Popcorn Mushroom Grain Spawn

November 4, 2025

Using corn

This method doesn’t involve soaking overnight, rather hydrates the corn in a short pressure cooker session so you can do the whole thing in one session. Give yourself a few hours: I’ve been up til 2 AM to turn the heat off way too many times.

Tips for using a pressure cooker/canner

5kg of dried corn produced 14 jars. Still trying to find the right amount for 9-10 jars.

You do not want the aluminum bottom rack in for this step. Cooking corn like this can stain the inside of your pressure cooker, but this probably doesn’t matter. You shouldn’t be pressure cooking food directly on aluminum anyway.

Hydrate popcorn in pressure cooker with at least 2 inches of water above popcorn. Remove floaties during this step: malformed kernels, dust, etc. A small strainer with a handle is good for this. You can’t use too much water for this step (other than it takes longer) – you don’t want the corn to be above the water when you finish. While the cooker is still hot, you might want to wash the inside of the cooker and the lid so you don’t end up with a layer of corn sugars coating the inside.

Bonus: Drippy corn tek: add 1 shot glass of high fructose corn syrup for drippy corn tek.

When you pour it out, you might want to collect some grain water for high nutrient agar later. This isn’t sterile: it could form mold in the fridge if you leave it too long and keep it in a sealed jar.

You don’t want the kernels to be too soft, just rehydrated. You want the kernels to be pretty dry on the outside. The kernels should be soft to crush between your fingers with a little effort. ~~ If they get too soft they’ll end up bacterial from holding too much moisture.

You want the surface to be dry. This can be hastened by splitting between a couple of bowls and flipping while still hot and steaming. Optionally dry on a towel on the counter.

This is a good time to recheck your rubber seal. The batch I did while writing this up had a couple of kernels of corn that had gotten between the gasket and the lid, causing a leak. Between these steps is a good time to clean corn sugar out of the inside of the cooker.

Bag or jar up. Don’t overfill the jars because you will want to be able to shake it up to distribute the culture once it starts. I recommend about 2/3 full for quart jars. Jars should have a hole for air breathing, either use those little porous patches or a couple layers of paper first-aid tape. My jars have another hole covered with a rubber patch (available from many vendors, I like Microppose.com)

cover the tops of the jars with a piece of aluminum foil. At this point, the corn has all the water it’s going to have. The next step is for sterilizing, not hydrating.

Put about 2 quart jars of water in the pressure cooker first. .
Place the jars in the pressure cooker. If you have a tall cooker, you can put two or maybe even 3 jars on their side on top of the seven in the bottom. Spillage shouldn’t be a problem since all the water should be in the kernels.

If you are using bags, the bags should not touch the water. You can make a stand for the bottom with some 2 inch screws and nuts to keep the bags above the water. Putting a ceramic plate on top of bags will help to keep them from expanding during cooking.

Seal the cooker. Use 15# pressure, sterilize 1.5 hr (again, set the timer after the rattling starts). This step isn’t adding any more water. Some folks recommend 2.5 hours, that seems a bit of overkill to me. You should not have any gas escaping except around the rattling regulator.

While the jars are being sterilized is a good time to clean up all the bowls, spoons, funnels to remove corn sugars. Put them away so you have a nice clear spot to put the jars when they come out.

When you remove the jars, shake them a little bit to evenly distribute moisture. There should not be any water at the bottom of the jars.

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