Straw

Oysters run on pasteurised straw because the heat lowered the competition, not because it erased it.

Why straw is pasteurised and not sterilised

Straw is a dead stalk, rich in cellulose, poor compared with grain, full of air if you do not crush it. In the field it carries bacteria, moulds, sometimes insect eggs, dust. To give it to an oyster you do not need a biological void. You need a lowering. Pasteurisation is that lowering: a heat that kills most vegetative forms and lets a minority of tougher organisms live on, often in low numbers. The oyster, Pleurotus, is aggressive. It sets off from grain spawn that is already colonised, numerous, and it occupies the straw before that minority reorganises. The race is real. It is not a formality.

Sterilisation is a different contract. Steam around 121 °C, endospores included, a substrate that comes out with almost nobody in it. It makes sense on wood, especially if there is a supplement, because shiitake and lion’s mane are slower and a wood that is sterile-but-rich does not forgive a competitor. On straw, sterilising and then opening in the kitchen is often worse than pasteurising. You have removed even those few organisms that were taking up space, and you have left a bare food for whoever arrives with the dust. The oyster can still win, if the spawn is plentiful and the opening is brief. You have not gained a margin. You have changed the rules in favour of the first spore that enters.

A hot bath, held roughly between 65 and 75 °C for an hour or more, is the window in which people pasteurise straw at home. Below that, for a short time, too much survives. A long boil waterlogs the straw, it loses structure, and the water that remains is the film bacteria return to first. It is not “safer” because it boils. It is wetter. Cold pasteurisation with lime is another craft: it works by pH, not by heat, and it asks for doses and rinses that are not the path here. If the bag in your hand is already pasteurised, that heat has been done. Reboiling it “to be careful” does not add sterility. It adds water.

Pasteurised straw is this substrate, already through the heat, in one or two kilos. It is not sterile. You do not inoculate it with a syringe as if it were. You spawn it with colonised grain.

Substrato Funghi Paglia Pastorizzata — 1 kg / 2 kg€11,90

The spawn, and how much of it

Liquid culture is too dilute for this race. A few millilitres in a kilo of straw that still has a residual flora is a slow front in a large volume. Colonised grain is thousands of points. That is why the path is syringe into grain, grain into straw, and not syringe into straw. People who skip the grain usually get a bag that smells sour before it turns white, and blame the species.

The useful ratio often sits between one part spawn and five or ten parts straw, by weight. More spawn, the faster the white closes the volume, the shorter the window in which pasteurisation’s survivors can reorganise. Less spawn, you save grain and you lengthen the window. Below that ratio, on straw that is not sterile, you are asking a few seeds to defend a mattress. It is not a recipe for final kilos. It is a reduction of undefended time. A kilo of spawn on a kilo of straw colonises quickly and is not an elegant use of grain: it works, and it wastes bridge. A handful in an enormous bag is the opposite mistake.

You mix so the seeds do not all stay on top. You open the minimum, clean hands, clean bench, away from plants and flour. You close it. That opening is the only one this substrate justifies before fruiting, and it is done with spawn that is already white, not out of curiosity. Straw sitting open on the table while you look for the grain bag is collecting spores.

How it is packed

Proper straw, squeezed, gives a drop or two, not a stream. It is moist inside the stalks and not shining with free water. If the pasteurised bag arrives dripping, let it drain before you spawn it. Spawning into a puddle is spawning bacteria. If it arrives dry and crumbly, it is not “ready because it is clean”: mycelium does not colonise a stalk with no reserve, and adding a random glass of water creates sodden zones and dry zones. Better to recognise an out-of-range bag than to invent a hydration on the spot.

You fill without turning the block into a brick. The air in the stalks is part of the substrate. A fist that presses out all the air leaves a core that does not breathe: the oyster arrives tired or does not arrive, and the core turns sour while the outside is white. A bag full of enormous holes, straw in suspended tufts, colonises in patches and dries out. The hand should compress until the large voids are gone and stop before the block goes dull. Then you close it, with the filter clear, a label of species and date. Oyster temperature, often 18–24 °C, not on the radiator. Pink and yellow prefer the upper end of that window. A garage at 12 °C makes them look dead.

You do not open halfway through colonisation to “sort it out”. You judge from the outside. When the block is white and holding together, not before, you think about the cut. White only against the plastic, with straw-coloured straw in the middle, is a crust. Cutting it exposes the middle.

The slit, the air, the long stems

The slit is made on the side, a few centimetres, when the block is colonised. On the side, and not only on top, because the fruits form where fresh air meets a surface that is not a puddle of condensation at the bottom. You press the extra air out of the bag, gently, so the primordia are not born in a bubble of CO2. You do not open half the plastic. An enormous cut increases the surface that dries. A one-centimetre cut strangles the cluster and leaves the rest of the block breathing badly. A few centimetres, high humidity on the wound, indirect light.

Long stems and small caps are a reading of carbon dioxide, not a cosmetic flaw of “the variety”. The oyster, in still air loaded with CO2, lengthens the stem looking for an exchange and keeps the cap tight. It happens in a bag that is almost closed, in a box without gaps, in a small room with no exchange. You answer with new air, without turning the room into a draught that dries the pins. Yellow, dry pins, or brown and stalled ones, are the other extreme: wind or low humidity. Mist the air of the room, or the walls of a humid chamber, not the pins. Standing water on a primordium is a way to rot it before it is a mushroom.

A second flush is common if the block has not dried out and has not gone sour. Straw, unlike a wood block, compresses and waterlogs. A long soak turns it into a bacterial sponge. If it has become light, a bath of a few hours, then a real draining, until it no longer drips. If it smells sour after the first flush, water does not wash that out. You stop. A third harvest is possible and it is not owed.

Pink and yellow, not two coloured pearls

Pearl and blue oyster are Pleurotus ostreatus: moderate temperature, white mycelium, a certain tolerance for a slightly cool room. Pink and yellow are other species. They ask for more warmth and they show you air mistakes sooner.

Pink oyster liquid culture is Pleurotus djamor. The mycelium can be white or faintly pink. The fruits are pink and fragile, and they last less in the fridge than pearl. It colonises and fruits well in the warmth, often unhappy below 18 °C, where the pins abort and you conclude the syringe was dead. It was not. It was in a garage. You inoculate it into grain, not into straw. The straw comes after, with the spawn. The speed of pink is not permission to skip the grain: it is why, if the straw is too wet, bacteria run hard at the same temperature too.

Pleurotus djamor Cultura Liquida 10ml – Micelio Fungo Ostrica Rosa€7,83

Yellow oyster liquid culture is Pleurotus citrinopileatus. Small clusters, thin caps, a yellow that should not be read as disease. It likes warmth, not the cold of a button mushroom. In still air it becomes a coral of stems and hardly makes a cap: it is the same CO2 lesson, easier to see because the fruit is minute. High humidity, real exchange, no direct misting on the pins. This syringe goes into grain too. Ten millilitres is not a litre of spawn. It is the start of the bridge.

Indirect light is enough to orient the caps. Total darkness does not stop fruiting. It makes it paler and longer in the stem. Direct sun dries the slit and cooks a strip of mycelium. A corner of a room, without the blast of a radiator, is the place. Not a professional cellar.

Pellets are not the finished bag

Straw pellets are compressed straw, dry, raw. They have not seen the hot bath. They are not a pasteurised substrate someone has merely reduced in volume. They are rehydrated, they swell a great deal — the final volume is many times the dry pellet — and they then have to be pasteurised properly, or sterilised if that is the process you know how to close. Throwing them in water and spawning is spawning reconstituted field dust. The oyster sometimes wins anyway, and you learn the wrong lesson, until a July when it does not win any more.

Straw pellets are the ingredient, in the kilos you need so you do not stop halfway through hydration. They make sense if you are the one applying the heat, in a container that can hold the swell, up to a straw that gives a few drops when squeezed, and then the right heat, not lukewarm water for a scant hour. If you have no way to pasteurise or sterilise, the pellets stay in the paper bag. The substrate that is already pasteurised is the object that matches the gesture of spawning today. Mixing them up is how a beginner pasteurises “by eye” and calls a bag that was cold in the core bad luck.

Pellet di Paglia per Substrato Funghi — 1 kg / 2 kg / 5 kg€6,00

When you hydrate, the water goes in a little at a time. Pellets floating on a lake fall apart into an anaerobic mush. Pellets left dry in the centre of a bucket stay a core the pasteurisation does not moisten and that later, in the block, is a stone of hunger. You mix. You wait until the swelling has finished before you declare the volume. Then the heat. Then, once cool, the spawn. Never the syringe direct as a shortcut.

It is not a shiitake substrate

Shiitake is a wood fungus. It wants lignin in particles that hold a shape, a block that can make the brown crust, weeks of maturation after the white. Straw does not give it that structure. It compresses, it heads toward anaerobic conditions in the core, and the slow mycelium loses to whoever survived pasteurisation. Sometimes something grows, small and tired, and it looks like a confirmation. It is an exception that does not become a method. Lion’s mane and reishi stand on the same side: sterilised wood. Straw belongs to oysters, and to a few relatives equally aggressive.

An oyster can go on beech too. It does not have to. Straw is faster and better suited to this fungus precisely because it is airy cellulose and because pasteurisation is enough. Putting pink oyster on a wood meant for shiitake is not a grave mistake. Putting shiitake on the pink oyster’s straw is. The substrate is not a neutral container. It is half of the species.

What this guide is not

It is not a table of kilos and it is not permission to inject the syringe into the stalk. It is a shortened race: heat that lowers, spawn that occupies, a block that breathes, a small slit when the white is real. If the stems lengthen, the room is telling you. If the bag turns sour, the straw was too wet or too thinly spawned, and opening it does not correct that.