How to Make Sterilized Grain for Mushroom Spawn Production

There are many ways to make sterilized grain, and each method has its pros and cons especially when considering the scale you are going to operate at. We will go over a few methods we find nice for the small grower, intermediate, and larger scale production.

Easiest Method:

Mix the correct amount of water and Sorghum grain together into the bag or jar of your choosing and pressure cooker for 90 minutes once up to temperature. When the 90 minutes is up, let it cool so it loses all of its pressure, is below boiling, and is at a temperature that allows you to handle the bags or jars. Operate the pressure cooker properly, and do not remove the weight until it is no longer under any pressure (once the safety lock drops).

Give the grain a tumble so that the bottom grain which is slightly more moist will mix with the slightly dryer top grain. Doing this while it is still warm to hot will aid in more even distribution of moisture, but ultimately this step is not needed.

Very easy process but be sure you get the water correct: too dry and it will be slow to colonize, too wet and it will have a bit of excess moisture. Both are generally okay but if you hit the extremes of too dry or too wet it can be problematic.

Here are our recommended amounts of water and Sorghum for this process in useful increments for jars and bags:

1 Pint Jars:
125 grams Sorghum
106 grams Water

1 Quart Jars:
250 grams Sorghum
213 grams Water

3 lbs Bags
760 grams Sorghum
650ml of Water

6 lbs Bags
1520 grams of Sorghum
1300 grams of Water

Sterilized Grain: What Grain Is Best?

For the production of mushroom spawn, Sorghum is probably the best choice.

Interested in buying Sorghum? Click here!

Explanation & Reasoning:

The goal of grain spawn is to provide many points of inoculation, in certain circumstances nutrition that compliments the substrate, and colonize rapidly so that you can have a faster turnover.

In order to provide many inoculating points throughout the bulk substrate, you want a smaller grain as that provides, pound-for-pound, more inoculating points. A single pound of millet for instance will provide vastly more surface area and inoculating points than corn.

Not all grain spawn needs to provide nutrition; such as when growing oyster mushrooms on the master mix. The master mix has plenty and adding more spawn won’t be of much benefit beyond faster colonization times. Often times a large 5 lbs bag of master mix only needs a few tablespoons worth of grain spawn to colonize rapidly and perform well.

However, when growing Psilocybe species on CVG or other bulk substrate, the grain spawn provides most of the nutrition. Instead of a few tablespoons worth, the colonized grain spawn is in a ratio of 25% to 50% vs the bulk substrate.
In this scenario, you’d want a grain that is high in protein, starch, and various fats and minerals.

The best grain is small, highly nutritious, cost-effective, and fast to colonize. We think Milo is the best option as it ranks well in all those aspects, but millet, rye, and oats are also great options.

Corn seems to be trending in the grain spawn scene but I don’t understand the logic beyond that it is visually pleasing when colonized.

Don’t overcomplicate it!

People love to get lost in the weeds with making sterilized grain, and there is a lot of misinformation going around. Some of the biggest misunderstandings come from the idea that the presence of excessive moisture, such as from condensation or burst grains leads to contamination. They do not, but they can make contamination more obvious. Excessive moisture and burst grains are annoying for many reasons; it can make it difficult to shake or break apart once colonized, but they do not cause contamination. Contamination comes from improper sterilization, faulty filters, or spawn bags that let contamination in.
People will often see burst grains once they hydrate the grain and worry that it will cause big issues for them. If they have a good bag or jar and properly sterilize it, the grain will colonize just fine.

The same goes for moisture: even if you have perfectly and evenly hydrated grain, moisture can still form: taking it out of the hot sterilizer and into a colder room is going to cause the moisture to condense on the bag to some degree. This is resolved by letting it reach room temperature and tumbling/mixing the grain.