I’ll have to see if I can find the full text for these articles, but the abstracts are interesting.They’re looking at removing tannins from kaki persimmons, but I think they illustrate the key to understanding this whole thing. First, the tannins don’t actually go away, they just become insoluble. Second, they don’t dissipate right away, regardless of treatment type, but rather go down over time. So, if there’s more tannin to become insoluble, it should take longer to work through. I’m still trying to find some numbers on this, but I’d bet money that D. virginiana fruits are starting with a higher tannin concentration than kaki fruits. If that’s the case, it follows that any treatments that work for kaki should work for virginiana, but I would expect it to take longer. @cousinfloyd does that seem plausible to you? It certainly explains why I have limited luck freezing out the tannins from Hachiya; I’ve probably never left them in long enough. Also, the dehydrator probably just happens too quickly for the tannins to become insoluble for virginiana.
It sounds like ethanol, CO2, and submerging in water are all working on the same principle: creating anaerobic conditions that make the fruit accumulate acetaldehyde (green apple smell), which then reacts with tannins. So find a way that works for you to make an anoxic environment. Or maybe toss them in a bag with a green Jolly Rancher…
@jrd51 if my general thesis holds water, your frozen pulp should reduce in tannins the longer it sits in the freezer. Also, since it’s about concentration of soluble tannins rather than simply presence or absence, there’s probably a ratio of fully ripe to underripe persimmons where the concentration stays low and your batch isn’t ruined. The trick is if we’re talking 10:1, 100:1, or 1,000:1.
Comparatively, higher soluble tannin content 11.68 (mg/g DW) and lower insoluble tannin content 10.02 (mg/g DW) was observed in control (day 0). Therefore, the astringency of persimmon fruits incubated at − 20 °C and − 80 °C was markedly reduced and after 15 up to 60 days of storage, the astringent taste virtually disappeared.
In the last century, several postharvest treatments including ethanol vapour, carbon dioxide gas, nitrogen gas or warm water treatment have been assayed to remove astringency without fruit softening. Under anaerobic conditions, fruit accumulate acetaldehyde, which reacts with soluble tannins transforming them into an insoluble and non-astringent form. Persimmon tannins, mechanism of astringency loss, deastringency treatments, and factors affecting the process of astringency removal are examined.
https://link.springer.com/article/10.1007/s13197-020-04818-3#:~:text=The%20astringency%20of%20persimmon%20fruits%20can%20be%20removed%20by%20the,1a%2C%20b).
https://www.researchgate.net/publication/287313729_Tannins_of_persimmon_fruit_Artificial_removal_of_astringency