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Get to Know Your Grain Jars: A Comprehensive Guide to Safe and Successful Mushroom Cultivation

Updated: Jul 3, 2023

Mushroom cultivation can be an exciting and rewarding hobby. A critical aspect of this process is using the proper grain jars, or bags, to create the optimal environment for mycelium growth.

In this blog post, we will explore the unique characteristics of sterilized grains, the benefits of using them in mushroom cultivation, and how to keep your grains safe from contamination.

Sometimes grains are sterilized in jars and sometimes they are sterilized in polypropylene bags. Whichever you use, the recommendations and characteristics are essentially the same for both. The only difference is that jars are reusable while bags are typically not.

By following the guidelines provided, you will be well on your way to a successful mushroom harvest.

Understanding Your Grains

Grain jars play a vital role in the early stages of mushroom cultivation. They provide a sterilized environment in which fungal spores or liquid cultures can germinate and grow into mycelium.

Let's examine some of the key features of sterilized grains:

Sterilization and Shelf Life of Sterilized Grains

Your grains are 99.99% sterilized through a process called autoclaving, which involves heating the jars at 15 PSIs for 1 hour. This ensures a clean environment for mycelium growth.

However, despite their high level of sterilization, grains typically have a shelf life of 3 months. It is recommended to use your grains within 4 weeks of receiving them to minimize the risk of contamination.

A photo of an All-American Electric Autoclave in operation, set to 15 psi, efficiently sterilizing oats to ensure a contamination-free substrate for mushroom cultivation.
All-American Electric Autoclave

Organic Oats as Grain Substrate

Grains purchased from Happy Little Fungi are filled with 100% organic oats. Occasionally, other materials like birdseed, corn, or other organic matter may be mixed in with the oats, but this is completely normal and will not negatively affect mycelium growth.

Different grains offer unique benefits, and understanding their properties can help you select the best option for your specific mushroom variety. Happy Little Fungi uses oats because they typically have a longer shelf-life than sterilized rye berries and are more environmentally friendly due to simpler processing and are more cost-effective, thus making our grains much more affordable than other sellers.

Here are some other grains that you may encounter online:

  • Rye berries

  • Wheat

  • Wild Bird Seed

  • Barley

Airport Lids for Grain Jars

Grain jars come with airport lids, which are different from regular canning jar lids. These lids are equipped with an injection port and an air filter. The injection port is where you will insert a hypodermic needle to inject spores or liquid culture, while the air filter allows the mycelium to breathe oxygen without letting in contamination. The lids come with aluminum foil on top, which can be removed after injecting spores or liquid culture.

Injection Port and Filter for Grain Bags

Sterilized grain bags offer a convenient alternative to traditional grain jars for mushroom cultivation, providing a spacious and easily manageable environment for mycelium growth. These bags are pre-sterilized, ensuring a clean and contamination-free substrate for your fungi.

Equipped with an injection port and an air filter, sterilized grain bags streamline the inoculation process. The injection port allows for the seamless introduction of spores or liquid culture into the substrate, while the air filter ensures proper gas exchange, enabling the mycelium to breathe without exposing it to contaminants. As a result, sterilized grain bags with an injection port and air filter offer a user-friendly and efficient solution for both novice and experienced mushroom cultivators alike.

An image of a sterilized grain bag featuring a built-in air filter and injection port, designed to provide an optimal environment for mycelium growth in mushroom cultivation.
Sterilized Grain Bag. Includes filter and injection port.

Keeping Your Grains Safe from Contamination

Contamination is one of the biggest challenges in mushroom cultivation, as it can negatively impact mycelium growth and ruin your entire batch. To ensure your grains remain uncontaminated, follow these guidelines:

Never Open the Lids

Avoid opening the lids of your grain jars until you are ready to proceed to step 2. This means waiting until the grains are fully covered in fungal mycelium, as described in the Happy Little Fungi Grow Guide. Opening the lids prematurely can expose the grains to contaminants and jeopardize your entire project.

A close-up view of a fully colonized grain jar, showcasing white mycelium covering the organic oats, indicating it is ready for the next step in mushroom cultivation.
Fully Colonized Grain Jar Ready for Step 2

Store Grain Jars Properly

Store your grain jars in a clean, dry, and cool area, away from direct sunlight or fluctuating temperatures. This will help maintain the sterile environment within the jars and promote optimal mycelium growth.

Practice Good Hygiene

When handling your grain jars, always make sure your hands are clean and wear gloves to minimize the risk of contamination. Additionally, sanitize your workspace and any tools you are using to ensure a clean environment.

Monitor Your Jars

Check your grains once a week for any signs of contamination, such as mold, off-odors, or discoloration. If you notice any signs of contamination, it is best to discard the affected jars and start anew. If you purchased your grains from Happy Little Fungi, contact our customer service to get a replacement!


Understanding your grain jars and taking the necessary precautions to avoid contamination are crucial for successful mushroom cultivation. By following the guidelines outlined in this blog post, you will be well-prepared to grow healthy and fruitful mycelium, setting the stage for a bountiful mushroom harvest. Happy growing!


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