agar plates?

Question

When making agar plates, why do you have to wait until the liquid agar cools to 50 degrees before pouring into the petri dish?

Answer 1

Mainly because the thin plastic melts or warps at high temperatures. 60 is probably safe, but 50 is definitely safe. Also, if you're going to add a selective antibiotic to the agar, you want to keep in mind that most of them crap out at temperatures greater than about 60C. Better to cool the agar solution, add in the ampicillin (or whatever) and then pour.