What is Agar?

Agar is a crucial medium for growing and studying fungi, especially mushrooms, in mycology. It provides the perfect environment for spores to germinate and for mycelium to spread. Whether you’re a beginner or an experienced cultivator, making your own agar plates at home can save money and give you more control over the process. In this post, we’ll walk you through everything you need to know about creating agar for mycology.

Agar is a gelatinous substance derived from seaweed, often used as a medium for growing cultures in laboratories. For mycology, it’s typically combined with nutrients that support the growth of fungal cultures. The most common types of agar used in mycology are Light Malt Extract Agar (LMEA), Malt Extract Agar (MEA), Potato Dextrose Agar (PDA), and Sabouraud Dextrose Agar (SDA).

For this tutorial we will be making Light Malt Extract Agar (LMEA).

Materials You’ll Need

To make your own agar plates, you’ll need the following materials:

• Agar powder: This is the base of your medium.
• Nutrient source: Light Malt Extract and Nutritional Yeast.
• Distilled water: Avoid using tap water, as it can contain impurities that affect the growth of your cultures.
• Petri dishes: These will hold the agar once it’s prepared.
• Measuring scale: For accurately measuring your ingredients.
• Heat-resistant container: To mix and heat the agar solution. We prefer Medium Bottles.
• Pressure cooker or autoclave: For sterilizing the agar and tools.
• Stirring rod or spoon: To mix the agar solution.
• Alcohol or flame source: For sterilizing tools during the pouring process.
• Aluminum foil: To cover the container so water does not get inside.
• Infrared thermometer gun: To read agar temperature.
• Parafilm tape: To seal the Petri dishes and protect from outside contaminates.

Step-by-Step Instructions

1. Prepare Your Workspace

Before you start, ensure your workspace is clean. Wipe down surfaces with alcohol or a disinfectant to reduce the risk of contamination. Also, sterilize any tools you’ll be using, either by wiping them with alcohol or by using a flame.

2. Measure the Ingredients

The standard recipe for creating agar medium involves the following ratios:

• 10 grams of agar powder
• 10 grams of Light Malt Extract (LME)
• 1 gram of Nutritional yeast
• 500ml of distilled water

Using a precise scale, measure out these ingredients. Adjust the quantities based on how much agar you want to prepare. This recipe makes about 20 plates.

3. Mix the Ingredients

In a heat-resistant container, combine the agar powder and nutrient source with distilled water. Stir the mixture thoroughly to dissolve the ingredients. It’s important to get rid of any clumps to ensure the agar sets evenly.

4. Heat the Mixture

Place your container on a stove or hot plate and bring the mixture to a boil. Stir continuously to prevent the agar from sticking to the bottom. Once the solution reaches a boil, reduce the heat and let it simmer for about 10 minutes. This ensures that the agar and nutrients are fully dissolved and evenly distributed.

5. Sterilize the Agar Solution

Pour the hot agar solution into a sterilizable container, like a glass bottle or a beaker. Ensure that the cap to the container is not sealed tight. Make sure it is loose so that the air is not trapped inside the container while inside the pressure cooker. This would lead to the container breaking due to the pressure build up. After you loosen the caps take a piece of aluminum foil and cover the cap so water does not enter the container.

If you’re using a pressure cooker, place the container inside and cook at 15 psi for 25 minutes. This step is crucial for killing any contaminants that might interfere with your fungal cultures. The following image is the end result.

6. Pour the Agar into Petri Dishes

After sterilization, allow the agar to cool slightly until it’s safe to handle but still liquid. Take the plates out of the sleeve and prepare them in a stack of ten.

Adding the agar to the Petri dishes too early can lead to condensation building up on the lids of the dishes. The agar can also solidify if you decide to let the temperature drop below 120 degrees Fahrenheit. The optimal time to pour the agar is between 120 degrees Fahrenheit and 130 degrees Fahrenheit.

After reaching the optimal temperature, carefully pour the agar into sterile Petri dishes, filling each one to a depth of about 1/4 inch (0.5 cm). Work quickly but carefully to avoid introducing contaminants and ensuring that the agar does not solidify. If possible, perform this step in a laminar flow hood or in a still-air box to minimize exposure to airborne spores.

7. Let the Agar Solidify

Once poured, let the Petri dishes sit undisturbed until the agar solidifies. This usually takes about 30 minutes. If you see any condensation forming on the lids, try to avoid shaking or disturbing the plates, as this can cause excess moisture to drip onto the agar, potentially leading to contamination. Start at the bottom and lift up the lid and then work your way up. After the agar solidifies you can add parafilm tape around the sides of the plates to seal them from outside contaminates. We recommend using two strips per Petri dish and folding it in half horizontally.

8. Store or Use the Agar Plates

If you’re not using the agar plates immediately, store them upside down (lid down) in a cool, dark place. This prevents condensation from dripping onto the agar surface. Properly stored, agar plates can last for several weeks.

Tips for Success

• Avoid contamination: Always work in a clean environment and sterilize your tools thoroughly. Any contaminants in the agar can ruin your cultures.
• Use a still-air box: If you don’t have access to a laminar flow hood, a still-air box can help reduce the risk of contamination when pouring agar.
• Label your plates: If you’re preparing multiple batches or different types of agar, label your Petri dishes with the date and type of agar used.

Conclusion

Creating your own agar plates is a rewarding and cost-effective way to dive deeper into mycology. With a bit of practice, you’ll be able to produce consistent, high-quality agar that will support the growth and study of various fungi. Whether you’re cultivating gourmet mushrooms or exploring the fascinating world of fungi, mastering agar preparation is a fundamental skill that will serve you well in your mycological journey.

Happy cultivating!