A letter from our founder

I grew up with this soap in Japan. What is sold here under the same name is not the same thing.

My name is Mari Tanaka and I make Kakiyu. Before you buy another persimmon bar — from us or from anybody else — I want to show you what I check, and why so little of what reaches an American bathroom is the bar I grew up with in my grandmother’s.

Mari Tanaka Founder, Kakiyu · Written August 2026

A few years ago I flew home to Japan to see my mother, and within about a day of being back in the house I noticed it.

That specific smell. Not unclean — my mother is the most fastidious person I have ever met. She showers every day of her life. She irons things that do not need ironing. It was something else. Something I recognised without being able to put a name to it.

I said nothing. Not out of kindness — I could not think of one way to raise it that would not have taken something from her. So I said nothing for four days, and felt terrible about it the whole time.

My grandmother was the one who said it out loud

She lived twenty minutes away. She was eighty-seven then, and she belonged to the generation that simply says things. I ended up telling her — not really asking for anything, just because it had been sitting on me all week.

She was not remotely surprised. She just used the ordinary word for it — karēshū (加齢臭), which means something close to “aging smell”, and which is not a delicate term or a medical one. It is a word my mother would see on a bottle in an ordinary shop. In Japan this has a name, and everybody past a certain age knows it.

Then she got up, went into her bathroom, and came back with a bar of soap.

And I stood there holding it and understood that I had been looking at that soap my entire childhood.

Dark, a little austere, not the sort of thing you would ever pick up and examine. I must have walked past it ten thousand times as a child. I had never once wondered what it was for.

It is called kakishibu — 柿渋 — fermented persimmon tannin. Unripe persimmons, pressed and left to ferment for months, until what you have is a dark, astringent, nearly black liquid. Where I grew up, in Mino in Gifu, it is completely ordinary: used for centuries on paper, fabric, wood and skin, and nobody there would call it a product. Nobody had ever explained it to me because to my grandmother there was nothing to explain — and it had come within one generation of stopping there.

I did exactly what she told me. I left the bar in my mother’s bathroom, I said nothing, and I flew back to Seattle.

She has used it every day since. She has never mentioned why. Neither have I.

Then a friend asked me about her own mother

I moved to the United States at twenty-four, so by then I had been here long enough to know my friends’ parents. A few months after that trip, one of them brought it up with me — awkwardly, half apologising, the way you do when you are trying to say something about somebody you love. She had noticed it about her own mother. She had no idea how to raise it, or what it even was.

I recognised exactly where she was standing, because I had been standing there myself in the spring.

I still had two bars in my suitcase. I gave her one and repeated what my grandmother told me, word for word. Leave it in the bathroom. Don’t say anything. She’ll know.

It worked. She told somebody. Soon I was being asked for it by women I had never met — and when I went looking to buy more of it here, I found out two things.

The first is how many women are living with this and have no idea what it is. Nobody told them — not their mother, not their doctor, not one article until they went looking at two in the morning. Most had decided it was a hygiene failure, and were showering twice and three times a day trying to scrub off something that is not on the surface of the skin at all.

The second is that the bar I wanted to hand them is not sold here. Not really. There is no standard behind those two words — a bar built on concentrated fermented extract and a bar built on juice and orange colourant can print them in the same size type on the front of the box, and both are perfectly legal.

Which is why I ended up making it myself

That is the part that bothers me. Not the lost sales — we are small and new and I am not owed anybody’s money. It is the women who tried this, got a dyed fruit-scented bar, felt nothing after three weeks, and quietly gave up on the one thing that was going to help. The way my mother would have, if my grandmother had handed me the wrong one.

So I stopped trying to find it and had it made properly, at home. Kakiyu is produced in Mino — the town I grew up in — by people who have handled kakishibu their whole working lives. It is the same fermented extract that has been made there for centuries, at the concentration it is actually meant to be, rather than a trace of it dropped in so that the word can go on the front of a box.

It is made in small batches, because it has to be. Astringent persimmons ripen once a year, and there is only ever as much extract as that harvest gives. We make what it allows and then we stop. That is also why we run out sometimes, and I would rather say so plainly than pretend we have an endless supply of something that takes a year and a season to produce.

But do not take my word for any of it

I would rather hand you the tests than ask you to trust a stranger on the internet, so here are the six things I check. Most take under a minute. One of them takes ten seconds. Run them on our bar as happily as on anyone else’s — that is genuinely the point.

2

Read the panel — then ask how much

Turn the box over and find the ingredient list. You are looking for kakishibu, or the words fermented persimmon tannin. If what you find instead is “persimmon fruit extract”, or “fragrance”, or “parfum”, or there is no ingredient list at all — you have your answer, and you can stop.

But if it is there, you are only halfway. Because the second question is the one almost nobody asks.

How much of it is in there?

Fermented kakishibu is expensive. The fruit ripens once a year, it has to be pressed unripe, and then it sits fermenting for months before anybody can use it. That cost lands on whoever makes the soap — so the obvious move, and an extremely common one, is to put a token amount of real kakishibu into the bar, name it truthfully on the panel, and let the label do the rest of the work. Everything on the box is accurate. The bar still does nothing.

The panel tells you whether it is present. It does not tell you how much. So ask. Any brand carrying a real concentration will tell you the number without hesitating, because it is the most expensive thing they own. The ones that change the subject have answered you.

Ours is a 97% concentrated kakishibu extract, named on the panel, alongside exactly three other ingredients — green tea extract, camellia seed oil and glycerin. Those three are there for one reason: tannin is astringent, and without them a persimmon bar will dry you out. That is why so many cheap ones leave people itching.

3

Hold it up to the window

This is my favourite one, because it takes about four seconds and you cannot argue with the result.

Take the bar to a window and hold it up against the daylight.

A real glycerin-base bar is translucent. Light travels through it and it glows amber, like honey held up to a lamp, and you can usually see small bubbles suspended inside. That translucency is not decoration — it is simply what a glycerin base looks like, and glycerin is what holds moisture in your skin while the tannin lifts the odour off it.

A cheap bar is opaque. It is an ordinary soap base with orange colourant stirred through it. Light hits it and stops. It looks like a bar of soap that has been painted the colour of fruit, because that is exactly what it is.

Do not judge the shade, by the way — judge whether anything gets through. Kakishibu itself is nearly black. What colour it ends up in a finished bar depends entirely on the base it went into.

If no light gets through it, you are holding dyed soap base. Whatever else is in there, that bar was built to look like persimmon rather than to work like it.

4

Wet it and rub it on a white cloth

Run the bar under the tap and rub it a few times on a white cloth or an old flannel.

If a plume of orange comes off, that is added colourant, and it will keep coming off for the life of the bar. This is the single most common complaint on the cheap listings, and people are not exaggerating it — the reviews describe orange residue on soap dishes, orange runoff in the shower tray, and colour transferring onto bath towels that does not wash out.

A dye that bleeds onto cotton is also sitting against your skin twice a day. If your skin has become more reactive since menopause — and for a great many women it has — that is worth knowing before the third week.

A bar should clean the cloth, not colour it. If your washcloth is coming out orange, the bar is giving you pigment, not tannin.

5

Put it on the kitchen scale

Nobody thinks to do this, and it quietly decides whether you got value.

Marketplace listings advertise the number of bars. They are much quieter about the size of them. A great many of these bars come in well under what you would assume, which is how a “three-pack” ends up costing more per wash than a single full-size bar — and it is why so many reviews say the bar was half gone after two showers.

Kakiyu is a 100g bar, which is what you are looking at above. Weigh whatever you have against that. If yours is meaningfully lighter, work out what you actually paid per gram rather than per bar, and the bargain usually disappears.

Price per bar is the wrong number. Price per gram of soap you can actually use is the right one.

One last thing, and then I will leave you alone

You cannot audit your own smell. That is the whole cruelty of this particular problem — your nose adapts to you, so you are the last person in the building who can tell. It is also why the category is so easy to sell a useless bar into: nobody can immediately prove that it did nothing.

So give it two weeks and then ask someone who will actually tell you. A daughter, a husband, a sister. They will know before you do — mine did, and she never said a word.

And whatever you decide about us: before you buy another persimmon soap from anyone, run check number two. Turn the box over, find out whether the thing you are paying for is on the label at all — and then ask them how much of it is in there.

Mari Tanaka Founder, Kakiyu