In microbiology, media is allowed to cool to around 45°C before pouring plates to prevent condensation and maintain the viability of any added supplements.
If the media is too hot when poured, it can cause excessive condensation on the Petri dish lid as it cools. This moisture can drip onto the agar surface, potentially spreading bacteria or other organisms across the plate and disrupting isolated colony formation.
Some media require the addition of heat-sensitive supplements (e.g., antibiotics) to support the growth of specific organisms. If the media is too hot, these supplements may degrade, reducing their effectiveness and potentially affecting the growth conditions.
At 45°C, the agar cools at a rate that allows for uniform solidification, creating a flat, smooth surface ideal for streaking or spreading microorganisms.