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How to Autoclave Agar Plates and Reduce Single-Use Lab Plastics

culture media sterilization

Given the quickening pace of global climate change, an increasing number of lab managers are looking for single-use plastics alternatives (and it’s about time!). Making the transition to glass agar plates is an excellent opportunity. Using your existing research autoclave and a supply of pyrex media plates, any lab can substantially reduce its negative environmental impact.

Why Autoclave Agar Plates?

Elicia Preston is a research scientist and lab manager in the Genetics department at the University of Pennsylvania Perelman School of Medicine and a big proponent of sustainable lab practices. As she told Labconscious in 2019, “Labs use huge amounts of energy and produce megatons of waste. As a biologist my fascination with the complex beauty of nature coupled with the irony of trampling nature, to better understand it, frustrates me. So I do what I can to lessen this negative impact of our work.”

As an example, she noted that her lab alone consumes hundreds to thousands of single-use plastic plates per month. Producing one pound of polystyrene media plates (i.e., about 36 dishes) takes 11.28 kWh of electricity and 20.54 gals of water. Doing so creates only about 2 ounces of solid solid waste, but emits two-and-a-half pounds of CO2. And bear in mind that we’re just talking about the resources consumed and waste produced when manufacturing media plates. There’s then the additional energy and CO2 required to ship the plates overseas and then later dispose of them.  

Preston notes that her university purchases more than ~400,000 disposable agar plates and petri dishes per year from just a single distributor. “This petri dish waste, if lined up, would fill the length of the state of Pennsylvania. In contrast, glass culture dishes are only be manufactured and shipped once, and would only enter landfills when broken.”

Preston discusses her approach to sustainable labs and glass media plates here: 

How to Autoclave Agar Plates in your Lab

Ready to start the shift to reusable glass agar/media plates? Here’s a proven workflow for sterilizing glass plates:

  1. Collect your glass plates in separate bins in your red bag waste area; once you have a full load of dishes, proceed to step #2
  2. Dump/scrape the plates (this refuse should be processed as red bag waste)
  3. Soak plates overnight in 5% bleach solution
  4. Use a scrubby sponge to wipe off any writing
  5. Sort your plates and rinse them off (it’s bad to expose the autoclave chamber to bleach)
  6. Load them into a perforated autoclave tray, being sure to leave space for good steam flow (using an autoclave pouch rack can help ensure that the steam contacts every surface) DO NOT WRAP THEM IN FOIL!
  7. Autoclave them for 30 minutes at 121ºC 
  8. Reuse!

“It may seem like a lot of work,” Preston notes, “but it’s really not that bad. You just integrate it in [to your week and workflow] while you’re waiting for an incubation or a centrifuge [step]. It’s a good break when you need to not think so hard for a change.”