Thanks. But on reflection, I’m not sure that this particular issue – a test – is more than academic. The test is useful to scientists as an objective method for measuring astringency. But would I ever use it?
With apples, I feel that I can “starch test” a few apples and then, if the starch is low, pick the whole tree. It won’t matter if one apple is 2% starch and another is 5%. I wouldn’t notice the difference and a cider combining the apples would be quite acceptable.
With astringent American persimmons, I may test one that is low in tannins while its untested neighbor is just high enough in tannins to be inedible. After all, the taste threshold for astringency is low, and the fruit don’t become fully ripe all at once.
Also, there’s a version of the “uncertainty principle” at work. I can only eat the fruits that are untested. Once I test a fruit, whether it’s ripe for not, I have to discard it. How many good persimmons do I want to throw away?
Bottom line: I may end up using some treatment (probably alcohol or CO2) on all my whole American fruit. And I will almost certainly end up using some treatment (alcohol, protein) on any puree or paste that I make.
Continuing, it occurred to me that if acetaldehyde is the “active ingredient” that binds “kaki tannin” then maybe I should simply add it directly to any puree.
The problem is that while acetaldehyde is produced naturally in fruit and is rapidly metabolized by the human liver, it can be toxic. It is, for example, one of the substances responsible for a hangover.
It might also work to add small amounts of ethanol directly to a puree, then rely on still active enzymes to dehydrogenate the ethanol to produce acetaldehyde. But I don’t want the persimmon paste to taste like alcohol; and I don’t want more acetaldehyde than would be necessary to bind the tannins. The precise method would be to titrate the doses, but that’s just not practical.
I’m left thinking that the easiest and safest approach might be to find a tasteless, harmless protein (like the soy milk discussed above) that will bind the tannins. Probably I could use a combination of crude arithmetic and trial-and-error to derive some appropriate dosages.
I agree it’s probably not very practical. If you really wanted to, though, you could cut off a small piece of a fruit and test that, leaving the remaining fruit usable. I think it would be most useful, though, for evaluating your treatment results. I think, though, that the taste test would be good enough.
If you’re looking for a source of acetaldehyde, look no further than green Jolly Ranchers. Acetaldehyde is green apple flavor. I bet one JR would have enough, and it’s clearly a safe dose. However, the catch is the reaction probably happens faster at room temps, and your puree would be very vulnerable to spoilage, fruit flies, etc, if you leave it out to react.
Another possibility: try the ethanol + whole persimmons in sealed container, plus dissolve a green JR in the ethanol for good measure.
Edit: I know most of this isn’t really practical, but I really enjoy shaking the wacky theoretical branches to see if anything useful falls out.
LOL. Yes, acetaldehyde is also the green apple flavor in some white wines. It can be viewed as a bug or a feature! But these examples are helpful in showing that we shouldn’t worry about acetaldehyde too much if we can keep the dose low.
I’ve thought a little bit about spoilage. If the issue is yeast, then the result of fermentation would be more ethanol (and hence more acetaldehyde) in the persimmon paste. We just wouldn’t want 7 days of fermentation. Unfortunately, KMB (which is a common antidote to wild yeast in brewing) reportedly retards the removal of astringency.
If the issue is mold or bacteria floating in from the air, I think it might be adequate to (1) keep the container closed, which is standard practice; and (2) rely on alcohol vapor to keep the closed container sterile. Even if alcohol isn’t the main method used to remove the astringency, it seems there’d be no harm (maybe help) in spraying a mist of alcohol into the container before closing.
I’m assuming that the soy milk method is fairly fast, depending mostly on the thoroughness of any mixing. If so, that’d be another advantage. I haven’t been able to read anything more than the abstract of the relevant article, but I’ve requested a copy of the full report from the author.
More info. Plants produce tannins specifically to render leaves, unripe fruits, and/or seeds unpalatable to predators, both insects and mammals. Tannins interact with proteins in saliva (and elsewhere). What we experience as astringency is the precipitation of the insoluble combination of proteins and tannins. Apparently, the reactive proteins are high in the amino acid proline. Well, technically it is not an amino acid, but that may be TMI. The presence of proline causes a structure of the PRPs that promotes binding with tannins.
Hypothetically, one strategy for neutralizing astringency in a persimmon paste would be to add proline-rich proteins (PRPs) such as those found in saliva. The condensed tannins that cause astringency in persimmons would bind with the PRPs, precluding any further interaction with PRPs in the actual saliva of anyone eating the paste. But as far as I know (?), I can’t easily acquire authentic salivary PRPs.
In wine-making, gelatin (derived from animal collagen) is used to remove harsh astringency. Gelatin is also comprised of proteins that are rich in proline – not as rich as salivary proteins, but maybe rich enough for our purpose. So:
I’m going to experiment with using gelatin to neutralize astringency in persimmon paste.
If anyone has any helpful comments, please weigh in. In particular, I’d be interested in knowledgeable insights about either (a) gelatin as a tool for binding condensed tannins, or (b) other proline-rich proteins that might work.
There is a lot of proline (~4%) in soy isolate – the protein powder you might buy at GNC. But as I understand it, that proline is not combined with other amino acids in molecules of protein.
Presumably there is also proline in the proteins in soy milk at roughly the same concentration (excluding the water). Those proteins could be responsible.
By comparison, gelatin is roughly 12% proline. Salivary proteins are 25-40% proline.
So far, my effort to produce an edible puree has been an abject failure.
Mashed, mostly ripe, but still somewhat astringent Prok (not Asian) persimmons can produce a nearly palatable starting mash.
But then adding alcohol directly to the puree does not eliminate astringency, even after 2 days. I thought maybe the enzymes that drive the conversion of ethanol to acetaldehyde, which then binds tannins, would work “in vitro.” I’ve seen scant evidence that it does.
And then adding gelatin similarly has a modest apparent benefit, if any. I thought that the high-proline proteins in gelatin would bind complex tannins. This reaction occurs instantly in saliva. Again, I’ve seen scant evidence for it in a pot.
Heating the mix doesn’t help.
So far, the results have been consistently disgusting. The texture is mealy. The taste is still astringent. And if anything, the taste is less sweet that the starter mash.
That’s not good news.
Joe – does Prok not fully ripen in your location?
I am getting several H63a already dropping. It may be a good candidate for you. I had Early Jewel also ripen a full crop last year. Both are excellent tasting.
Of course, by the time they drop, they are fully non astringent.
@ramv —. Prok appears to ripen fully. I’ve been harvesting them off the tree and the ground for 2 weeks. It’s 73 F today (and has been similar for many days) and if I find the energy to hobble down there on crutches, I’ll harvest some more today or tomorrow.
BUT — often / usually the fruits are not 100% non-astringent. You can counter that they are then not fully ripe but they are orange, soft, dropping on their own or detaching with a gentle tug. So they are ripe in the obvious respects, but not totally free of astringency. Also I would describe them as only mildly tasty and mildly sweet.
I think that next year I will thin the fruit to see if that helps with flavor and sweetness. But I’m not optimistic that it can help with astringency. Hence I’m trying ways to attack the astringency artificially.
p.s. I’ve got 10 rootstock trees growing in pots, destined for grafting net spring. H63A is a top selection on the current wish list.
I just let them spend a while on the counter. Sometimes a week or more. Unless you have a ton of persimmons, it is hard to get a batch to ripen at the same time.
I haven’t tied it. I assumed not, because very soft fruit that drops off the tree is still often astringent. So I started to try the alcohol method on them.
I seem to be able to get not-quite-ripe Prok persimmons to become ripe and non-astringent after a few days in alcohol vapor. Based on what I said above about “ripe” fruit, I have assumed that a few days in air (no alcohol) wouldn’t be enough. But I could be wrong and need to test it.
I’ve written up my effort with whole fruits in a separate thread. Here I’m trying to document my attempts to remove the astringency from a puree made by crushing the same not quite non-astringent fruit. It’s two threads – one about whole fruit, one about puree.
Your comments are very welcome. I don’t mean to discourage. I just wanted to clarify that I started one thread on whole fruits, one on puree.
Happen to have Lee Reich’s “Uncommon Fruits for every garden” out of the library…he mentions that astringency in pulp can be removed by adding “half a teaspoon of baking soda for each cup of pulp.”
My American tree is a baby so I can’t test this yet… anybody tried it?
I think a lot of the astringency depends on the variety. The meader I have the fruit comes off the tree with no astringency while some of the wilds take a week or two on the counter to get rid of it. Others never seem to lose all of it.
@Robert – My only experience is with Prok, so I’ll take your word for it. I just didn’t expect this very popular variety to be a problem. I wonder if growing conditions make a difference, especially weather.