The Mushroom That
Cannot Be Farmed

In a good year matsutake is among the most expensive foods on earth. It is not especially nutritious. It is not rare in the way a truffle is rare. It is firm and a little woody and, by the standards of the mushrooms people eat for pleasure, unremarkable to chew.

The entire price is for a smell.

That is not a flourish. It is what the trade is organised around. Matsutake are graded on aroma before anything else; they are picked at the button stage, before the cap opens, because the smell is strongest then; they are flown rather than shipped; and the same mushroom that commands a fortune fresh is worth a fraction of it a few days later — not because it has spoiled, but because it has stopped smelling like that.

Anna Tsing spent years following this mushroom around the northern hemisphere and opens her account with the smell rather than the money. Her word for the aroma is the autumn aroma, which is the phrase Japanese poetry has used for it for centuries: not a flavour note, a season.

So the object at the centre of this economy is not an object. It is a volatile compound leaving a surface, and something on the other side detecting it.

Which raises a question the price makes urgent. If the entire value is the smell, and the smell is what people disagree about — then where, exactly, is the thing being paid for?

The autumn aroma is not mysterious at the chemical level. It has been pulled apart by gas chromatography and it has names.

Two compounds dominate the volatiles that matsutake mycelia and fruiting bodies put into the air: 1-octen-3-ol — the compound most people would call “mushroom” if asked to name the smell of mushrooms — and methyl cinnamate, which is sweet and spicy and is the part that is not like other mushrooms at all. Around them sit 1-octen-3-one, 3-octanone, 3-octanol, benzaldehyde, phenylacetaldehyde, linalool, methional and others, each contributing at its own threshold.

The grading practice turns out to be chemistry rather than superstition. As the fruiting body ages, methyl cinnamate and 1-octen-3-ol both decline. The mushroom is not degrading into something unpleasant; it is emitting less of the two things it was being bought for. A price that falls with the hour is tracking a measurable quantity.

So far this is a tidy story about an object with a property. A mushroom emits molecules; the molecules are the smell; the smell is the value. Every step of that sentence is wrong after the next spread, and it is wrong for a reason that has nothing to do with mushrooms.

The forest is full of things that meet these molecules, and they do not agree about them even slightly.

Deer choose matsutake over other mushrooms. Bears turn over logs and dig ditches for it. Oregon pickers told Tsing about elk with bloody muzzles from driving their faces into sharp pumice soil to get at it, the smell taking them from one patch straight to the next. Flying insects circle underground caches the way they do over truffles.

And in the same soil, meeting the same compounds:

One set of molecules. An elk digs until it bleeds. A bacterium leaves. Nothing about the molecules changed between those two sentences.

It is tempting to file this as a difference in taste — the elk likes it, the slug does not, animals are different. That reading is comfortable and it is the wrong shape. The elk and the slug are not weighing the same experience and reaching different verdicts on it. They are not having the same experience.

There is a laboratory version of this, and it is blunt: 1-octen-3-ol and methyl cinnamate have been shown to repel a mycophagous springtail — an animal that eats fungi — away from the fungus producing them. The compound we grade and fly across the world is, to something six millimetres long, a keep-out sign.

Here is the settled fact this whole zine rests on, and it is ordinary sensory biology rather than anything contentious.

A volatile molecule leaves a surface and drifts. If it reaches a nose, it has to fit — physically fit — into a protein sitting in the membrane of a sensory neuron. That protein is an odorant receptor. If the shape works, the receptor changes conformation, the neuron fires, and a signal goes to the brain. If the shape does not work, nothing happens at all. Not a faint smell. Nothing.

Humans carry about 400 intact odorant receptors. Any given molecule activates some combination of them, weakly or strongly, and what we experience as one smell is the pattern across that combination.

The smell is not in the mushroom. It is in the meeting — and the meeting needs both halves.

Which means the question “what does matsutake smell like?” is incomplete in the same way “how heavy is this?” would be incomplete without saying in what gravity. It smells like whatever it produces in the receptor array it lands in. Change the array and you change the smell, without touching the mushroom.

The elk and the soil bacterium have wildly different arrays, so it is no surprise they end up somewhere different. The interesting question — the one with a number attached — is how different the arrays are between two people.

This is the spread the zine exists for, and the reason it is filed under a settled fact rather than a nice idea. Somebody went and counted.

Mainland and colleagues screened human odorant receptors in a laboratory assay, found which molecules switched them on, and then asked how often the ordinary genetic variation between people actually changes whether a receptor works. The abstract states the results plainly:

Over thirty per cent. Not in exotic cases. Not between distant populations. Between any two people, on average, roughly a third of the equipment differs in ways that change what the equipment does.

And they checked it against actual perception rather than stopping at the bench. Variation in one receptor, OR10G4, explained over 15% of the variation in how intense people found the smell of guaiacol, and over 10% of how pleasant or unpleasant they found it.

Two people standing over the same mushroom are not running the same instrument. That is not a metaphor for anything. It is a measurement of protein function.

The general figure is striking. The worked example is the one that is hard to argue with, because it goes all the way from a letter of DNA to a word a person says out loud.

Androstenone is a steroid derived from testosterone. It turns up in sweat, in pork from uncastrated boars, in truffles. Keller and colleagues open with what people report when they smell it:

Foul, lovely, or not there. Three people, one bottle.

Then they found the mechanism. A single human receptor, OR7D4, responds to androstenone and its relative androstadienone — and to essentially nothing else, having been tested against a panel of 64 other odours and two solvents. A common variant of that receptor carries two amino acid substitutions, R88W and T133M, which severely impair how it works in the dish.

People carrying the impaired version were, as a group, less sensitive to both steroids and found them less unpleasant. The genotype accounts for a significant share of both how strong the smell seems and whether it is horrible.

So the argument about whether androstenone stinks was never an argument about androstenone. It was two proteins, differing at two positions, doing different things — and each person accurately reporting what their own equipment returned.

Nobody in that room was wrong. There was no fact of the matter about the smell to be wrong about.

Now the mushroom again, with the mechanism in hand. Tsing is unusually direct about the smell for someone who wrote a book in its praise, and her honesty is the thing to keep.

Read that against the last two spreads and it stops being a remark about taste. Some people liken it to rotting things and some to clear beauty is exactly what you would predict of a complex volatile mixture landing in receptor arrays that differ at a third of their alleles.

The usual framings for that disagreement are all available and all wrong in the same way. An acquired taste. A cultural preference. You have to learn to appreciate it. Each of them assumes one smell is arriving and people are responding to it well or badly — that there is a correct experience, and a distance from it that can be closed with effort or breeding.

There may be no distance to close. If the arrays differ, the smells differ, and the person who says rotting things may be reporting their own arrival accurately and completely.

There is a second thing about matsutake that will not sit still, and it sits directly underneath the first.

Nobody can farm it. Not for want of trying: Japanese research institutions have put decades and enormous sums into it, and the most recent review of the field still opens with the verdict that cultivation “has been mostly unsuccessful.” Commercial supply is still people walking into forests.

The reason is that matsutake is not a self-contained organism. It lives in a transformative mutualism with the roots of particular trees, taking carbohydrates from the pine and foraging for it in return — and the field successes that exist were achieved using trees the fungus had already colonised, then waiting years. The only known way to farm it is to already have the relationship.

Set the two facts side by side, because they are the same fact at two scales:

Both halves of this economy are relationships that somebody has mistaken for objects. The mushroom is not a product with a yield; it is the visible few days of an exchange decades old. The smell is not a property with a value; it is what happens when that exchange’s by-product meets a particular array of proteins.

You cannot farm the first. You cannot standardise the second. It is the same refusal, twice.

Everything above is chemistry and protein function. Here is what it does not license, and then what it does.

It does not license everyone has their own truth. The variation here is the opposite of that: it is public, physical and measurable. You can sequence the receptor. You can express it in a dish and see what binds. Two people disagreeing about androstenone is not a breakdown of objectivity — it is an objective fact about two different proteins, and the disagreement was predictable before either of them opened the bottle.

What it does license is narrower and harder. When someone reports a sensory experience you do not share, “you are exaggerating” and “you will get used to it” are not the modest, sceptical positions. They are the extravagant ones. They require that one receptor array be the real one and the others be errors relative to it — and no such array exists. There is no reference nose kept in a vault in Paris.

“Normal” here is a statistic about a population, not a fact about a person. It tells you where most of the alleles fell. It does not tell you what arrived in anybody.

Those of us who are Autistic hear the correction constantly, and rarely about mushrooms. The lights are fine. The shirt is fine. Nobody else can hear that. The last of those is often literally true and is being offered as though it settled something. It does not settle anything, because the question was never whether the room is loud. It is what arrived.

The universe does not run a reference implementation of a nose. It just makes receptors, and they vary, and every one of them reports honestly.

We love you down to your star stuff — not because the chemistry says so. The chemistry says nothing about who deserves what; it never has and it never could. Down to is not because of. What the chemistry removes is only an excuse: it takes away the pretence that there was a correct experience you were failing to have.