Step-by-step guide for preparing agar media for petri dishes:
- Agar powder
- Malt Extract powder, Syrup Malts or Potato Dextrose
- Distilled or deionized water
- Digital scale
- Measuring cup
- Autoclave or pressure cooker/ canner
- Heat-resistant containers (such as Media Bottles or Erlenmeyer flasks)
- Stir bar & Magnetic Stirrer
- Sterile petri dishes
- Disposable Gloves
- 70% Isopropyl Alcohol
- Weigh out the desired amount of agar powder according to the manufacturer’s instructions. A common ratio is 20-30 grams of agar per liter of water. We prefer more firm agar, so 30 grams is our go to.
- Add the agar powder to the heat-resistant container through a funnel.
- Add in 20-30 grams of your desired carbohydrate. Malts and Potato Dextrose will both provide essential minerals and carbohydrates for luxurious growth of Higher fungi. Please note that too much Carb can be toxic to fungi and too little will leave your mycelium starved for nutrition.
- Add distilled or tap water to the container. The amount of water added will depend on the desired concentration of agar and the size of the container.
- Place a stir bar or glass rod in the container to aid in mixing.
- Heat the mixture to boiling while stirring until the agar is completely dissolved.
- Adjust the pH of the mixture to the desired range using a pH meter or pH strips. For most agar media, a pH of 5.5 to 7.0 is suitable. Although PH can make a difference in quality of growth this is not necessary for good growth and success. If you have low PH water then distilled water is recommended and checking PH would be necessary.
- Sterilize the agar mixture by autoclaving or pressure cooking according to the manufacturer’s instructions. This typically involves heating the mixture to 250f for 20-30 minutes @15 PSI
- Allow the agar mixture to cool to around 120-140f. This temperature is suitable for pouring into petri dishes. If your media is too hot to handle let cool an additional 5-10 degrees.
- Before you pour your media, it is essential to sterilize your work space with 70% isopropyl alcohol. Clean your table, still air box(if applicable), your sleeves of petri dishes, and hands well. This will limit the probability of contaminants.
- Pour the agar into sterile petri dishes to a depth of 4-5 mm. Roughly 20ml of media per 90mm petri dish. Or half full.
- Allow the agar to cool and solidify before use. If you are working in a still air box it is essential to work as clean as possible.
- Store the petri dishes in a cool, dry place until needed.
Note: 1000ml media bottles will usually fill 50 90mm petri dishes. It is important to work in a sterile environment when preparing agar media to prevent contamination of the media. This includes using sterile containers, tools, and working in a laminar flow hood or other sterile environment.