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BRF PF Tek Calculator

Scale the classic 2:1:1 PF Tek jar recipe to any number of jars and any jar size. Outputs total and per-jar amounts.

Inputs

Jar size (mL)
Standard PF Tek jars are half-pint (240 mL) wide-mouth.
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How the formula works

PF Tek (named after Robert "Psilocybe Fanaticus" McPherson) is the classic BRF cake recipe. It uses a fixed 2:1:1 volumetric ratio of vermiculite, brown rice flour, and water per jar — meaning each jar gets one-half its volume in vermiculite, one-quarter in BRF, and one-quarter in water.

  • Vermiculite = jar size × 0.5 (per jar)
  • Brown rice flour = jar size × 0.25 (per jar, by volume)
  • Water = jar size × 0.25 (per jar)

For a standard 240 mL (half-pint) jar that's 120 mL vermiculite, 60 mL BRF, and 60 mL water. Scale up by multiplying each amount by your jar count. The ratio works because vermiculite holds the water and creates air gaps for mycelial gas exchange, BRF supplies the nutrients, and the water hydrates everything to roughly field capacity.

Brown rice flour is measured by volume in the original tek but most cultivators weigh it for accuracy. We convert volume to grams using a bulk density of ~0.65 g/mL — this is approximate (BRF density varies by grind and brand), so treat the gram figure as a starting point and adjust by feel: the mix should be the consistency of damp, crumb-able snow.

Worked example

Target: 6 standard half-pint jars (240 mL each), classic 2:1:1 ratio.

  • Vermiculite: 6 × (240 mL × 0.5) = 720 mL
  • BRF (volume): 6 × (240 mL × 0.25) = 360 mL
  • BRF (weight): 360 mL × 0.65 g/mL ≈ 234 g
  • Water: 6 × (240 mL × 0.25) = 360 mL

Per jar: 120 mL vermiculite + ~39 g BRF + 60 mL water. Mix the vermiculite and water first until evenly damp, then fold in the BRF last so it stays loose. Fill jars to about a half-inch below the rim, then dry-layer plain vermiculite on top before pressure-cooking at 15 PSI for 60–90 minutes.

We're deliberately not predicting yields here — PF Tek output varies wildly with species, genetics, and dunk-and-roll technique. The math tells you what to put in the jar; what comes out is on you.

When to use this calculator

Use this calculator any time you're prepping BRF cake jars — whether it's your first PF Tek run or you're scaling up to a dozen jars at once. PF Tek is the beginner's go-to for psilocybe species because the cakes are small, forgiving, and don't need a flow hood, but the same recipe works for any spore-to-fruit experiment where you want a cheap, self-contained jar of substrate.

Common mistakes: over-hydrating the mix (the cake should hold shape but not drip — extra water means anaerobic pockets and bacterial blotch), packing the cake too tight (mycelium needs air gaps; pack to a firm-but-springy density, not concrete), and skipping the dry vermiculite top layer (the dry layer is your contamination buffer, do not omit it). Another classic error is opening jars too early to peek — every time you crack the lid you invite contam.

Variations: some growers add ~10% gypsum by weight to the BRF/vermiculite mix for pH buffering, similar to CVG. Whole brown rice flour (ground from whole grain) tends to colonize a touch faster than commercial pre-ground BRF because the bran is still intact, but pre-ground works fine and is more consistent. A few teks substitute oat flour or coco coir for some of the BRF — those are no longer strictly PF Tek but the math here still works as a starting volume.

Frequently asked questions

  • Should I use whole brown rice or brown rice flour?

    Brown rice flour. PF Tek depends on the BRF being finely ground so mycelium can colonize the whole cake evenly. Whole grain brown rice belongs in grain spawn jars, not cakes. If you can't find pre-ground BRF, grind whole brown rice in a coffee grinder or blender until it's the texture of fine flour.

  • How long does PF Tek take to colonize?

    Typically 3–5 weeks from inoculation to fully colonized cake at 21–24°C (70–75°F), depending on species and genetics. Faster isolates may finish in 2 weeks; slower ones can take 6+. Look for the cake to be uniformly white with no uncolonized brown patches, then birth the cakes (pop them out of the jars) and move them to a fruiting chamber.

  • Do I need to soak the BRF before mixing?

    No. PF Tek mixes BRF dry into the damp vermiculite — that's the whole point of the volumetric ratio. Soaking BRF separately gums it up and makes it pack too dense. The water in the recipe is what hydrates everything during the pressure-cook cycle.

  • Can I use PF Tek for non-psilocybe species?

    Yes for many gourmet species, with caveats. Pink and blue oysters, lion's mane, and reishi will all fruit on BRF cakes, though yields are smaller than from a proper bulk substrate. Cold-loving species like enoki and shiitake don't do well on cakes — they need a different substrate (sawdust blocks for shiitake, supplemented hardwood for enoki). For most gourmets, you're better off with grain spawn into a CVG monotub. See our CVG substrate calculator for that path.

Related resources

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