In a separate thread – https://growingfruit.org/t/persimmons-2021 – I asked whether CO2 or alcohol work equally well in Asian and American persimmons. Personally, I had very disappointing results with the American Prok. @Harbin responded with his observation that CO2 works with astringent Asians but does not work with Americans while hybrids are hit-or-miss, depending on genetics.
It would seem useful to compile results for various hybrid persimmons so growers can know when CO2 (or alcohol) might work. So if you have experience trying to reduce astringency in Asian-American hy bred persimmons, pease report your results.
I’ll do my part with Gora Goverla (aka Hoverla) and Gora Roman Kosh. Both these hybrids are very large (up to 300g) and are descendants of Nikita’s Gift backcrossed with kaki. So my rough estimate is that they are about 80 to 90 % kaki and 10 to 20 % virginiana. While Roman Kosh is very nice and juicy when soft. Hoverla turns into a mushy stuff which I don’t like.
So when I pick ripe and hard fruits of Hoverla I place them into a small cooler box. On the bottom of a cooler box is a small dish with 70% persimmon brandy (any spirits would do, I guess) covered with wire mesh. Fruits are loaded up to the rim covered with a lid and left there for 5 days.
After that they can be eaten while still firm, astringency gone whatsoever: crunchy, juicy nearly as good as the store bought Rojo Brillante.
Not sure if this is the right place for this, but I found reference to some additional wrinkles. Temperature seems to matter quite a bit, and it’s possible to overdo it (at least with some treatments) such that the tannins come back! This makes me wonder if instead of needing more time than kaki persimmons, virginiana actually need a shorter treatment.
Astringency was removed from‘Triumph’persimmons by immersion in water at 40°C for 5 hr or 60°C, for 1 hr. Similar treatments at 20° and 80°C, had no effect on astringency reduction. Subsequent application of 80% CO2 for 48 hr was effective for 20°C-treated fruit but not for 80° C-treated fruit, which became nonastringent only after exposure to acetaldehyde. Extending the 60°C treatment beyond 2 hr resulted in recurrence of astringency, which was not reduced by subsequent CO2 treatment. Astringency also recurred in CO2-treated non-astringent fruit, when exposed to high temperatures. The disappearance and recurrence of astringency correlated with amount of methanol-soluble tannins.
The possibility of the disappearance and recurrence of astringency did occur to me. Since Saijo is rendered non-astringent in an anoxic environment, would it reverse itself and return to astringency in open air?
The Saijo that I vacuumed for 4 days has remained non-astringent 2 days later in room air. Perhaps hybrids will react differently.
Perhaps someone with a hybrid can test the vacuum method.
Shimomura and Subhadrabandhu (1997) proposed a rapid astringency removal system by which the removal was achieved by treatment of 0.62-2.5 ml of 99.5% ethanol/kg fresh fruit and above 95% CO2 for 3-5 h at 40°C. The author suggested a sealed incubation of 12 h at 40°C after a temporary opening and chemical removing, and the fruits were stored at 20°C. The treated fruits remained unripe and had a “crisp” texture for a long period.
As I understand it, Triumph is an astringent Asian type, developed in Israel and sold commercially after treatment with CO2 under the name Sharon. So while this article is interesting, it doesn’t move the ball forward re American fruit.
I agree it doesn’t have the answer for American and hybrid persimmons, but it does suggest some factors that I don’t think have been adequately tested. In particular, the fact that it can be overdone is very interesting.
I’ve had no real luck trying to remove astringency from Nikita’s Gift with CO2 this year.
Did 24hrs of CO2 in a sealed homebrew keg at room temp followed by 3 days in normal air, still astringent. Then repeated that process and they do seem less astringent but still not really edible and who knows if that is the CO2 or just the time.
After the first CO2 treatment I also took a few fruits and put them in a bag with an apple and one of those has softened and fully reddened to a usual edible state at least.
I’m still at least 2 years out from being able to test this myself, but I’ve put together a list of protocols to test out with hybrid and American persimmons that address some aspects that I don’t think have been properly tested yet. Note that both the times and temperatures are important. So far, I’ve seen people focus more on which chemical(s) to add, or a yes/no on CO2, immersion, etc. What I haven’t seen is paying close attention to what the temperature is and how long the treatment lasts. I also haven’t seen anyone test adding acetaldehyde directly (probably because it’s hard to get if you’re not a lab or school). Artificial green apple flavoring may be an acceptable substitute.
Sealed container with CO2 and ethanol for 3-5 hrs at 40°C 2. Sealed container with CO2 and acetaldehyde for 3-5 hrs at 40°C 3. Sealed container with CO2, ethanol, and acetaldehyde for 3-5 hrs at 40°C
40°C Water bath for 5 hrs
60°C water bath for 1 hour
60°C water bath for 1/2 hour 7. 40°C Water bath for 5 hrs, sealed in bag w/acetaldehyde
40°C Water bath for 5 hrs, sealed in bag w/ethanol 9. 40°C Water bath for 5 hrs, sealed in bag w/acetaldehyde & ethanol 10. 60°C Water bath for 1 hr, sealed in bag w/acetaldehyde
60°C Water bath for 1 hr, sealed in bag w/ethanol 12. 60°C Water bath for 1 hr, sealed in bag w/acetaldehyde & ethanol 13. 60°C Water bath for 1/2 hr, sealed in bag w/acetaldehyde
60°C Water bath for 1/2 hr, sealed in bag w/ethanol 15. 60°C Water bath for 1/2 hr, sealed in bag w/acetaldehyde & ethanol
Edit: Upon further research, working with acetaldehyde is not something we can safely do at home. I’ve left them in the list for reference, but those tests will have to be left to research professionals.
I came up with these procedures to test based on several research articles on removing astringency. Yes, all the articles are about kaki, but they do provide some interesting clues. The water bath ones would be easy to run concurrently for a given temperature, especially if you have a sous vide circulator. If anyone wants to try these out, please let us know how it goes. If not, hopefully you’ll be hearing from me in a couple of years!
Acetaldehyde is the immediate precursor to ethanol in fermentation. Like diacetyl, acetaldehyde is found in large quantities during early fermentation as the yeast produces it en masse early in their metabolic cycle. If there is a high amount of dissolved oxygen present in the young beer, then the oxygen could react with ethanol and oxidize it back into acetaldehyde. Edit: looks like I was wrong. Some cursory searching shows that while acetaldehyde does have a green apple flavor, a different compound is actually used in artificial flavoring. Acetaldehyde treatment might have to be left to the pros.
Has anyone tried using a container of yeast in sugar water as their CO2 source in a container? It would produce CO2, acetaldehyde, and ethanol, along with a myriad of other compounds that may or may not have an impact.
@jcguarneri I have lots of Nikita’s Gift fruit at about the right stage to do some testing. I could try adding yeast and sugar water to my CO2 setup and see if that helps remove astringency from NG fruit.
For some of your other ideas, I don’t have a water bath, but I have an aquarium heater I could put in a tub of water, but I probably couldn’t even get to 40 deg C with that. Do you think the temp in a crock pot would be stable enough to try a small batch?
Nice! A crock pot might get too hot, but it’s worth a try. An easier method would be to use a cooler. You’d have add water that’s a couple degrees warmer (to account for heat loss to the fruits and cooler). An average cooler should be able to hold close enough to 60C for an hour or 40C for 5 hours. I used to hold similar temps in an average cooler doing all-grain homebrewing, and people will use coolers for low-tech sous vide. A higher-end cooler (Yeti, etc). would be even better, but probably not necessary.
Beats me! I really wish I knew. I can’t even guarantee that a given green apple flavor would have any acetyldehyde in it, but my understanding is that most if not all would contain it. Acetaldehyde is the key part of that “apple” flavor. I suspect it wouldn’t take much, maybe a few drops.
Edit: looks like I was wrong. Some cursory searching shows that while acetaldehyde does have a green apple flavor, a different compound is actually used in artificial flavoring. Acetaldehyde treatment might have to be left to the pros.
I really should read the paper to which you were referring to answer my question, but I’ll pick your brain since you’re making good suggestions -
Is your understanding that the hot water bath supposed to accelerate the reactions and result in faster removal of astringency, or are some of those reactions only likely to occur at all at a warmer temp?