A Night in an Underground Mushroom Farm

Transcript

Chapter 1: The Door Beneath the Hill

Night has settled over the quiet road beside the hill.

The air is still warm from the day. Grass along the verge holds a little of the evening’s heat, and small insects move among the stems. Their faint calls rise and fall beneath the soft rustling of leaves. Beyond the road, the hill appears as a long, dark curve against the sky.

There is little to suggest that people are working beneath it.

A short paved path leads away from the roadside. Low lamps mark its edges, casting warm circles across the ground. At the end stands a modest metal door set into a wall of pale stone. A clear sign gives the farm’s name and the number of the entrance. Beside it are a covered notice board, a small light, and an access panel for authorized staff.

The entrance is practical rather than mysterious. The path is level. The hinges are maintained. Emergency lights and marked routes wait beyond the threshold. This was once an industrial quarry, and it remains a working place, shaped by careful planning, regular inspection, and familiar routines.

When the outer door opens, a ribbon of cool air passes across the path.

It carries a mild mineral scent, something like rain falling on stone. Farther inside, a ventilation fan produces a low, even hum. Shielded work lights reveal pale limestone walls and a clean passage descending at a gentle slope.

This hill contains a renovated limestone quarry. Many years ago, stone was cut from beneath the ground and carried away for building. The old workings left broad corridors and chambers. Much later, some of those spaces were adapted for cultivating mushrooms.

The primary crop here is the white button mushroom, known scientifically as *Agaricus bisporus*. It is a familiar mushroom, usually harvested while the pale cap is still rounded and closed.

White button mushrooms have historical links to underground cultivation. In France, commercial growers adapted abandoned limestone quarries near Paris. Similar systems later appeared in other quarries and cellars. These underground places offered shelter from the sharp changes in weather taking place above them.

The limestone surrounding this farm has what engineers call thermal inertia. In simple terms, the rock changes temperature slowly. A summer afternoon may heat the road and the grassy slope while the deeper quarry remains cool. During cold weather, the underground stone also loses heat more gradually than an exposed structure might.

Deep underground areas may remain close to a region’s mean annual temperature. But this is only a general pattern. Conditions vary with depth, airflow, the number of openings, and the shape of the tunnels. A chamber near a broad entrance may respond fairly quickly to the weather, while a room farther inside the hill may remain much steadier.

The quarry also tends to retain moisture. Naturally high humidity can help keep growing beds from drying too quickly. Yet moisture is not helpful in every form. Condensation may gather on ceilings, pipes, or walls, creating sanitation concerns. Water must be guided into drains, removed where necessary, and kept away from places where it does not belong.

For that reason, the quarry itself is only the outer shell of the farm.

Within the old stone passages are constructed growing rooms with insulated doors, washable surfaces, drainage channels, water lines, electrical systems, sensors, and ventilation ducts. Reliable lighting marks each working route. Fresh air can be brought in, used air can be carried away, and the conditions in separate crop rooms can be managed according to their stage of production.

The hill provides a steady background. Modern equipment and skilled attention create the precise growing environment.

Most mushroom farms are not underground. Purpose-built mushroom houses on the surface are more common, and they can control temperature, humidity, and airflow just as carefully. An old quarry becomes useful only when it can be made safe, clean, accessible, and efficient. Its natural stability may reduce some climate-control demands, but it does not replace thoughtful design or daily work.

Nor are mushrooms cultivated here simply because they love darkness.

Mushrooms are fungi, not plants, and they do not use sunlight to make food through photosynthesis. Even so, darkness alone does not produce a crop. Light requirements vary among cultivated species. For white button mushrooms, success depends more on prepared compost, suitable moisture, controlled temperature, fresh air, cleanliness, and careful timing.

The first stages of compost preparation do not take place in these underground rooms. Raw composting generates heat and requires space, air management, and specialized equipment. At this farm, that work is carried out at a separate surface facility. The quarry receives compost after it has been prepared for the later stages of production.

Tonight, several batches are already in place. In the rooms ahead, mushrooms are growing at different points in their cycle. Some remain hidden, with their fungal growth spreading through the compost. Others have begun to form small white caps. Farther along the route, a mature crop is ready to be gathered by hand.

The overnight shift will inspect the growing rooms, record environmental readings, harvest selected beds, and pack orders for the morning. The mushrooms do not require people to work at night. The schedule is a practical choice. It allows fresh harvests to be monitored, packed, cooled, and prepared before early deliveries leave for shops, restaurants, and markets.

For now, the journey has reached only the threshold.

A little surface warmth still lingers near the entrance. Behind us are the insects, the grass, and the quiet road beneath the night sky. Ahead, pale limestone catches the shielded work lights. The distant fan continues its steady rhythm, carrying air through rooms that cannot yet be seen.

The outer door closes softly.

The sounds of the hillside grow faint. The rustling leaves and evening insects recede until they are little more than a memory.

Several steps farther on, a second, cleaner doorway waits beneath an illuminated sign. It marks the boundary between the old quarry passage and the controlled interior of the farm. Beyond it, outdoor shoes, drifting air, and the changing weather must be left behind.

The cool passage continues beneath the hill, and the quiet overnight route begins.

Chapter 2: Leaving the Surface Behind

The illuminated sign above the second doorway reads, “Hygiene Entrance.” Beside it, a smaller notice lists the simple steps required before anyone passes into the clean growing areas.

The first door opens into a bright vestibule. It is not quite an air lock, because the space is not designed to maintain a controlled difference in air pressure. It is simply a double-door entry, arranged so that one door closes before the next one opens. This helps separate the working farm from the quarry entrance, and from the outdoor world beyond it.

The door seal releases with a quiet sigh.

Inside, the walls are smooth and pale. A sanitation mat lies across the floor. Beyond it is a boot-cleaning station, with shallow brushes and a low metal rail. There is a handwashing sink, a soap dispenser, and a neat row of hooks holding clean outer coats. Hair coverings and disposable gloves wait in covered boxes nearby.

These precautions are ordinary parts of food production. They do not suggest that the mushrooms are dangerous, or that the people working here need protection from them. Clean clothing and footwear simply reduce the amount of dust, soil, spores, and other material carried from one part of the farm to another.

The soles of our boots pass slowly over the brushes. Water moves between the bristles, then disappears into a narrow channel. Hands are washed and dried. A clean coat is fastened over the clothes worn outside.

By now, the jacket that felt comfortable on the hillside has become slightly too warm. The underground air is cooler than a summer afternoon, yet warmer and more settled than the night air near the entrance. The quarry stone changes temperature slowly. It softens the sharp differences between day and night, and between one season and the next.

A radio is taken from its charging rack and clipped into place. Its indicator gives a small green blink. Staff members use radios to remain in contact across the farm, keeping communication simple as they move between separated rooms and working zones.

The inner door opens only after the first has closed. Another quiet sigh comes from the rubber seals. Then we step into the main corridor.

Footsteps sound different here. On the clean concrete, each step becomes rounded and low, returning from the stone in a gentle echo. The corridor is wide enough for workers and small wheeled carts to pass comfortably. Overhead, electrical cables and pipes travel in straight, carefully supported lines.

The original quarry walls remain visible in places. Between them, insulated panels and constructed partitions divide the underground space into separate rooms. Heavy doors mark the growing chambers. Flexible curtains hang across a few service openings where carts pass regularly.

This separation serves a practical purpose. Compost handling takes place in one zone. Growing happens in another. Harvested mushrooms follow a clear route toward the cooling and packing areas. By reducing unnecessary movement between these places, the farm also reduces the movement of insects, dust, and unwanted microorganisms.

A working farm cannot be separated completely from the living world around it. Instead, the staff rely on sensible boundaries and steady routines. Tools remain within their assigned zones when possible. Boots are cleaned. Surfaces are washed. Workers follow marked routes rather than moving back and forth without reason.

A blue line painted on the floor leads toward the growing rooms. A green line turns toward packing. At every junction, clear signs repeat the room numbers and point toward the nearest maintained exit. Emergency lights sit above the doors, ready to illuminate the route if the ordinary lamps should fail.

The numbered rooms make the old quarry feel measured and understandable. They are reassuring landmarks beneath the hill, not the branches of a maze.

Room 1 is a service room. Rooms 2 and 3 hold crops at early stages. Farther along, Room 7 is scheduled for harvesting before dawn. At each doorway, a small card identifies the batch inside and records the dates of its cultivation cycle.

Low amber and white lights appear at measured intervals. They are bright enough for safe work, yet gentle against the pale limestone.

Button mushrooms do not need sunlight in the way green plants do. Plants use light for photosynthesis, the process by which they make sugars from carbon dioxide and water. Fungi belong to a different branch of life. They obtain energy by absorbing nutrients from the material in which they grow.

For that reason, a mushroom farm can operate deep beneath a hill. Complete darkness, however, is not the secret of cultivation. Darkness may be convenient, and an underground setting offers protection from the changes of weather above, but cleanliness and environmental control matter more.

The workers still need clear and dependable light. They need it to inspect the crop, read labels, clean the rooms, guide carts, and move safely along the corridors. Here, the lamps provide what is required without making the underground passages feel harsh or bright.

We continue down a gentle slope. A stainless-steel handrail runs beside the wall. When touched, it feels cool. A fine line of condensation has gathered along its lower edge.

A passing worker wipes the moisture away, then pauses to check the floor.

The concrete slopes almost too slightly to notice. Water used for washing, along with droplets that gather from the humid air, is guided toward narrow drains along the sides of the corridor. It is better for water to enter a managed drainage system than to remain standing on the floor. The drains are covered by metal grates and kept clear as part of the regular cleaning routine.

Another pair of workers approaches with an empty cart. Their coats match the color assigned to the growing zone. They offer quiet greetings and continue toward the harvest rooms. The wheels make a soft, even sound over the smooth floor, fading slowly after the cart has passed.

Behind us, the hygiene vestibule is now out of sight. The outdoor night feels much farther away, although the distance traveled is not great.

What has changed most is the quality of the air. It no longer carries the scent of grass, warm soil, or the quiet road. Here there is cool stone, clean water, and the mild earthy trace of prepared compost behind closed doors.

The air is still, but not motionless. Somewhere beyond the constructed walls, ventilation fans continue their steady work. Their sound is softened by distance until it becomes a low and constant breath.

The blue line carries us onward. We pass another emergency sign, another numbered door, and another pool of gentle amber light. The arrangement is simple and deliberate. Clean routes lead toward clean rooms. Harvest routes lead toward cooling and packing. Each doorway marks a boundary, and each boundary helps the night’s work remain orderly.

At the next junction, the blue floor line ends beside a small wall display. Soft digits glow beneath a clear cover. They show the temperature, humidity, and condition of the air in the rooms ahead.

For a moment, the numbers appear perfectly still.

Then one changes by only a fraction.

That small movement reveals how carefully the farm is managed. The underground climate is not left to chance. It is watched continuously, recorded carefully, and adjusted with patience.

Chapter 3: The Climate of the Tunnels

The wall display glows at the junction, its pale digits reflected faintly on the polished floor. One number marks the air temperature. Another shows relative humidity, the amount of moisture in the air compared with the maximum it could hold at that temperature. A third records the concentration of carbon dioxide.

Beside the display, a small green light remains steady.

A worker pauses to read the figures. Her name is Mara, and part of her night shift is spent following these quiet measurements from room to room. She does not need to make an adjustment here. She simply enters the readings into a handheld device, listens for a moment, and continues along the corridor.

Above us, hidden beyond metal panels, air moves through broad ducts. The sound is low and even. Every so often, a relay clicks. The note of a fan changes slightly as its motor slows or gathers speed. Then the sound settles once more into the background.

The tunnels provide a naturally sheltered setting, but they do not create a perfect mushroom climate by themselves. Stone can soften the changes between day and night. The underground rooms are protected from wind, direct sun, frost, and summer heat. Even so, the crop creates changes of its own.

Button mushrooms grow in prepared compost. Within that compost, fungal mycelium is active, and so are communities of microorganisms. As they use nutrients, they release heat. The compost and the developing crop also respire, using oxygen and releasing carbon dioxide.

In a long room filled with growing beds, all that quiet activity adds up.

Mara opens a viewing panel without entering the room. Beyond the glass are parallel shelves. Each one holds a deep layer of compost beneath a casing layer. Everything appears still, but the sensors tell a more detailed story.

A probe placed within the compost measures warmth where biological activity is strongest. Other sensors measure the surrounding air. Together, they help the growers understand what is happening throughout the room, even when little seems to be changing.

During the spawn run, when mycelium is spreading through the compost, an illustrative compost-temperature target might be about 75 to 77 degrees Fahrenheit, or 24 to 25 degrees Celsius. Relative humidity is often kept around 90 percent or higher, so exposed surfaces do not dry excessively. At this stage, growers may allow more carbon dioxide to remain in the room, because higher levels can support vegetative mycelial growth.

These figures are examples, not a universal recipe. Each farm adjusts its settings according to the mushroom strain, the compost, the room design, the equipment, and the precise age of the crop. Conditions suitable for one stage may no longer be suitable a few days later.

Mara touches the display and brings up a simple graph. The lines rise and fall gently across the hours. There are no perfectly straight lines in a living growing room. Heat gathers. Moisture shifts. Fresh air enters. The control system responds in small, measured steps.

Farther along the service passage, a ventilation cabinet stands behind a closed door. Through it comes the muted rush of moving air. Fans distribute temperature and humidity through the growing rooms, preventing stagnant pockets from forming around the beds and shelves. They also help remove excess carbon dioxide and bring in carefully measured fresh air from outside.

Without circulation, one corner might become warmer than another. Moisture could gather unevenly. Carbon dioxide could remain around the crop, even if the reading near the doorway appeared acceptable. The aim is not simply to create the correct average. It is to keep conditions reasonably even throughout the room.

At the next panel, the humidity reading is high, yet the corridor remains clear. High humidity does not mean visible fog must always hang in the air. Moisture can be carefully managed without turning each room into a cloud. Fine droplets may sometimes appear near humidification equipment, and beads of water shine along a pipe. Most of the moisture, however, remains invisible as water vapor.

Any water that condenses must still have somewhere to go. The floors slope almost imperceptibly toward narrow drains. Mara shines a light through a grated cover and checks that the water is moving freely.

Drain conditions are recorded along with water use, fan speed, airflow, air temperature, compost temperature, relative humidity, and carbon-dioxide concentration. Each reading describes one part of the underground climate. Together, they form a patient record of the room through the night.

Carbon dioxide requires particular care because it is odorless. A person cannot reliably smell when its concentration is elevated. Some stages of mushroom cultivation can use carbon-dioxide levels above occupational exposure limits for an eight-hour workday. For that reason, workers do not depend on their senses, and they do not enter every room whenever they wish.

Sensors monitor the air continuously. Ventilation lowers concentrations when necessary. Access may be restricted, and safe air conditions are confirmed before workers enter certain rooms. These are ordinary safeguards in a well-managed farm, as routine as clean clothing, washed tools, and carefully marked doors.

Mara stops beside a sealed cropping room. The air inside is cooler than the air in the incubation area. During fruiting and cropping, button mushrooms are often kept at air temperatures somewhere around 57 to 66 degrees Fahrenheit, or 14 to 19 degrees Celsius. The exact setting depends on the strain, the stage of growth, and the farm’s methods.

The transition into fruiting is made gradually. More fresh-air exchange lowers the carbon-dioxide concentration. Temperature and humidity are adjusted as well. In some systems, pinning, the formation of the first tiny mushrooms, may be initiated around or below roughly 800 to 1,000 parts per million of carbon dioxide. Other growers use different targets. Their decisions depend on the crop, the equipment, and long experience with the rooms.

A fan changes speed behind the wall. Its sound deepens for a few moments, then settles into a softer rhythm. On the display, an airflow symbol turns slowly. Mara watches until the reading steadies.

Nothing here is held forever at one setting. The climate changes with the crop. Incubating mycelium needs one balance. Pinning mushrooms need another. Mature mushrooms, nearly ready for harvest, require another pattern of cool air, moisture, and ventilation.

The machinery does not force growth. It creates a suitable space in which growth can proceed.

We follow the corridor past pipes labeled for fresh air and return air. A thin line of water travels toward a drain, catching the dim light before disappearing beneath the grate. Behind sealed doors, compost releases warmth, mycelium spreads, and fans carry away what is no longer needed.

The readings on the wall tell only part of the story. To understand what the fans are protecting, and what the sensors are measuring, we turn into a service corridor leading toward the receiving area.

There, prepared compost arrives from aboveground, carrying the materials from which the next crop will quietly begin.

Chapter 4: Preparing the Growing Medium

The service corridor widens as we approach the receiving area. Here, sturdy rails line the walls, and the floor slopes gently toward narrow drains. A loading door connects this underground passage to a covered bay nearer the surface. Through that door comes the prepared compost for the farm’s main crop: white button mushrooms.

A low cart waits beside a row of empty trays. Its load is dark brown and loosely piled, with pale lengths of straw still visible. Beneath the muted lamps, the compost looks soft but substantial. It can hold moisture, while leaving small spaces through which air can move.

Mara takes a sample in one gloved hand.

She presses it gently between her fingers. The material holds together for a moment. Then, as she opens her hand, it crumbles back into place. A few straw fibers lie across her palm. The scent is earthy and muted, without the sharpness that unfinished compost might carry.

“This is ready,” she says quietly.

White button mushrooms do not grow in ordinary garden soil. Their growing medium is a specially prepared compost, designed to provide the moisture, structure, and nutrients that mushroom mycelium needs. Here, the word substrate simply means the material in which the fungus will grow, and from which it will gather nourishment.

The exact compost recipe can differ from one producer to another. It may contain straw, horse-stable bedding, poultry material, corn cobs, hay, gypsum, and other agricultural by-products. These ingredients are not discarded materials thrown together at random. Each becomes part of a carefully managed mixture.

Horse manure is often associated with traditional mushroom production, but it is not essential to every recipe. Some composts include it. Others rely on different combinations of straw and agricultural materials. Button-mushroom compost is not simply rotted manure. It is a deliberately prepared, biologically active, selective growing medium.

Most of that preparation takes place far from these underground rooms.

During the first stage, called Phase One composting, the raw ingredients are blended with water and exposed to oxygen. Microorganisms already present in the materials begin to use the mixture as food. Their activity produces heat naturally, warming the compost from within.

The mixture is turned repeatedly. Turning redistributes moisture, brings in oxygen, and helps the materials change more evenly. This work requires open space, turning equipment, good ventilation, and careful management of water draining from the compost. For those reasons, Phase One is usually performed aboveground rather than deep inside a quarry.

This farm receives compost that has already passed through that first stage. Trucks arrive on a planned schedule, carrying material prepared at a specialized surface facility. By the time the compost reaches the receiving bay, its coarse ingredients have softened and blended, although individual strands of straw can still be seen.

But Phase One is only part of the process.

The compost must also pass through Phase Two, which has two broad purposes. The first is pasteurization. Controlled heat reduces pests and undesirable organisms that might interfere with the mushroom crop. In a traditional treatment, the compost may be held near 140 degrees Fahrenheit, or about 60 degrees Celsius, for several hours. The precise temperature and timing vary with the system and the condition of the compost.

Pasteurization is not the same as sterilization. Sterilization attempts to remove nearly all living organisms. Pasteurization is gentler and more selective. It reduces troublesome organisms while allowing a useful microbial community to remain.

The second purpose of Phase Two is conditioning. As the compost develops, nitrogen-containing materials can release ammonia. Free ammonia can damage mushroom mycelium, so the compost must be conditioned until the ammonia has been removed or converted into less harmful forms.

This is one reason Mara pays attention to scent. Finished compost should no longer carry a strong ammonia odor. Instruments and production records provide more exact information, but an experienced worker also learns the familiar qualities of a good batch: its color, texture, moisture, springiness, and mild earthy smell.

Mara lets the sample fall into a shallow testing container. Then she checks the label attached to the cart. The record lists the batch number, preparation date, supplier, and delivery time. Every tray filled tonight will remain connected to that information as it moves through the farm.

Nearby, a mechanical loader begins to tip compost into an empty tray. Its movement is slow and measured. The dark material spreads from one end to the other. A leveling bar passes above it, leaving a smooth, even surface. Loose strands of straw settle across the top.

When the tray is full, a worker checks its depth along both sides. The compost must be distributed evenly. An uneven bed can retain moisture differently from one place to another. It may also release heat unevenly as the crop develops.

The worker makes a small adjustment near one corner, drawing a little compost across a shallow space. Then the tray rolls forward and settles onto the metal rails with a low, rounded sound.

Soon it will join the other trays in the production rooms, arranged in long beds beneath the ventilation ducts. There, the cool air, measured humidity, and steady circulation will support the next stages of the crop.

Not every cultivated mushroom uses this kind of growing medium. Oyster mushrooms are often raised on pasteurized straw, or on sawdust-based material that may be sterilized before use. Shiitake mushrooms are often grown on hardwood logs, following a slower traditional method, or on supplemented blocks made largely from hardwood sawdust.

Each species has its own relationship with its substrate. The material, preparation, moisture, and treatment must suit the fungus being cultivated. Here, however, the underground rooms are arranged mainly for white button mushrooms and their compost-filled beds.

Another empty tray moves beneath the loader. Compost falls softly into it. The leveling bar passes over the surface. A worker checks the depth, reads the label, and guides the tray onward.

Then another tray takes its place.

The work repeats with little variation. Dark compost falls. Straw fibers settle. Wheels move along rails. The sounds blend with the distant ventilation fans and the faint movement of water toward the drains.

Nothing in the receiving area appears hurried. Yet every careful step supports all that will follow. The compost has been blended, warmed, turned, pasteurized, and conditioned. It has traveled from the surface facility into the shelter of the quarry. Now it rests in an even layer, holding moisture, air, and nourishment within its springy structure.

Inside each tray, the prepared compost is ready, but still quiet.

Its next visitor is almost invisible at first: grain carrying the living threads of the mushroom fungus.

Chapter 5: The Hidden Work of Mycelium

The grain arrives as small, clean kernels scattered through the prepared compost. Rye, wheat, millet, and sorghum can all be used for this purpose. Each grain carries a selected culture of the button mushroom fungus, grown under carefully controlled conditions by a specialist producer.

This material is called spawn.

Spawn is sometimes compared with seed because it serves as a starter for a new crop. Yet it is not truly a seed. Mushrooms are fungi, not plants, and their growth is different from the growth of a plant.

Most commercial growers do not begin each crop directly from spores. Instead, they buy spawn from specialist producers. These producers maintain selected fungal cultures and allow them to spread through sterilized cereal grain. The prepared grain gives the chosen fungus a clean material to colonize.

Once the grain is ready, it is sent to farms like this one. Here, the spawn is mixed evenly into the compost. The separate grains become many small starting points from which the fungus can continue to grow.

At first, little seems to be happening.

The surface of a newly filled tray remains dark and uneven. Pieces of straw lie across one another. Moist compost settles into the spaces between them. A label at the end of the bed records the batch and the date when the spawn was added. Above it, the ventilation system maintains a steady movement of conditioned air.

Within the compost, however, the fungus is extending microscopic filaments called hyphae.

A single hypha is much too fine to study from the walkway. It grows by lengthening at its tip and may branch repeatedly as it passes through suitable material. Many connected hyphae together form a larger network called mycelium.

Mycelium is the main feeding body of the fungus. The familiar mushroom is only a temporary reproductive structure, known as a fruiting body. It appears for a limited time above the compost, while the mycelium remains within the material below.

This distinction is easy to miss when mushrooms are seen in a field, a forest, or a market basket. The cap and stem are the visible parts, so they seem to be the whole organism. Here in the growing bed, the larger pattern becomes clearer. Long before any rounded caps appear, the fungus is already present, spreading quietly through the compost.

Hyphae are sometimes loosely compared with roots, but they are not roots. Plant roots are specialized structures with their own biology. Fungal hyphae are different. They release substances that help make useful material available around them. The fungus then absorbs dissolved nutrients through the surfaces of these fine filaments.

As the mycelial network develops, it takes resources from the substrate and transports water and dissolved nutrients through the colonized compost. When button mushrooms later rise above the bed, they will remain joined to this network. They will not be separate plants rooted in the tray. They will be fruiting bodies produced by the fungus already living throughout the compost.

This period of spreading growth is called the spawn run.

During the spawn run, mycelium extends outward from each colonized grain. Fine white threads may begin to appear between pieces of straw. Around some grains, the growth forms denser, pale patches. Elsewhere, it remains hidden deeper in the bed.

Its appearance is not identical throughout the compost. Depth, moisture, and the nature of the substrate can all affect what is visible. A patch near the surface may look soft and pale. Growth beneath it may be more extensive, yet completely concealed by the dark compost. Growers therefore do not judge the progress of a crop from one visible patch alone.

The quiet surface offers clues, but only clues.

A worker pauses beside one of the trays and lifts a long temperature probe. With a smooth movement, she guides it down into the compost. The narrow metal stem disappears almost to its handle.

Then she waits.

There is no need to rush the reading. The low sound of the ventilation fans continues beyond the wall. A bead of water gathers along a nearby pipe. The worker keeps one hand on the probe while the display slowly settles.

The compost has its own temperature, which may differ from the air in the room. Active colonization can generate significant heat as the fungus uses the resources around it. In a large bed, that heat matters. Growers monitor the compost temperature as well as the room air, because the reading inside the tray reveals what the mycelium itself is experiencing.

The display becomes steady. The worker reads the number and enters it on a tablet. Then she withdraws the probe without hurry. Before moving to the next batch, she cleans the instrument according to the farm’s routine.

The reading joins other measurements gathered through the night. One number cannot tell the entire story. A series of records can show whether conditions have remained steady and whether the spawn run is progressing as expected.

Across the beds, thousands of grains serve as starting points for many expanding patches. The hyphae continue to lengthen and branch. Gradually, neighboring areas meet, and the compost becomes more completely colonized.

Even so, the entire farm should not be imagined as one enormous individual fungus. Separate trays and batches have their own introduced cultures and their own boundaries. Nor is the mycelium an underground mind. Its activity follows ordinary biological processes. The hyphae extend, branch, absorb nutrients, transport water and dissolved materials, and respond to the conditions around them.

The result is quiet but substantial. Prepared compost gradually becomes colonized compost, filled with fungal tissue too fine to distinguish at a casual glance. From the far end of the room, the beds may appear almost unchanged. Only a few pale threads near the surface suggest the work continuing below.

For now, no round caps rise from the trays. There are no stems to cut or twist free, and no neat containers waiting in the packing room. This stage is devoted to establishing the fungal network that will later produce the visible crop.

The worker moves to the next tray. Again, the long probe enters the compost. Again, she waits for the reading to settle.

Around her, the underground farm continues at its measured pace. Air moves through the ducts. Moisture rests within the beds. Fine white hyphae spread between pieces of straw, sometimes visible and sometimes hidden.

As the network continues its unseen work, the farm’s growing rooms begin to take on rhythms of their own. Some trays are newly colonized. Others are farther along. All are arranged in calm succession through the underground halls.

Chapter 6: Rooms of Patient Growth

Beyond the incubation room, the underground hall divides into a series of orderly passages. Each doorway carries a simple sign. There is a room number, a batch code, and a date. The markings are plain, yet together they describe the rhythm of the farm.

One room has recently received colonized compost. Another holds beds covered with casing. Farther along, a room is being prepared for the first mushrooms to form.

The stages are kept separate. A single growing room does not normally contain every part of the cycle at once. Instead, each room holds a batch at roughly the same stage. This makes the conditions easier to manage and allows the workers to follow a predictable schedule.

While one batch continues to develop, another may soon be ready for harvest. Somewhere else, an empty room can be cleaned and prepared for the next crop. In this way, the farm produces mushrooms week after week, rather than waiting for one great harvest from every room at the same time.

A worker opens the next insulated door. Soft work lights come on inside.

Long shelves extend toward the far wall. They are stacked in several levels, one above another, with straight aisles between them. Each level supports a shallow bed or tray of compost. The shelving multiplies the useful growing area without increasing the footprint of the room. Where one bed might have occupied the floor, several now rise through the cool air in parallel layers.

Button mushrooms can be cultivated in several kinds of production units. Some farms use long, Dutch-style shelf beds. Others use large trays, bags, or systems designed for their particular buildings and equipment. Here, the central growing rooms use stacked beds and trays fitted neatly into the former underground chambers.

Despite the number of shelves, the room feels spacious and measured. The aisles are clear. Signs identify each section. Pipes, cables, and sensors follow deliberate routes along the walls and ceiling. The predictable rows make the chamber easy to understand. Nothing needs to be hurried.

A narrow cart rolls into the room. One wheel passes over the joints in the smooth floor with a quiet, repeating sound.

A soft bump.

Then another.

The worker stops beside the first stack and checks the code on a tablet. Its screen shows the history of the batch. It notes when the compost arrived, when it was spawned, and how long the mycelium was given to spread. It also holds readings gathered from the room.

These records allow one shift to continue the observations of the last. A clipboard could serve the same purpose. What matters is that each small change is noted, and that the crop can be followed from one stage to the next.

The depth of the compost is carefully controlled. It is not simply piled as deeply as the beds will hold. During active colonization, biological activity produces heat. If the compost is too deep, that heat can collect within it and become difficult to manage. A consistent depth helps the air system and the growers maintain suitable conditions throughout the bed.

Above the darker compost lies a lighter layer called casing.

The casing is not another rich source of food like the prepared compost beneath it. Its main role is to hold moisture and create a suitable surface environment for mushroom formation. Depending on the stage of the batch, a bed may be waiting to receive this layer, or the casing may already have been spread evenly across it.

In this room, the surface is pale brown and gently textured, like fine, damp earth beneath the subdued lights.

The worker does not press a hand into it. Unnecessary touching is avoided. Instead, the casing is studied carefully from the aisle.

Its texture offers useful clues. A patch that appears too dry may need attention. A surface that remains too wet can also create difficulty. The aim is not saturation. It is a steady balance, maintained through small observations and measured adjustments.

A nearby sensor provides another reading. The worker waits for the number to settle, records it on the tablet, and moves a few steps farther along the row. There, the casing is examined again.

Observe.

Record.

Move on.

The repeated actions are quiet enough to blend with the low sound of ventilation. Most of the crop remains undisturbed. The workers look closely, but they touch only when there is a reason.

Although the room is humid, the beds are not constantly soaked. Much of the crop’s moisture is managed through careful irrigation of the casing and through control of humidity in the surrounding air. Water is applied according to the stage of growth and the condition of the surface. It is not sprayed without purpose over every visible part of the room.

Later, when mushroom caps have appeared, persistent water resting on them will be undesirable. Button mushrooms are delicate, and caps that remain wet for too long can lose quality. Humid air is useful, but a continuously wet surface is not the goal.

The floor is also designed to drain and remain clear. Standing water in the aisles would interfere with cleanliness and make the room harder to manage.

Near one metal support, a few beads of water have gathered. They catch the low light without falling. Below them, the floor remains dry.

The worker looks upward, checking that the moisture has not become excessive, then continues along the row. No adjustment is needed.

Many good observations end this way. A condition is examined, found to be within its intended range, and left alone. Care sometimes means making a change. Just as often, it means recognizing that no change is necessary.

At the next doorway, another sign shows a different batch code and date. Inside, the shelves look much the same, but the crop is several days farther along. Fine traces of mycelium have begun to rise toward the casing surface. They appear in scattered pale areas, subtle against the lighter material.

The crop is still quiet. Nothing yet resembles the familiar button mushrooms that will eventually fill the beds. There are no rounded caps and no short stems. Yet the room is not inactive. Beneath the casing, the fungal network continues to develop.

The worker studies one surface, reads another sensor, and adds a brief note to the tablet. The room sign is checked once more. Then the cart begins to move, and its wheel crosses another floor joint.

A soft bump.

Then another.

Every aisle follows the same calm geometry. Metal supports rise beside clear walking spaces. Shelves continue in parallel lines. Dark compost rests beneath lighter casing. Sensors wait at their appointed places. Small beads of moisture shine on cool metal.

The similarity between the rooms is useful, but it is not complete. Each chamber represents a different moment in the repeating cycle. One batch has only recently completed its spawn run. Another has received its casing. Another is approaching the conditions that will encourage mushrooms to form.

Together, the separate rooms support steady production through the week. They also allow each batch to receive the conditions suited to its present stage, without forcing the whole farm to move at once.

The worker reaches the end of the aisle and pauses. Behind her, the shelves recede in long, even lines. Ahead, another insulated door waits beneath a small sign.

Beneath the lighter casing layer, the mycelium has reached a new stage. Soon, the air will be changed by degrees. Fresh air, moisture, and temperature will be guided toward a different balance.

And across the pale surfaces, the first small signs of fruiting will begin to appear.

Chapter 7: When Mushrooms Begin to Form

Beyond the insulated door, the next growing room is slightly cooler.

The change is gentle enough to pass almost unnoticed. A low fan continues its steady work. Dim lights rest above long, parallel shelves. Small beads of moisture shine on cool metal, and the dark beds stretch quietly toward the far wall.

Along each bed, the casing looks loose and moist, though not heavily wet. Here and there, fine white traces reach through its uneven surface. They are small signs of the living network below.

This casing was added after the compost had been colonized by button-mushroom mycelium. It is not another rich layer of food. In traditional button cultivation, casing is often based on peat mixed with limestone, or with another material used to adjust its acidity. Its exact composition may vary with local resources and farm practice. In general, however, it remains low in nutrients available to the fungus.

Its purpose is quieter and more subtle.

The casing holds water close to the developing crop. Its loose structure supports the exchange of gases through many small spaces. It also helps create conditions that favor fruiting, as the fungus moves toward the stage when visible mushrooms begin to form.

Yet the casing does not simply force the fungus to produce mushrooms. There is no single layer, signal, or adjustment that explains the entire change. Fruiting comes from the biology of the fungus responding to several conditions together.

We follow one bed toward the far end of the room.

From a distance, its surface appears almost unchanged. Up close, more detail becomes visible. Pale mycelium has grown upward from the compost and into the moist casing. Some of its fine threads have gathered into thicker cords. These are called rhizomorphs.

The word describes their root-like appearance, but they are not roots. Mushrooms are fungi, not plants, and these cords are part of the mycelial network spreading through the bed.

Near one cord rests a tiny, pale knot.

It is only a few millimeters wide. Smooth, rounded, and quiet, it sits against the darker casing. A little farther along, there are several more.

Growers may call these first forms primordia, pins, or pinheads. Each one is the early beginning of a fruiting body. With time and suitable conditions, it may become the familiar white button mushroom that will be picked by hand.

The pins do not arrive everywhere at once.

On an earlier visit, this same bed showed only faint patches of mycelium. Now small rounded forms are scattered across the surface. By the next round, some may be larger and easier to see, while new pins may be appearing nearby.

This is the beginning of a flush. Many mushrooms develop within the same general period, but the flush is never perfectly uniform. The bed follows a shared rhythm without making every mushroom identical.

To encourage this stage, the growers have changed the room by degrees.

The temperature has been lowered. Fresh-air exchange has increased, carrying away more of the carbon dioxide produced within the active bed. The carbon dioxide level falls, while high but controlled humidity helps the casing hold the moisture needed for continued growth.

These adjustments must remain balanced. Air that is too dry can draw moisture away from the casing and crop. Too much water can disturb the casing surface and the small pins developing there. The room must be moist, but moisture must be managed carefully.

Water is therefore applied in measured amounts.

Misting or irrigation follows the condition of the beds. The aim is not to cover the young mushrooms with heavy droplets. It is to maintain a useful reserve within the casing while protecting the delicate new growth above it.

The worker pauses beside the shelf and studies the surface without touching it. Her attention moves from one section to the next. She looks at the moisture of the casing, the distribution of the first pins, and the readings that describe the air around them.

No single reading tells the complete story.

Cooler air alone is not the whole signal. Fresh air alone is not the whole signal. Neither is humidity, casing moisture, or the lower level of carbon dioxide. The crop responds to these conditions together, as well as to the state of the mycelium itself.

Above the beds, the dim lights remain steady. They help workers inspect the crop and move safely along the aisles. Strong light is not a primary fruiting trigger for button mushrooms. Darkness alone is not what makes this room useful. The careful control of air, moisture, and temperature matters far more.

Other cultivated mushrooms may have different needs. Their responses to light, carbon dioxide, and fresh air are not always the same. A farm cannot treat every fungal species as though it follows one identical pattern.

We return to the first pale knot in the casing.

It has not visibly changed while we watched. Growth is slow enough to escape the eye from one moment to the next. The bed asks for repeated visits rather than constant staring.

By tomorrow, the difference may be clearer. Once rapid expansion begins, a mushroom can enlarge noticeably over a day or two. Even then, it does not appear fully formed in minutes. Its development remains gradual, taking place across the quiet hours between one inspection and the next.

Harvestable button mushrooms may begin to appear roughly eighteen to twenty-one days after the casing is applied. The exact timing varies. The strain matters, and so do the compost, casing, temperature, airflow, moisture, and methods used on the farm.

Even within one bed, readiness comes in stages.

One mushroom may remain a tiny pin while another nearby has become a firm white button. Workers will return repeatedly during the flush, selecting mushrooms as they reach the desired maturity. Those that are not yet ready will remain in place and be given more time.

For now, no picking is needed here.

The worker makes one more slow observation. The fans continue their subdued rhythm. Moisture rests within the casing, and the first pale buttons hold their places across the dark surface.

Their arrival calls for neither excitement nor alarm. It calls for another careful round. A look at the readings. A note on a chart. A small adjustment, if one is needed. Then the quiet, patient attention of the night shift.

Chapter 8: The Night Shift

The night shift begins without ceremony.

A door closes softly at the end of the corridor, and clean boots cross a sanitation mat. Beyond it, the ventilation fans continue their steady work. Their low sound follows the workers from room to room, as constant as the cool air moving through the tunnels.

Mara, the night grower, puts on a clean outer coat and covers her hair before entering the production area. At the sink, she washes and dries her hands. In rooms where farm policy requires gloves, she adds a clean pair.

Gloves provide a useful barrier, but they do not replace handwashing. Hands or gloves must be cleaned before work, and again whenever they may have touched an unclean surface.

These routines are ordinary parts of food production. So are the clean garments, sanitation mats, and rules about which doors may be used. They are not signs that anything unusual has happened. They simply help keep every production area orderly.

The farm is divided into zones. Compost preparation belongs to one zone. The growing rooms belong to another. Harvest and packing spaces are managed separately again.

Movement between them is controlled because compost fragments, soil particles, and microorganisms can travel on hands, tools, wheels, and clothing. A cart used in one part of the farm may be cleaned before it enters another. Some tools remain assigned to a single room or task.

At the shift station, Mara collects a tablet and a clipboard. The electronic system holds the current environmental readings. The paper sheet offers a simple place for observations.

Automated sensors can measure many things, but an experienced grower still studies the crop directly.

Her first round takes her to a room where the casing layer was added several days ago. She checks the room temperature, then places a clean probe into the compost. The air and the growing medium do not always hold the same amount of heat. Mycelium remains active inside the beds, releasing warmth as it grows and uses nutrients.

Comparing the air and compost temperatures helps Mara understand what is happening beneath the surface.

She waits for the number to settle. A pen moves across the clipboard. Then she continues to the next bed.

The probe, like the farm’s thermometers, scales, and environmental sensors, must be calibrated regularly. Calibration means checking an instrument against a trusted standard to make sure its readings remain accurate. A small error may seem unimportant. Repeated across many rooms and many days, however, it could lead to poor decisions.

The date of each calibration is recorded, along with any adjustment or repair.

Under the dim work lights, Mara bends over the casing. The dark layer appears evenly moist. Small beads of water rest in a few places, but there are no broad pools. She touches only where the inspection procedure allows, looking for the texture and color that experience has taught her to recognize.

A sensor can report relative humidity. It cannot fully describe how the casing looks after irrigation, or whether one corner of a bed is drying more quickly than another. Growers combine the readings with careful observation. They notice the shape of new pins, the firmness of developing caps, and subtle differences in moisture across a room.

At the wall panel, Mara reviews the ventilation schedule.

Fresh air removes carbon dioxide produced by the crop. It also helps manage heat and humidity. Too little air exchange can affect mushroom form and development. Too much may dry the casing.

Tonight, only a minor adjustment is needed. Mara changes the setting by a small amount, then records what she has done and why.

Nothing changes suddenly. The fans continue at their measured pace.

Farther along the tunnel, Tomas prepares the harvest station. He cleans a cart, checks the empty containers stacked upon it, and examines a wheel that made a faint clicking sound earlier in the evening. He adjusts a latch before it can begin to rattle.

The clicking stops, and the corridor becomes quiet again.

At a nearby desk, Tomas lays out labels for the rooms scheduled to be harvested. Each label carries a product code. That code can connect a packed container to its harvest date, growing room, crop batch, or the incoming material lot used to prepare the compost.

If the farm later needs to review quality, trace a delivery, or compare one crop with another, the records provide a clear path backward.

A scanner gives a muted chirp as Tomas tests the first label. He compares the printed code with the night’s harvest list, then places the label beside an empty container.

Across the shift, these tasks repeat in calm rounds.

Environmental readings are checked. Room and compost temperatures are compared. Casing moisture is inspected. Ventilation and irrigation schedules are reviewed. Tools are cleaned and returned to their proper places.

In mature rooms farther down the corridor, mushrooms are harvested. Filled containers are then moved toward cooling. Notes gather line by line on clipboards and screens.

From time to time, the workers exchange a few quiet words.

A room number.

A cart location.

A reminder that one bed will need another inspection before morning.

Occasionally, an alarm record is reviewed. Most alarms are practical notices. A door may have remained open longer than intended. A reading may have moved outside its chosen range. A piece of equipment may be due for inspection.

Like clean clothing and batch records, alarms are ordinary tools of careful food production. They help the workers notice small changes early. There is no rush in the corridor. Only a note, a check, and, when necessary, a measured response.

Mushrooms do not biologically require people to work at night. The night schedule is an operational choice. It may allow the farm to harvest before morning deliveries, use packing equipment efficiently, or maintain continuous oversight across many growing rooms.

The fungus follows its conditions, not the clock on the wall.

Mara begins another round. Again, her boots cross the sanitation mat. Again, a door opens and closes gently behind her. The fans remain steady, and droplets rest along the edges of the beds.

Near the end of the inspection, she enters a room where the crop has become dense and white. She pauses beside one bed and studies the surface.

The caps here are rounded, firm, and still closed beneath their pale veils. Smaller buttons remain between them. Those will be left in place, waiting for another round and a little more time.

Mara compares the bed number with the harvest list. She checks the crop once more, makes a brief note, and calls softly to Tomas.

The cart is ready. The containers are clean. The labels are waiting.

These mushrooms have reached their moment.

The next task will be done carefully, one by one, by hand.

Chapter 9: Harvest by Hand

Tomas approaches the bed with a shallow container resting against one hip. Under the dim work lights, the white mushrooms seem almost luminous. Their caps rise from the dark casing layer in rounded clusters. Some are no wider than a coin. Others are broad enough to fill the palm.

Mara puts on a fresh pair of gloves and reaches toward one of the larger mushrooms. She does not hurry. Her fingers curve lightly around the cool, smooth cap, careful not to press its surface or brush against the smaller mushrooms nearby.

The movement is simple, though it takes practice to perform well.

A gentle bend. A small twist. A quiet lift.

The mushroom comes free with a faint release.

A little compost clings to the base of its stalk. Mara holds the mushroom over a trimming tray and draws a short knife across the end. One neat stroke removes the compost-bearing tip.

Pickers sometimes refer to this trimmed piece as the mushroom’s root, but it is not a botanical root. Fungi do not have roots as plants do. The mushroom is a fruiting body. The larger fungal organism continues through the growing medium as mycelium.

Mara places the trimmed mushroom into the shallow container. She does not drop it. The cap settles gently beside the first mushrooms of the night.

Fresh-market button mushrooms are still commonly harvested by hand. Across a single bed, individual mushrooms mature at different times. One may be ready now, while the smaller one beside it may need another day. Human fingers can judge each mushroom separately and remove it without crushing its neighbors.

Farther along the bed, Tomas begins his own section. His hands repeat the same calm sequence.

Bend. Turn. Lift. Trim. Place.

The work has a steady rhythm, but it is not mechanical. Every cluster is slightly different. Where mushrooms stand close together, Tomas chooses an angle that leaves the surrounding caps untouched. Where one cap leans beneath another, he adjusts his grip and draws it free along the open side.

Most of the mushrooms selected tonight have rounded, closed caps. Beneath each cap is a thin membrane called the partial veil. At this stage, the veil still joins the edge of the cap to the stalk, covering the developing gills underneath. For the familiar white button mushroom sold fresh in shops, an intact veil and a closed cap are common signs of the preferred maturity.

Size alone does not tell the whole story.

A mushroom can become quite large while its cap remains closed and firm. Such a mushroom may still meet the farm’s fresh-market target. Another mushroom, perhaps smaller, may already have begun to open. The pickers consider both size and maturity, along with appearance and the grade requested by the customer.

The crop in this room is *Agaricus bisporus*. The white button mushroom belongs to this species, but so do two other familiar market forms. Brown cremini mushrooms are also *Agaricus bisporus*, sold as a brown, relatively closed form. Portobellos are the same species allowed to become larger and more open, with broad caps and exposed gills.

Here, however, the harvest list calls for closed white buttons.

Mara leaves the smallest mushrooms in place. By the next picking round, some will have reached the chosen size. Their uneven development is expected. A bed is not harvested only once, and the pickers will return.

Button mushrooms tend to appear in recurring waves known as flushes. During a flush, many fruiting bodies develop over a similar period, though not at precisely the same moment. A common pattern may include two to four picking days within a flush cycle lasting roughly seven to ten days.

The workers return repeatedly during that time, selecting only the mushrooms that are ready. The smaller caps remain in the bed, surrounded by humid air and the low, steady movement of ventilation.

After a pause, the bed may produce another flush. The first two flushes often provide the largest share of the crop. Later flushes may yield less, with more open space between mushrooms. Even then, the same careful judgment continues. Each suitable cap is gathered on its own.

The rate of picking changes from bed to bed. Large mushrooms in open groups can be gathered more readily than small mushrooms packed into dense clusters. Bed width, shelf height, mushroom density, desired grade, and the need to protect neighboring caps all shape the pace.

Tonight, no one measures success by the quickest hands. Quality depends on an unhurried touch.

The quiet work continues along the aisle. Cool caps meet lightly curved fingers. There is a small turn, a faint release, and a short trimming stroke. Then each mushroom is lowered into its container.

The shallow trays gradually fill in orderly rows. Their shape helps prevent too much weight from resting on the mushrooms below. Button mushrooms bruise easily, and a firm impact can leave a mark on a pale cap. Each one is placed with nearly the same care used to remove it.

Not every mushroom species is harvested in this way. Oyster mushrooms, shiitake, and other cultivated species may be cut from clusters or blocks, depending on the species and the production system. The gentle bending and twisting movement used tonight belongs to the button-mushroom practice at this farm.

Nor will every mushroom be washed immediately after harvest. Many fresh-market mushrooms are packed dry. Careful cultivation, clean handling, neat trimming, and protection from excess moisture help prepare them for the next stage.

Mara reaches the end of her section and pauses. She looks back over the bed, checking the places where larger mushrooms once stood. In the newly opened spaces, smaller buttons remain tucked between grains of casing material.

She does not disturb them. They will stay in the controlled room, receiving humid air and quiet ventilation. When they are ready, the pickers will return and repeat the same patient movements.

Tomas makes one final trimming stroke and places another mushroom into the nearest tray. The pale caps rest together without being crowded. Their stalks are cleanly trimmed, and their veils remain closed.

He lifts the first full container with both hands. Another is nearly ready beside it. Behind them, the fans maintain their subdued rhythm, and droplets remain along the edges of the beds.

The harvest has not emptied the room. It has only selected what is ready tonight.

Soon, the shallow containers will leave the cool, humid growing chamber. Their pale caps will pass through the doorway toward a brighter room, where weight, temperature, and time begin to matter.

Chapter 10: From Tunnel to Packing Room

Tomas carries the first shallow tray through the doorway. Mara follows with another, and the night’s harvest leaves the dim growing room in a quiet procession. Behind them, smaller mushrooms continue their patient development beneath the low work lights. Ahead, the corridor leads toward the packing room, where the air is cooler and the surfaces are smooth, pale, and easy to clean.

The mushrooms have been separated from the growing bed, but they have not become inactive. They continue to respire, taking in oxygen and releasing carbon dioxide, water vapor, and a little heat. Their tissues continue to develop after harvest.

Cooling slows this activity and helps preserve their quality. It does not stop every biological process, but it gives the workers more time. That is why the journey from the growing room to the cooling area is kept short.

At the packing-room entrance, Tomas places his tray on a stainless-steel table. A label beside it identifies the growing room, bed, harvest date, and shift. This information will remain with the mushrooms as they are sorted, packed, and prepared for delivery. If a question arises later, a lot code can guide the farm back through its records.

Under the brighter lamps, each pale cap can be seen clearly. Workers examine the mushrooms for size, maturity, shape, color, cleanliness, and signs of handling damage. Most of tonight’s buttons are firm and evenly rounded. Their caps remain close to their stalks, and the delicate veils beneath them are still unbroken.

A few need another light trim. Mara uses a clean knife to remove a trace of casing material from the base of a stalk. She works slowly, touching the mushroom only as much as necessary.

Button mushrooms have a high water content and a tender structure. Rough pressure can leave bruises, which may later appear as brown discoloration. The workers therefore avoid dropping, squeezing, or piling the mushrooms too deeply.

Even the sounds of the packing room reflect this care. Containers settle softly on the tables. Scales give brief electronic tones. Clean knives touch the work surfaces with small, muted taps. Through it all, ventilation moves in a low and continuous current.

The mushrooms are divided into grades according to the farm’s customer orders. Some of the small, evenly closed buttons are destined for retail packs. Larger mushrooms will be placed in food-service containers for restaurant kitchens.

Shape and maturity matter, but the grading does not mean that one size is always better than another. Different kitchens, shops, and markets simply ask for different things. The purpose is to make each container consistent and suitable for the person who will eventually use it.

At one station, a worker places an empty container on a scale and returns the display to zero. Mushrooms are added one by one until the required weight is reached. The container is not overfilled. Crowding would place unnecessary pressure on the caps, increasing the chance of bruising.

A clear film is fitted over each retail pack. Tiny perforations in the film are almost invisible, yet they serve an important purpose. The covering helps reduce moisture loss while still allowing gas exchange.

A completely open package could allow the mushrooms to dry too quickly. A poorly chosen sealed environment could allow moisture and gases to accumulate in undesirable ways. The film helps create a modest balance around a product that is still living and respiring.

Moisture is especially important. Fresh mushrooms contain a great deal of water, and they lose it readily. If the surrounding air is too dry, their surfaces may become dull. The caps can darken, and their edges may begin to curl.

Yet the answer is not simply to make the air as damp as possible. Suitable humidity must be combined with careful temperature control, ventilation, clean equipment, and gentle handling. Each condition supports the others.

When a pack reaches the correct weight, it receives its label and lot code. The code connects it to this night’s harvest and to the room and bed where it grew. The finished packs gather in clean crates, arranged so that the containers underneath do not bear too much weight.

Mara pauses beside one crate and checks the labels against the harvest record. The movement is familiar and unhurried. One line is confirmed, then another. When the count is complete, the crate is carried toward the cooling area.

The farm uses forced-air cooling. Chilled air is drawn through openings around the containers, carrying heat away from the newly harvested mushrooms. This cools them more quickly and evenly than leaving the crates in still air.

For fresh *Agaricus* mushrooms, the cultivated button mushrooms grown in these tunnels, a well-established postharvest recommendation is approximately 32 to 35 degrees Fahrenheit, or 0 to 1.5 degrees Celsius, with relative humidity around 95 to 98 percent.

Individual farms may use somewhat different targets, depending on their equipment, packaging, handling methods, and distribution plans. The recommended range is a respected guide rather than a single inflexible rule.

Near 35 degrees Fahrenheit, or about 1.5 degrees Celsius, carefully handled mushrooms may retain good quality for roughly five to seven days. Even so, no temperature can guarantee an exact storage life. Variety, maturity, packaging, bruising, travel time, and changes in conditions along the route all have an effect.

The cold room is reserved for compatible goods. Mushrooms can absorb strong surrounding odors, so mixed storage requires care. Here, the air smells faintly clean and earthy. Strongly scented produce and other sources of powerful odors are kept away.

Crates now stand in orderly rows beneath the quiet current of chilled air. They are not forgotten while they cool. Their temperatures and labels will be checked before loading, just as the growing rooms were checked throughout the night.

By dawn, tonight’s harvest can be cool enough to enter a refrigerated vehicle. Some packs will travel to neighborhood shops or local markets. Larger food-service containers will continue to restaurants and other kitchens.

There, the mushrooms may be sliced, sautéed, roasted, or added to soups and sauces. Their destinations differ, but each journey begins with the same careful sequence: inspection, trimming, grading, weighing, packing, coding, and cooling.

For now, they wait beneath the soft flow of cold air. Their passage through the underground farm is nearly complete.

Behind each label lies a longer story. Prepared compost filled the beds. Mycelium spread quietly through the growing medium. Mushrooms formed beneath humid air and low work lights. Skilled hands selected only those ready for harvest, leaving the smaller buttons undisturbed.

Now the pale caps rest in their containers, protected from rough pressure and unnecessary drying. Tomas brings in another shallow tray. Mara makes room beside the scale. A label is printed, a weight is confirmed, and another crate joins the waiting rows.

The work continues without hurry. Above the farm, the last hours of darkness pass over the hill. Below it, chilled air moves through the packed containers, carrying away the remaining warmth of the harvest.

Ahead lies the measured road toward morning.