How to make Drippy Corn

Sterilized grain is the launch pad for mushroom cultivation. You inoculate it with clean mycelium from liquid culture, agar, or grain to grain. Let it colonize. Then use the colonized grain to inoculate bulk substrate like sawdust or a sawdust and soy hull mix. Corn is popular because kernels are large and easy to shake, cheap, and readily available.

“Drippy corn” means you stop drying while kernels still have a thin surface sheen. Moist enough that a shaken jar or bag leaves a few scattered droplets. Not puddles. That micro film of water does three useful things.

1. Speeds recovery and growth after shaking. The mycelium finds micro moist interfaces right away.
2. Buffers against over drying during long sterilization runs. Corn can lose surface moisture in the pressure cooker.
3. Reduces burst kernels compared to prolonged simmering aimed at ultra dry surfaces.

The goal is hydrated through kernels with intact hulls, no pooled water, and a slight glisten. Drippy, not soggy.

Batch size and planning

• Target output. 6 bags × 3 lb hydrated equals 18 lb (≈8.2 kg) hydrated corn.
• Typical hydration uptake for whole corn is ~1.7–2.0× dry weight.
  • Practical shopping math. Plan on ~10–11 lb dry corn to finish at 18 lb hydrated. Buy 12 lb to have margin and learn how your corn behaves.

Jar equivalence. A wide mouth quart jar holds ~650–700 g hydrated corn. One 3 lb bag ≈ 2 quarts. The whole batch ≈ 12 quart jars.

Gear and supplies

Grain and prep

• Whole dry corn feed or food grade. Buy 12 lb.
• Gypsum calcium sulfate. Optional but helpful. 1–2% of dry grain by weight. ≈50–100 g for 5 kg.
• Large stock pot 16–20 qt is comfortable.
• Colanders or large mesh baskets.
• Large trays or racks or window screens for steam drying.
• Clean towels or paper towels.

Containers

• Unicorn 4T or 4T-INJ filter patch bags 0.2 µm filter.
  • For LC injection use 4T-INJ or add a self healing injection port.
• Mason jars wide mouth quarts with two piece or plastic lids.
  • Lid filters. SFDs, 0.2 µm filters, or lids with a filter hole and self healing injection port.
  • If you lack SHIP or filters you can do agar wedges in a SAB or hood. Filtered lids are strongly recommended.

Sterilization and sealing

• Presto 23 qt pressure cooker Model 01781 or 01784 or equivalent.
• 15 psi weight or regulator and intact overpressure plug.
• Rack or trivet plus spare jar rings to elevate bags.
• Accurate timer and kitchen scale.
• Impulse sealer for bags or clamps if sealing post sterilization in a hood or SAB.
• Heat resistant gloves.

Clean technique and inoculation

• Still air box or laminar flow hood.
• 70% isopropyl alcohol, paper towels, and nitrile gloves.
• Flame or micro sterilizer for tools.
• Sterile LC, clean agar wedges, or G2G donor grain. Beginners usually start with LC.

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Safety notes

• Keep the vent pipe clear. Always vent 10 minutes before placing the weight.
• Never let the pot run dry. Start with ~2–3 inches water in the Presto. For bags use ~3 inches.
• Confirm gasket and overpressure plug are in good shape.
• Let the cooker depressurize naturally. Do not force cool with bags inside.
• Hot grain burns. Use gloves.

Overview of the process

1. Rinse and soak the corn to hydrate and wake endospores.
2. Simmer to finish hydration until plump and not bursting.
3. Drain and steam dry the surface to drippy sheen with no puddles.
4. Load into bags or jars. 3 lb per bag. ~650–700 g per quart.
5. Seal and sterilize. Bags 2.5–3.0 h at 15 psi. Jars 90–120 min at 15 psi.
6. Cool fully. Inoculate cleanly. Incubate.
7. Shake once at 20–30% colonization. Finish and use as spawn.

Step by step. Hydrate and prep the corn

1) Rinse and sort

• Weigh ~11 lb dry corn to target ~18 lb hydrated.
• Rinse thoroughly in a large pot or bucket.
• Skim floaters and debris. Discard.

2) Soak 12–18 hours

• Cover with warm water by 2–3 inches.
• Add gypsum at 1–2% of dry grain weight.
• Soak 12–18 hours at room temp.

Checkpoint. After soak, kernels are larger and cut with a fingernail. Not squishy.

3) Simmer to finish hydration

• Drain the soak water. Refill with fresh water a couple inches above the corn.
• Bring to a gentle simmer. Avoid a rolling boil.
• Simmer ~25–45 minutes until fully plump and the germ tip is soft.
  • Stop before many kernels burst. A few splits are okay.

Test. Slice a kernel. The center should be uniformly hydrated not chalky. Squeezable but not mush.

4) Drain and steam dry to “drippy”

• Drain in colanders 5–10 minutes.
• Spread on trays or racks in a single to double layer.
• Steam dry 20–40 minutes with a toss every ~10 minutes until the surface is shiny but not pooling.
  • Hand test. Scoop and tilt. No puddle. Light sheen. If you load a jar and shake you should see a few isolated droplets on the glass.
  • If you see puddling keep drying. If kernels look matte and dusty you over dried. Lightly mist and toss to bring the sheen back.

Bag method. Unicorn 4T or 4T-INJ

5) Weigh and bag

• Weigh ~3.0 lb drippy corn per bag.
• If no injection ports and you plan LC, install SHIPs ahead of time or plan agar wedges in a hood after sterilization.

6) Add headspace and fold

• Shake grain below the filter patch.
• Fill to ~1/2 to 2/3 full so you can shake later.
• Hockey stick fold. Flatten gussets. Fold the top over twice. Then
  • Impulse seal above the filter patch before sterilization or
  • Fold and clip for sterilization and do a final seal post sterilization in the hood.

Tip. If pre sealing some use a thin Tyvek strip in the seal to help equalize pressure. Many just pre seal cleanly. The 0.2 µm patch usually handles equalization.

7) Load the Presto for bags

• Place the rack. Add ~3 inches water.
• Use jar rings under a wire rack to create an air and water gap. Keep bags off the bottom.
• Arrange 2–3 bags upright. Do not press filters to the pot wall. Leave steam pathways.
• Bring to a boil with the lid on but unweighted until a solid vent of steam escapes. Vent 10 minutes.

8) Sterilize the bags

• Place the 15 psi weight after venting.
• At 15 psi start the timer.
  • 2.5–3.0 hours at 15 psi for 3 lb corn bags.
• Adjust heat so the weight rocks gently and the gauge stays near 15 psi.
• Turn off heat. Let depressurize naturally.

9) Cool and store

• When pressure reads zero open the lid away from you.
• Cool to room temp on a clean surface.
• If folded or clipped move to the hood and impulse seal now.
• Store at room temp up to 1–2 weeks. Best practice. Inoculate within a few days.

Jar method. Wide mouth quart jars

10) Fill and lid up

• Load each quart with ~650–700 g drippy corn. About three quarters full.
• Wipe rims. Install lids with filter and SHIP if injecting LC.
• Band tightness. Snug finger tight. Do not wrench down.

11) Load the Presto for jars

• Rack in and ~2–3 inches water.
• Seven quart jars fit per run in a Presto 23 qt. This batch is ~12 quarts. Plan two runs.
• Vent 10 minutes before weighting.

12) Sterilize the jars

• Process at 15 psi for 90–120 minutes. Use 120 for corn.
• Maintain gentle rocking of the weight near 15 psi.
• Let cool and depressurize naturally.

Inoculation

Work cleanly in a SAB or flow hood. Wipe surfaces, gloves, and ports with 70% ISO. Flame sterilize needles for LC.

Option A. Liquid culture

• Bags with SHIP or jars with SHIP. Inject 2–5 mL LC per 3 lb bag or per quart.
• Use multiple small injections in different spots.
• Swab ports with ISO before and after. Flame between containers. Cool by pushing a drop before the next port.

Option B. Agar wedges

• In the hood crack the mouth and drop a rice grain to pea sized clean wedge.
• Reseal bags or tighten lids.

Option C. Grain to grain

• Only if the donor grain is fully clean.
• Transfer ~1–2 tbsp into each receiving container. Seal promptly.

Incubation and first shake

• Temperature. 68–75 °F is ideal. Warmer is not faster past ~75 °F.
• Light. Irrelevant for colonization.
• Shake. At 20–30% colonization shake vigorously to distribute.
  • Bags. Smack the bottom edge on a padded surface and massage.
  • Jars. Smack and roll to break clumps.
• Expect a quick rebound in 24–72 hours. Full colonization in 7–14 days depending on culture, temp, and injection points.

Drippy corn helps here. The slight surface moisture bridges gaps after the shake.

Using your finished grain spawn

At 100% colonization you can inoculate bulk substrate. Break up the spawn right before mixing to maximize inoculation points.

Troubleshooting

Many burst kernels after simmer

• Simmered too hot or too long. Keep it gentle. Burst kernels invite bacteria.

Pooled water in containers

• Loaded too wet. Next time dry to drippy. For this batch you can shake mid colonization to redistribute. Pooling raises risk.

Slow or no recovery after shake

• Over dry or over wet can stall. Hit the drippy target. Check temp. Verify inoculant is clean and viable.

Sour smell or wet slime

• Under sterilization, very wet grain, or dirty inoculant. Extend time for corn to 2.5–3 h at pressure. Always vent 10 minutes. Review aseptic technique.

Filters wet from condensation

• Let cool longer in the cooker with lid cracked or on a clean rack. No fans on hot bags.

Bag filter scorched or bag melted

• Bags touched the wall or bottom. Elevate and keep space from sides.

Time and capacity planning with a Presto 23 qt

• Bags. 2–3 bags per run. Two runs equals 4–6 bags.
• Jars. 7 quarts per run. Two runs hit ~12 quarts which equals ~6 bag equivalents.
• Bags need 2.5–3.0 h at pressure plus heat up and cool down. Jars need ~2.0 h at pressure plus heat up and cool down.

Cleaning, labeling, and tracking

• Label strain, inoculation method, and date. Painter’s tape and Sharpie work.
• Keep a simple log. Hydration time. Simmer time. Sterilization time. Inoculant source. Small notes drive improvements.

FAQ quick hits

Why gypsum
It reduces clumping and adds Ca and S minerals. Optional but useful.

Do I add coffee or molasses to corn
No. Plain water and gypsum are enough for grain prep. Save additives for substrate or LC formulas.

How drippy is drippy
Shake a jar. You should see a few scattered droplets on the glass that slide or reabsorb quickly. No puddles. Kernels still separate when shaken.

When should I shake
Once at 20–30%. A second light shake at 60–70% is optional for stubborn clumps.

Complete step checklist

1. Weigh 11–12 lb dry corn. Rinse. Remove floaters.
2. Soak 12–18 h in warm water with 1–2% gypsum.
3. Drain. Simmer gently 25–45 min until fully plump with minimal bursts.
4. Drain 5–10 min. Steam dry 20–40 min to drippy.
5. Bag method. Load 3.0 lb per bag. Pre seal or clip for post seal.
6. Jar method. Load 650–700 g per quart. Install filtered lids and SHIP.
7. Presto setup. Rack in. 2–3 inches water. Load. Vent 10 min.
8. Run at 15 psi. Bags 2.5–3.0 h. Jars 90–120 min.
9. Natural cool. Open away from you. Finish seals if needed.
10. Inoculate in a SAB or hood. LC 2–5 mL per bag or jar or add agar wedge. Swab ports. Flame needles.
11. Incubate 68–75 °F. Shake at 20–30%. Finish to 100%.
12. Use as spawn. Log what worked for next run.

Final calibration tips

• Different corn lots hydrate differently. For a new source run a small test batch. Adjust simmer and drying for the big run.
• Do not complicate hydration. Consistent moisture, proper sterilization, and clean inoculant beat fancy tricks.
• When in doubt on moisture it is safer to be slightly drippy than too wet or too dry. Too wet invites bacteria. Too dry slows colonization.