keep the persimmons in a sealed container at 20-25 C , then make sure that you have an inflow tube and outflow tube that can be closed properly (no leaks), fill the container with CO2 and check with CO2 meter, there are several types, get the container above 90 % CO2 and close the inflow and outflow valves. Astringency removal takes 1-3 days depends on variety and field treatments before harvest, in most varieties about 1 day.
Also apply 1-MCP if you wish the fruit to remain firm.
Thank you for your valuable feedback. Since controlled atmospheric condition is very expensive condition to create. Is it possible to replicate to do with low cost airtight chambers by releasing CO2 in it?
yes , you just need airtight chambers and add the inflow+ outflow valves, but you do need a way to monitor the CO2 levels, there are simple machines such as OXYbaby ( http://www.oxybaby.com/application/?gclid=CjwKEAjw47bLBRDkgorklobUklESJAAGH4-R96VCW_tb6CO5Kn-fISm6DLe5HFty5LCYvnsaJsOAeBoCKGvw_wcB ) that can be used for this type of work.
for a short period of time it will cause de-astringency and initial softening/progression in ripening (1-3 days, start with 1 day and check if astringency is removed), if kept in high CO2 for too long you may have CO2 damages (brown/green spots) and beginning of fermentation (increase of ethanol/acetaldehyde) from anaerobic metabolism.
Olives will keep well with little quality deterioration for up to 15 days in cold storage if the fruit is in perfect condition. Fruit quality can be maintained for longer periods with controlled atmosphere storage at 3% CO2 and 5% O2.
In: olive oil production by Paul Vossen.
To remove astrigency of persimmon fruit, please read the following article.