How to Sterilize Agar With an Oven

Agar is often used as a vegetarian substitute for traditional gelatin.

Agar is a substance processed from certain species of red algae. It has many culinary uses, such as a gelatin substitute and dessert thickener. It is also used in scientific pursuits as a medium for cultures. Agar must be sterilized prior to laboratory use to prevent contamination of a culture. While this is normally done with a hot plate or autoclave, it is possible to use an oven to boil agar to sufficiently sterilize it for immediate use.

Things You'll Need

• Stove-top oven
• Glass beaker
• Stirring rod
• Flat-bottomed pot
• Aluminum foil
• Heat-resistant gloves
• Petri dishes

Instructions

1. Put on heat-resistant gloves. Loosen the cap of the agar storage container and put it in a bath of boiling water. Heat it until the agar melts at 185 degrees Fahrenheit. Open the bottle and run a flame over the open end to sterilize it.

2. Fill a beaker halfway with the melted agar. Stir the melted agar thoroughly with a stirring rod. Cover the top of the beaker with non-adhesive aluminum foil to contain vapors without completely sealing the beaker. Place the beaker in a flat-bottomed pot and place the pot on a stove-top burner.

3. Raise the burner temperature slowly while carefully monitoring the agar. It is crucial to take this step slowly, as agar does not have a fixed boiling point and visual inspection is necessary to prevent the agar from boiling over. Set the temperature to the lowest possible setting that maintains boiling and allow the agar to simmer for thirty minutes.

4. Allow the agar to cool to 122 degrees Fahrenheit. Pour the agar into sterilized petri dishes, filling them with approximately 1/8-inch agar. Seal the petri dishes and use them within one to two days.

Tips & Warnings

• Agar can be sterilized inside an oven by placing the beaker on a flat cooking sheet, but this method is less accurate. It more difficult to reduce an oven's internal temperature than a burner's, and this method carries a greater risk of spill-over.

• Do not use a microwave to melt or boil agar, as this may lead to the substance splashing violently, which will cause a considerable mess and possible injury.

• Move the boiled agar with care, as sudden movement can cause it to boil over the edge of the beaker.

References

• University of Missouri-St. Louis; Sterilizing Laboratory Materials for the Classroom; Teresa Thiel; 1999

Resources

• Barry Farm Foods: Agar Powder
• Science Buddies: All About Agar