Which grain

Rye, millet, corn and brown rice are not the same taxi: seed size changes, and so does where the water stays.

Grain is not the fruiting substrate

Sterilised grain has one job. It takes a few millilitres of mycelium, or a wedge, and turns them into thousands of colonised seeds. Each white seed is then an inoculation point when you mix it into straw or wood. The fungus eats the grain as a bridge, not as the house the fruit bodies come out of. A bag of rye alone, opened and misted, can make a stunted cluster. You have used the taxi as if it were the destination, and you have exposed a very rich food to the air of the room at the moment it has nothing left to colonise but itself.

That is why the choice of seed is not a matter of taste. It is a matter of distance and water. A large seed is a longer journey to the centre, and a small seed is an enormous surface where excess water sits. The species in your syringe runs at different speeds. The same kernel can be a good bridge for an oyster and a trap for a shiitake, not because corn is “lesser”, but because the shiitake takes weeks longer, and in those weeks every water mistake works for someone else.

The bags discussed here arrive already hydrated and sterilised, with a port. You do not rinse them, soak them, or “finish the cooking”. Adding water to a sterile bag is the surest way to stop having a sterile bag. You judge what is inside, from the outside, and you either inoculate or you discard.

Where the water sits

Water activity is not how much water you put in the pot. It is how much of that water is free, available, not bound inside the seed. Many bacteria that spoil spawn want a film to swim in, an activity close to that of pure water. Mycelium, by contrast, enters the kernel. A swollen seed is enough, hydrated inside and dull on the surface, with no puddle at the bottom of the bag. That kernel is still moist enough for hyphae to grow, and dry enough outside that a bacterium has no lake.

You can see it without instruments. Shaken, the seeds move against each other. A few may have a skin just split: that is normal, especially on rye. They should not mash into a porridge if you press the bag, and they should not shine as if they were oiled. Clear condensation on the plastic, after a trip from cold to warm, is often just vapour that changed places. A milky pool at the bottom, seeds glued together, a sweet or sour smell coming through the filter: that is free water plus someone already growing in it. You do not inoculate.

The opposite case is the bag that sounds like gravel. Small, hard, dark seeds that never opened up. Mycelium can dust them white and stop, because there is no reserve inside. After a break it does not restart, or it restarts in patches. You do not fix it with a syringe of water through the port. The water does not distribute, it wets one spot, and that spot rots. You take another bag.

Rye

Rye is the usual bridge because the seed is medium sized and the hull helps the berries stay separate. You can see colonisation: a seed goes from beige to white, and a one-kilo bag is neither a brick of invisible seeds nor a handful of enormous marbles. Oysters, shiitake, lion’s mane and reishi run on it, at different speeds, on the same kind of seed. It forgives a little better than millet if a few berries split in the cook, as long as the others stay whole and the bottom is dry. It does not forgive a puddle. No seed does.

Sterilised rye, one kilo, with a port, is inoculated without opening it. Two or three millilitres in different places, not the whole syringe in one corner. On rye a single point will still colonise, because the seeds touch, but several points shorten the journey and show you sooner whether the liquid was alive. Then you leave it alone. The white has to enter the seed, not merely veil it.

Segale Bio 1kg/2kg Sterilizzata Autoclave • Spawn Funghi Pleurotus Shiitake€11,90

If the rye in the bag is already a single block before inoculation, someone cooked it too long or the water redistributed into a corner during shipping. A block that crumbles when you massage it from the outside can still be good. A sticky block that clumps back together like dough is not. The port does not turn dough into seeds.

Millet

Millet is small. After you break and mix, every white seed becomes an inoculum among seeds that are still bare, and the bare seeds are very numerous. Colonisation looks fast even when the mycelium, in millimetres per day, is no quicker than on rye. It is geometry. You have shortened the average distance between a colonised point and the next raw seed. For oysters this is a clear advantage. For mixing spawn into a substrate such as CVG it is another: small seeds disappear into the volume instead of staying as lumps that dry on the surface.

The price is water. The surface, for the same weight, is much higher than rye. Excess water does not sit “a little at the bottom”. It sits as a film on thousands of seeds, and that film is exactly the bacterial film. Millet forgives a long cook less, and forgives less a bag that took on condensation and held it between the seeds. If after a shake the seeds stay in damp little balls, it is not “still a bit sticky, it will pass”. It is free water spread out, which is worse than a single puddle, because you do not see it in one place.

Sterilised millet is inoculated with the same port and the same hygiene as rye, with one extra caution. The liquid in the syringe is water. Emptying all of it into a single hole, in millet that is already at the limit, creates a local wet spot where bacteria, if even one survived, start before the mycelium. A few millilitres, moved around, and then you do not touch it. Shiitake on millet works if the bag is dry in the right sense. If it is wet, the shiitake loses the race because it is slow, not because millet is forbidden to it.

Miglio Bio Sterilizzato 1kg/2kg • Porta Iniezione SHIP • Substrato Funghi€12,10

Millet packs down. A very full bag, left still, can have a core with little air. Mycelium arrives there tired, or does not arrive, and the core turns sour while the outside is white. The break, done from the outside when part of the bag is colonised, opens that core. It does not stand in for a bag that was sodden from day one.

Corn

Corn is the opposite extreme. The seed is large, the inner starch is a store, and the inoculation points per kilo are few. Mycelium whitens the surface long before it has finished the endosperm. A kernel white on the outside can still be raw inside. If you use it at that point to seed straw or wood, you are moving uncolonised starch into the substrate, and naked starch is food for whoever was waiting. That is why corn asks for optical patience: the seed should be white even where a split lets you see in, and the bag should be white evenly, not in superficial patches.

If the kernels burst, the starch comes out and glues them. Glue is kin to a puddle. The seeds no longer move, air does not circulate, the heart of the clump heads toward bacteria even if the outside smells of mushroom. Proper corn breaks into kernels, not into paste. Oysters manage it because they are fast and aggressive: they cover the surface and then go in. Shiitake on corn is a long wait, and during the wait any survivor of the sterilisation cycle has time. It is not impossible. It is a choice in which the calendar works against you.

Sterilised corn makes sense when you want seeds that stay discrete and do not turn into damp flour, and when you accept that colonisation is judged kernel by kernel. Inject in several places. On a large seed, a single hole leaves long distances, and the liquid can settle in a pocket among a few kernels. The break, at about a third white, matters more than on millet, because the still-bare seeds are far from the seeds already taken. Do not break a corn bag that shows a slimy pocket. You would distribute it.

Spawn Mais Bio 1kg/2kg Sterilizzato • Porta SHIP€11,90

Brown rice

Brown rice sits, in size, between millet and corn. The bran is fibre and a little oil. It is also why this seed glues itself the moment the cook goes past the mark: starch comes out, the kernels become a brick, and the brick has no air in the middle. If the kernels in the bag are whole, swollen and separate, rice works, especially for oysters. If they are already a shiny block, do not inoculate hoping the mycelium will “sort out” the inside. It will colonise the crust and the inside will go sour.

Sterilised brown rice is not a lesser grain when the water is right. It is a grain with a narrower cooking window, and with a slightly shorter keeping time than rye, because the oils in the bran age. A bag that smells of rancid nut, before you have even inoculated, has passed that time. It is not green-mould contamination. It is tired food, and mycelium runs poorly on it. For shiitake it is not the starting choice. The slowness of the fungus and the tendency of rice to pack together add up. For an oyster, on kernels that move, it is an honest bridge.

The port is used as on the others. Little liquid, more than one point, no opening. Rice that settled into a damp corner during the journey can be massaged from the outside before inoculation, while it is still cold and sterile, only if the kernels separate. If the massage squeezes liquid out, stop. What comes out between your fingers through the plastic is the signal that there is no dry interior left to save.

Who runs on what

Oysters, Pleurotus ostreatus and king oyster too, do well on rye and on millet. Corn is fine if you wait for the heart of the kernel. Rice is fine if the kernels are whole. Pink and yellow are warmer, faster oysters: they prefer seeds that do not hold a film of water, because at the temperature where they run, bacteria run too. Sodden millet in a room at 25 °C is a race the fungus often does not win, even if the species is “easy”.

Shiitake wants rye as a habit. Millet is acceptable if it is dry in the sense described above. Corn lengthens a calendar that is already long. Brown rice is the one I would avoid as a base, not because of a species ban, but because of the glue. Lion’s mane follows the same logic as rye and millet, and it tolerates grain that has gone sour badly: it stops at a line and does not cross it. Ganoderma species are slow. The choice of seed weighs less than cleanliness, and rye remains the bridge that lets you see the white without forcing you to guess the inside of a corn kernel. Agaricus, button and almond, will use this spawn inside CVG, not as a fruiting substrate. There millet mixes more evenly. Rye works. Corn leaves large seeds that surface and dry out, and a dry seed on the surface is a point where a mould lands after you have opened the bag.

None of these preferences is a medal. A bag of millet with free water is worse than a bag of rice with the kernels right. The species does not read the label. It reads water and distance.

What you see when the water is wrong

Too much free water: shiny seeds, clumps, a sweet, sharp or rotten-apple smell, mycelium that stops at a yellowish border, sometimes a slimy patch that spreads even though you have opened nothing. The English name for that patch is wet spot. In practice it is a bacterium that found the film. You do not cut it out. It is in the whole bag the moment you see it expanding, and breaking the bag spreads it.

Too dry: powdery white that does not hold, seeds that stay their original colour under a dusting, no restart after the break, a faint smell or a smell of dust instead of fresh mushroom. This does not get wetted afterwards either. You recognise it early, so you do not build a straw substrate on top of it convinced you have sown something.

A denser sector, while it stays white and smells clean, is not wrong water. It is mycelium that found a group of seeds and took them before the others. You break and mix from the outside, when you are around a third, precisely so that sector is not the only one. How that break is done, and when instead it spreads a problem, is another guide. The decision here comes earlier: which seed you are holding, and whether the water in that bag is still a hydrated interior or is already a puddle.

What this guide is not

It is not a quality ranking and it is not a promise of kilos. It is why four sterilised seeds, all of them “grain”, behave as four media. If the bag you have is glue, no name on the packet turns it into spawn.