Mixing and Pouring Agar Medium

Creating and pouring agar medium is a crucial step in microbiology and mycology for growing various fungi, including mushrooms. Here's a step-by-step guide on how to mix and create agar medium and then pour it into Petri dishes:

Materials Needed:

• Agar powder (e.g., malt extract agar, potato dextrose agar)
• Distilled water
• Glass container or beaker
• Stirring rod or magnetic stir bar
• pH meter or pH strips
• Weighing scale
• Autoclave or pressure cooker
• Sterile Petri dishes with lids
• Sterilization bags or containers
• Sterilization equipment (pressure cooker or autoclave)
• Sterile gloves
• Sterile work environment (e.g., laminar flow hood or glove box)

Procedure:

Measure Agar Powder:

• Weigh the appropriate amount of agar powder based on your recipe. A common ratio is approximately 20-25 grams of agar powder per liter of distilled water. Adjust based on your specific needs.

Measure Distilled Water:

• Measure the required volume of distilled water, typically 1 liter per batch, in a glass container or beaker.

Mix Agar and Water:

• Slowly sprinkle the agar powder into the distilled water while stirring continuously. This helps prevent clumping. Use a stirring rod or magnetic stir bar for even mixing.

Adjust pH (if necessary):

• Some recipes may require you to adjust the pH of the agar medium. Use a pH meter or pH strips to measure the pH level and make adjustments as needed. Common pH levels for agar medium range between 5.6 and 6.5.

Heat and Sterilize:

• Pour the agar mixture into sterilization bags or containers, leaving some space for steam expansion. Seal them loosely. Place the bags or containers in an autoclave or pressure cooker.

Sterilize:

• Sterilize the agar medium at 15 psi (pounds per square inch) for about 15-20 minutes. The exact time and pressure may vary based on your specific recipe and equipment.

Cool and Solidify:

• After sterilization, carefully remove the agar medium from the autoclave or pressure cooker. Allow it to cool to around 45-50°C (113-122°F). It should remain in liquid form at this temperature.

Pour into Petri Dishes:

• In a sterile environment like a laminar flow hood or glove box, pour the still-liquid agar into sterile petri dishes. Fill the dishes to an appropriate depth, typically around 1/4 inch. Seal the petri dishes immediately to prevent contamination.

Allow to Solidify:

• Let the agar solidify at room temperature. This typically takes about 20-30 minutes.

Store or Use:

• Once solidified, you can store the agar plates in a cool place or a refrigerator until you are ready to use them for microbial or fungal cultures.

 

Creating and pouring agar medium is a precise process that requires sterile conditions and careful attention to measurements and sterilization. Different organisms may have specific requirements, so be sure to follow guidelines appropriate for your application.