top of page

How to Make Grain Spawn Jars

If you're a mushroom enthusiast like me, you've probably considered making your own grain spawn. The first step in this exciting journey is crafting grain jar lids. These specialized lids are equipped with filters that allow the mushroom mycelium to breathe while keeping contaminants at bay, ensuring your fungi thrive.

Image featuring a pair of sterilized grain jars, ready for inoculation in the process of mushroom cultivation.
A couple of sterilized grain jars

In this comprehensive guide, we'll delve into:

1. Understanding grain spawn jars

2. The art of spawn jar lid design

3. The process of creating your grain spawn jars

Mycelium: The Foundation of Mushroom Growth

Before we begin, it’s important to address why we need a modified mason jar lid. As mushroom farmers we’re trying to grow mycelium. Mycelium is the vegetative part of a fungus, consisting of a network of fine white filaments (hyphae). It's essentially the root system of your mushrooms.

Just as plants need healthy roots to grow and thrive, mushrooms need robust mycelium. This mycelium serves as the foundation for mushroom growth, absorbing nutrients from the grain in your spawn jars and using them to grow and eventually produce mushrooms.

Image depicting mycelium, appearing as white, thread-like structures, actively growing and colonizing on a substrate of coffee grounds.
Mycelium growing on coffee grounds.

We must create a contamination free environment for our mycelium to grow and thrive. That’s why we will sterilized grain jars after we’ve created our airport lids.

Understanding Grain Spawn Jars

Grain spawn jars, also known as spawn jars, are integral to mushroom cultivation. They serve as the nurturing ground where the mycelium, the vegetative part of a fungus, grows before being transferred to a fruiting substrate. These jars are filled with sterilized grain, providing a rich food source for the mycelium.

A variety of grains can be used in spawn jars, including rye, wheat, millet, and corn. Rye grain is often a popular choice due to its nutrient-rich profile and the ease with which mycelium colonizes it. However, the choice of grain can depend on the specific mushroom species being cultivated, as some may have a preference for one grain over another. At Happy Little Fungi, we have a particular fondness for whole oats due to their resistance to contamination.

The process of using spawn jars begins with sterilizing the grain, typically through pressure cooking, to eliminate any potential contaminants. Once cooled, the grain is inoculated with a spore syringe or a piece of colonized mycelium. The jar is then sealed with a specially designed lid that facilitates gas exchange while preventing contamination. Over time, the mycelium colonizes the grain, readying it for transfer to a fruiting substrate.