PF Tek Explained: A Beginner’s Guide to Mushroom Cakes

PF Tek is a beginner-friendly cultivation method that uses small jars filled with brown rice flour, vermiculite, and water. The jars are heat-treated, inoculated with mushroom culture, and kept closed while the mycelium colonizes the mixture.

Once the contents are fully colonized, the solid block is removed from the jar. That block is the “cake” — a self-contained puck of mycelium and food that can be fruited on its own, usually resting on a tray or foil inside a humid chamber.

The name comes from the method’s originators, but you do not need to know its history to use it. The useful idea is that each jar holds one isolated, protected grow, and each cake is a complete fruiting unit.

If the vocabulary is new to you, our plain-language guide to mushroom-growing terms explains mycelium, colonization, fruiting, and flushes before you start.

PF Tek earns its beginner reputation for three reasons.

• The materials are inexpensive and easy to find: jars, vermiculite, brown rice flour, water, and a basic fruiting container.
• Each jar is isolated. If one jar contaminates, the others can still succeed, so a single failure does not end the whole grow.
• It teaches the full life cycle — inoculation, colonization, fruiting, and harvest — in a compact, observable form.

The tradeoff is output. A PF Tek cake produces a modest amount of mushrooms compared with a fruiting block, a bucket of straw, or a stack of logs. If your goal is volume, other methods will serve you better once you understand the basics.

If your goal is to learn, though, few methods are as forgiving or as instructive.

A basic PF Tek setup uses:

• Small wide-mouth jars with lids (wide-mouth jars make birthing the cake easier)
• Clean vermiculite
• Brown rice flour
• Clean water
• Aluminum foil
• A covered pot for steam treatment, or a suitable pressure cooker
• A clean, draft-free workspace for inoculation
• A suitable legal gourmet mushroom culture from a reputable supplier
• Optional: a clear plastic tub and perlite for fruiting

Follow your supplier’s storage and handling instructions for the culture, and use it while it is healthy and active. Do not use wild mushrooms as your starting culture.

For a broader look at indoor-jar and cake supplies, see our tools and supplies guide.

A widely used starting ratio by volume is about:

• 2 parts vermiculite
• 1 part water
• 1 part brown rice flour

Add the water to the vermiculite first and mix it through before adding the brown rice flour. That lets the vermiculite absorb the water evenly so the flour coats damp particles rather than forming wet clumps.

Treat this as a starting point, not a commandment. Vermiculite grade, flour freshness, and jar size all change how the mixture behaves. Adjust the moisture until the mix holds together when squeezed without dripping water, then follow a tested recipe for your exact materials.

At its simplest, the process is:

1. 1Prepare small wide-mouth jars and lids.
2. 2Mix the vermiculite, water, and brown rice flour, then fill the jars loosely.
3. 3Wipe each rim clean and add a dry vermiculite barrier on top.
4. 4Cover the jars with foil and put the lids on.
5. 5Heat-treat the jars.
6. 6Let them cool completely.
7. 7Inoculate each jar with a suitable legal gourmet culture in a clean, draft-free workspace.
8. 8Let the jars colonize undisturbed.
9. 9Wait for full colonization plus a short consolidation period.
10. 10Birth the cakes from the jars.
11. 11Optionally dunk and roll the cakes.
12. 12Fruit them with humidity, fresh air, indirect light, and a species-appropriate temperature.
13. 13Harvest using the guidance for your species.

The sections below fill in the parts that benefit from more care.

The goal of heat-treating is to reduce competing organisms in the jars before you introduce your mushroom culture.

Because PF Tek jars are small, many traditional instructions treat them with atmospheric steam in a covered pot with a raised trivet or lid. Keep the water level steady, vent as little as possible, and follow a tested schedule for your jar size and load.

A correctly used pressure cooker provides a larger safety margin because pressurized steam reaches higher temperatures than boiling water alone. No single schedule fits every jar, load, altitude, or cooker, so use a procedure written for your exact equipment and recipe.

We’ve used a Presto pressure cooker for brown-rice-flour jars at roughly 12–15 psi for about an hour, give or take, and it has worked at our small scale.

Treat that as a description of our own experience, not a universal validated schedule. Jar size, fill depth, elevation, and the recipe itself all matter. Follow the pressure cooker or canner manufacturer’s safety directions and your supplier’s guidance, and never run a cooker dry or open it while it is still under pressure.

For the broader context on when cleaning, pasteurization, or pressure sterilization applies, see clean, pasteurized, or sterile growing.

Once the jars are completely cool, they are ready to inoculate. Introducing culture to a warm jar can kill it, so patience here pays off.

Work in a clean, draft-free space: still air, washed hands, sanitized surfaces, and no fans or open windows. PF Tek does not require a laboratory, but this is the moment when careless handling can undo the benefit of heat-treating.

Use a suitable legal gourmet culture and follow the supplier’s inoculation guidance. Work efficiently and keep the jars open for as short a time as practical.

Place the inoculated jars in a clean spot out of direct sunlight, at a temperature suited to your species. Then leave them alone.

Over the following weeks, white mycelium should spread through the substrate. The exact timing depends on the species, culture vigor, temperature, and how densely the jars are filled.

Resist the urge to open the jars repeatedly to check progress. Every opening introduces fresh air and organisms from the room. Look through the glass instead.

When the substrate appears fully colonized, wait a little longer. A short consolidation period lets the mycelium strengthen internally before it has to fruit. Follow your supplier’s recommendation for how long to wait.

When a cake is fully colonized and consolidated, birth it by sliding it out of the jar. Wide-mouth jars make this step straightforward; narrow rims can trap the cake.

Inspect each cake before fruiting it. A healthy cake is dense and white. Discard cakes with extensive green, black, pink, orange, or slimy growth rather than fruiting them. Do not deliberately smell questionable substrate.

Optional: dunk and roll

Many growers rehydrate a cake by briefly soaking it in clean, cold water (a “dunk”) and then coating it with a thin layer of clean vermiculite (a “roll”). The vermiculite holds moisture against the cake’s surface and gives mushrooms more places to pin.

This step is optional and should follow a tested procedure for your species. Clean water and clean handling matter throughout.

A basic fruiting chamber can be a clear plastic tub with a shallow layer of damp perlite in the bottom.

1. 1Add roughly a half-inch layer of perlite and moisten it with clean water.
2. 2Set each cake on its own square of foil, lifted slightly above the perlite.
3. 3Never rest a cake directly on the perlite or in standing water.

Porous, damp perlite exposes a large amount of water to the air, which raises the humidity inside the tub through evaporation. It increases the evaporative surface area, but it does not replace fresh air. Mushrooms still need ventilation, so do not seal the tub airtight.

For more on balancing humidity with fresh air, see whether mushroom growers really need a humidifier.

Humidity advice can sound universal, but growers are not all starting with the same air.

Humid Virginia summer air, a heated winter room, a cool basement, and an air-conditioned kitchen all behave differently. The same tub may hold moisture easily in one season and dry out quickly in another.

Rather than chasing one perfect number, judge the surfaces and the growth. Young mushrooms should look plump and develop normally, not shrivel or crack. The chamber should feel humid, not soaking wet, and the air should not be stale.

Constantly wet mushrooms and trapped, stale air are not the goal. If water pools on the caps or visible surfaces stay saturated, reduce moisture and increase air exchange.

Choosing where to put the tub matters as much as the tub itself — see our guide to placing a mushroom grow.

A healthy PF Tek run moves through a recognizable sequence.

• White mycelium appears at the inoculation points within days to a couple of weeks.
• The mycelium spreads outward and eventually fills the jar.
• After full colonization and a short rest, the cake holds together as a solid white block.
• Once birthed and fruited, small pins form on the cake and develop into mushrooms.
• After harvest, the cake rests and may produce another flush.

Progress is rarely perfectly uniform. Slightly different speeds between jars are normal. What matters is steady, healthy growth and the absence of contamination.

Stalled or over-wet jars

If colonization stops early, the substrate may be too wet, packed too tightly, or sitting at the wrong temperature. Over-wet jars can leave uncolonized, soggy patches and stalled growth. Review your moisture level, fill density, and temperature rather than assuming the culture failed.

Dry cakes

A cake that dries out after birthing may pin poorly or produce small, cracked mushrooms. A careful dunk can rehydrate it, and a thin vermiculite layer helps hold moisture. Keep the fruiting chamber humid and check the perlite if it dries out.

Poor-air symptoms

Mushrooms grown without enough fresh air often develop long stems and undersized caps. If you see this, increase air exchange while still keeping the chamber humid. Open the tub more often or add filtered ventilation.

Contamination

Green, black, pink, or orange growth, slimy patches, or strong unpleasant odors are warning signs. Handle contamination conservatively:

• Isolate or discard a clearly contaminated jar without opening it indoors.
• Never smell a contaminated jar to identify it.
• Do not try to salvage contaminated food substrate.
• Clean the area thoroughly before starting another batch.

A contaminated jar does not mean the whole method is wrong. Note what happened, clean up, and try again with one change at a time.

Fill small jars with a damp mix of vermiculite, water, and brown rice flour. Heat-treat them, let them cool, inoculate cleanly, and wait while the mycelium colonizes.

Birth the cake, give it humidity, fresh air, indirect light, and a suitable temperature, and harvest when the mushrooms are ready for your species.

You do not need perfect technique or elaborate equipment to learn a great deal. You need clean handling, patient observation, and a willingness to adjust based on what the mushrooms show you.

When the mushrooms are ready, our oyster harvest guide explains how to read cap edges and remove a cluster.

Afterward, our guide to storing fresh mushrooms covers refrigeration, drying, and freezing so your harvest lasts.