Agar petri dishes are crucial to science experiments that involve growing bacteria or other microorganisms. The agar serves as a food for the bacteria, which is why it is often called nutrient agar. Although prepared petri dishes can be purchased, many students and labs make their own agar petri dishes using bottled agar or a powdered agar mix.
- Skill level:
Things you need
- Sterile petri dishes with covers
- Bottled or powdered agar
- Hot water
- Measuring cup
Loosen the cap of the bottle of agar to allow it to vent.
Warm the bottle in a bowl of hot water until the solid agar melts into a liquid.
Pick up the bottle carefully, using potholders if it is hot to the touch.
Preparing Bottled Agar
Read the instructions on the agar packaging to find the correct ratio of agar powder to water.
Pour the correct amount of boiling water into a sterile measuring cup, ideally one with a spout for pouring.
Mix the agar into the water, using a sterile tool, until it is fully incorporated.
Preparing Powdered Agar
Set your sterile petri dishes on a flat surface, such as a countertop or lab bench. Keep the lids on the petri dishes until you are ready to pour.
Pick up the petri dish lid with one hand and move it to the side, just enough to make a small opening in the petri dish.
Use your other hand to pour the liquid agar into the petri dish, covering the bottom with about 1/8 inch of agar.
Replace the lid on top of the petri dish before moving on to the next dish.
Let the petri dishes sit on the counter until the agar has solidified.
Turn the petri dishes upside down and put them into a refrigerator.
Tips and warnings
- If you would prefer not to use boiling water, both bottled and powdered agar can be heated in the microwave instead.
- All materials used in the preparation of agar petri dishes should be sterile to avoid bacterial contamination.
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