Why is agar used to make solid media for growing microorganisms?

Agar is widely used as a solidifying agent in microbiological culture media because it possesses unique physical and chemical properties that make it superior to alternatives like gelatin.12

Key reasons for its use include:

• Thermal Stability: Agar dissolves in boiling water but remains liquid until it cools to approximately 37 °C (99 °F), at which point it solidifies into a firm gel. Unlike gelatin, which melts at 37 °C, agar remains solid at the typical incubation temperatures required for many bacteria.31
• Resistance to Degradation: A primary advantage of agar is its resistance to microbial degradation; most microorganisms cannot break down the polysaccharide structure of agar, ensuring the medium remains solid throughout the growth process.2

Extracted from red algae, this seaweed product provides a stable, reliable surface that allows scientists to isolate and observe individual microbial colonies.32