Processing astringent American persimmons

I have Prok, but it has not fruited yet for me. Several others on here have reported the same problems you are having with Prok. My advice is to plant more.

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Yeah, that is the plan. I’ve got 10 rootstock trees growing in pots, preparing for grafts next spring. Also a Kassandra that I planted 4 years ago, which I hope will ripen fruit next year; and a Mikkusu that I grafted last year. It may take a few years, but I should eventually have some decent comparisons.

Maybe I’ll top work the Prok too.

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If you have the space just let it go. I would look into which varieties are coming of the tree without issue. Like I said my Meader came off perfect. Wilds tend to have a lot of astringency. Many people have reported varieties which had no astringency at all when ripe. It’s sad to hear that about Prok as I have it as well.

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I’m trying this approach on some apparently fully ripe but still somewhat astringent fruits. It’s been ~5 hours and the astringency seems gone. So that’s promising. But meanwhile, there are two problems:

  1. Baking soda (sodium bicarbonate) tastes salty. That saltiness impacts the flavor of the puree. For that matter, this amount of additional sodium isn’t ideal. Is there a low-sodium alternative?

  2. The puree, exposed to the open air, discolors dramatically. Right now, it is almost black. That’s not aesthetically appealing. Is there a good strategy for preserving the orange color?


Perhaps calcium carbonate. It is used in tums and also as a dietary source of calcium.

Try lime/lemon juice. It should also help in producing carbon dioxide as it reacts with the baking soda or calcium carbonate.

You’ll have to play with the quantities to find the optimum amounts.


Ahmad – Sounds promising. I especially like interaction of acid with carbonate.

Do you think it’ll matter that calcium carbonate is insoluble in water?

Edit1: How about Calcium or Magnesium Bicarbonate? I mention these only because they are supposedly soluble carbonates, though since posting I’ve learned that they do not exist in solid form. I’m not sure I can even buy them.

Edit2: If calcium reacts with lemon juice, do we get calcium citrate? It’s described as sour and salty. If magnesium, then mildly sour. But magnesium citrate is used as a laxative . . . .?


It has very low solubility in pure water, but it will dissolve (and react) to much higher extent in presence of acid.


Oh now this is fascinating.

He did mention this in the context of processing pulp for use in cooking, so I guess saltiness then can be compensated for out of the other ingredients. But for fresh eating…yeah. I guess trying much smaller amounts, and/or working through the list of other edible PH adjustors (add potassium bicarb to the list, though I hear that trades saltiness for bitterness)…

If the discoloration is from oxidation from the air and not the reaction itself, I would hope that immediately pouring the pulp into a ziplock bag and sucking most of the air out, and then tossing it in the fridge or freezer, might help…

  1. Yes, smaller amounts and/or other (bi)carbonates. Makes sense.

  2. The discoloration is apparently from oxidation in that it covers the surface whereas the inside remains orange-ish.

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Two assumptions: (1) Baking soda works by generating CO2. (2) Most tannins in a nearly ripe fruit are loaded in or near the skin.

If these assumptions are correct, maybe it would be way more efficient just to dump the sodium bicarbonate into a glass of lemon juice (or vinegar or whatever) inside a closed container that also holds the whole persimmons. That would generate CO2, surrounding the fruit.

Basically I’m wondering if mashing before treating shields much of the skin from any CO2 created by the bicarb.

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Hmm; well…technically the CO2 comes from the base directly ripping apart acids to get at those tasty oxygen atoms. So if it’s the reaction that’s directly neutralizing the tannins, you’ll probably need to mix it in. But if most of the tannins are near the skin…yeah it’s quite possible there’d be enough osmosis and such to react and neutralize enough acids near the skin to help with the flavor, and then the resulting CO2 would help ripen the intact fruit. Though worth noting: I would absolutely not recommend leaving a low-oxygen high-PH liquid at room temperature for long without talking to someone with a degree in food safety. Straight into the fridge or freezer in my uneducated opinion…

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@Itmaybejj – My understanding is that the CO2 (or alcohol vapor) produce an anaerobic environment that encourages reduction of ethanol to ethanal (aetylaldehyde), which then binds tannins. The acid-base reaction is just the source off the CO2.

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Inspired by @cdamarjian 's post last year of a CO2 chamber for euthanizing rats to feed to pet snakes, I made this set-up for removing astringency in kaki persimmons using an airtight plastic container and a paintball CO2 tank.

I can refill the CO2 tank at a local paintball store much more cheaply than buying Sodastream CO2 canisters.

I pick the fruit (Giombo in these pictures) when they are just starting to turn orange and still rock hard.

I put a few drops of bromothymol blue in water with a pinch of baking soda to make a basic solution and put the outlet hose into this glass. When the water changes from blue to greenish yellow, then I know the chamber is full of CO2 and stop filling it. I remove the CO2 tank hose and cover both the inlet and outlet with saran wrap to seal the chamber. I leave it for 3 days in a dark place. The fruit comes out firm and non-astringent.

The first time I tried it last year, I tasted the fruit immediately after removing them from the CO2 chamber and they tasted carbonated, like they had been soaked in soda water. They also still had some astringency. But after leaving them overnight, they were completely non-astringent and still firm.

After this treatment, astringent kakis have a texture just like fuyu-type non-astringent kakis, but I think they are sweeter and more flavorful. Most members of my household don’t really like the gooey texture of a ripe astringent kaki, but they love the crisp crunch of the CO2 treated fruit.

I also dry astringent kakis in a dehydrator, and if you slice them when they are just starting to soften up but still astringent, drying will remove the remaining astringency. It won’t work on hard, unripe fruit, though.


Here’s the youtube video describing how to build a CO2 rat euthanizing chamber that I followed to build my chamber: Co2 Euthanasia Chamber Build for Feeder Rats 2 - YouTube


I LOVE the fact that you followed up on my post from last year! This is definitely an improved set-up. The use of BTB and baking soda warms this elementary school science teacher’s heart. A++++


That’s a nice setup!


@cdamarjian @ncdabbler After treatment did you guys consume everything within 3 days? According to this study, CO2 treatment alone triggers the onset of post-astringency rapid softening. Persimmons lose ~60% of their firmness by day 3 after CO2 treatment (according to them). Did you notice anything (assuming they lasted that long)?

They mention treating with CO2+ 1-Methylcyclopropene to both rapidly remove astringency and prevent softening. 1-Methylcyclopropene is commercially available under the name EthylBloc and SmartFresh. It’s not an ethylene absorber. It binds to the ethylene receptor in tissue and prevents ethylene from having an effect. The study shows only a loss of ~20% firmness by day three with this treatment regiment.


I process only about 4 persimmons at a time …and end up eating all within 3 days (or maybe even all in 1 day!).
If you had access to a SmartFresh sachet, it would be interesting to include it with CO2 for a comparison test.
In this CO2 only method, persimmons are put in the bag/container in the rock-hard state and removed when they have slightly softened. Using SmartFresh might prevent this slight softening.

That may be an advantage if the intention is to refrigerate the astringent-reduced fruit for counter ripening later. In fact, maybe that’s what’s done to some specialty (astringent) persimmons that consumers just ripen on counter.
As usual, there are a lot of marketing practices to which the consumer is unaware!

Btw… “In the United States the National Organic Program does not allow the use of 1-MCP on organic produce” (Wikipedia)


I can’t find the post from last year, but I thought that was your suggestion to use the bromothymol blue! Maybe it was another responder to your post about the CO2 chamber. It wasn’t an original idea on my part. Anyway, thanks for inspiring young minds and not-so-young minds! :slight_smile:


@JustPeachy That’s an interesting finding, and it isn’t consistent with my own limited experience with CO2 treatment up to this point. I treated 2 batches last year (I made my chamber in November 2020 at the tail-end of persimmon season), and I just started my third batch this year. So that’s not a lot to go on. But each time I’ve treated persimmons this way, I’ve picked more unripe fruit than I can fit in my CO2 chamber. The ones that don’t fit end up in an open bucket next to my CO2 chamber. And each time, a couple of the untreated persimmons have been starting to soften after three days, while the fruit in the CO2 chamber is all still quite firm when I remove it. And we don’t eat all the treated fruit within 3 days. I’ve still had firm CO2 treated persimmons more than a week after treatment, and I haven’t put them in the fridge. I keep all my picked persimmons (treated and untreated) on my kitchen counter. Some of the treated persimmons do start to soften in the second week after treatment, and some of the untreated persimmons can go longer than that before they soften. But my general impression was that the untreated persimmons generally soften sooner. I need to watch more carefully with my current batch and record exactly how long it takes for them to soften. I suspect the time required to soften them has a lot to do with how close to ripeness the fruit were when picked. They were all starting to turn orange and rock-hard, but some were likely further along than others.