Which water activity threshold is associated with microbial growth risk?

Which water activity threshold is associated with microbial growth risk?

• A. Less than 0.6
• B. Greater than 0.85
• C. Equal to 0.95
• D. Greater than 0.99

Answer: (B)

Water activity shows how much free water is available for microorganisms to use. It ranges from 0 (no free water) to 1.0 (pure water). As aw increases, microbes have more water to support metabolism and growth. A practical threshold used in many safety contexts is around 0.85; above this level, the majority of microbes can begin to grow, so the risk of microbial growth rises. Below about 0.85, osmotic stress from solutes makes growth much harder for most organisms. Therefore, the threshold associated with microbial growth risk is greater than 0.85. The other values imply drier or more water-rich conditions, but 0.85 is the commonly cited point where growth risk becomes significant.

Water activity shows how much free water is available for microorganisms to use. It ranges from 0 (no free water) to 1.0 (pure water). As aw increases, microbes have more water to support metabolism and growth. A practical threshold used in many safety contexts is around 0.85; above this level, the majority of microbes can begin to grow, so the risk of microbial growth rises. Below about 0.85, osmotic stress from solutes makes growth much harder for most organisms. Therefore, the threshold associated with microbial growth risk is greater than 0.85. The other values imply drier or more water-rich conditions, but 0.85 is the commonly cited point where growth risk becomes significant.