varieties with relatively good overall traits include Jiro, Okitsu, Xinqiu and others, which can be selected for cultivation.