How to Make Agar Gel From Powder

Agar gel is used in petri dishes to cultivate bacteria
••• Jupiterimages/Comstock/Getty Images

Agar is a natural gelling agent derived from marine algae. It is resistant to consumption by bacteria, making it ideal as a medium on which to grow bacteria cultures in petri dishes. It is available in several raw forms including tablets and liquid, but preparing agar powder for use in petri dishes is straightforward.

    Sterilize the petri dishes, beaker, measuring jug, thermometer and stir rod prior to use. You can do this by immersing in boiling water for a few minutes, then allowing to dry on a sterile workspace. You can also sterilize them by wiping with alcohol.

    Measure 500 ml of water into the beaker, followed by the agar powder. The amount of agar powder required per 500 ml can vary depending on the supplier, so check the packaging for instructions on how much powder to add -- 10 to 15 grams is the usual range. This will yield sufficient agar gel for 25 petri dishes.

    Place the beaker over a heat source such as a bunsen burner, and stir with the stirring rod as you bring it to a boil. Boil the mixture for 1 minute.

    Place the thermometer in the beaker, and allow the mixture to cool to between 45 and 50 degrees Celsius.

    Pour 1/4 inch of liquid into each sterile petri dish, making sure to replace the cover immediately. The agar will form a stiff gel at room temperature, and the petri dishes will be ready for use.

    Things You'll Need

    • Petri dishes
    • Laboratory beaker, 1000 ml
    • Agar powder
    • Cooled boiled water or distilled water, 500 ml
    • Measuring jug
    • Bunsen burner or other heat source
    • Glass stirring rod
    • Heat-resistant gloves
    • Laboratory thermometer

Related Articles

How to Make Biogas
How to Check Algae Using a Spectrophotometer
How to Make Agar Plates
How to Make a 1% Sucrose Solution
How to Check Algae Using a Spectrophotometer
What Are Agar Slants?
How to Make Mushroom Spawn
How to Grow Bacteria in Agar
How Is a Pure Culture Prepared Directly?
How to Make Nutrient Agar at Home
Uses of Alum Crystals
How to Make Your Own Agar for Petri Dishes
Types of Agar Plates
Five Steps to Prepare Agar Slants
How to Calculate Solubilities
How to Measure Bacterial Growth in Petri Dishes
How to Make Liquid Calcium Chloride
How to Grow Penicillin for a Science Project
How to Use Propylene Glycol