Nutrition & Food
Advanced

Water Activity

Ratio of a food's vapour pressure to pure water — governs microbial spoilage.

Formula

aw=pp0a_w = \frac{p}{p_0}

Variables

pVapour pressure of food
p_0Vapour pressure of pure water

Example

Dried fruit ≈ 0.6

Did You Know?

Most bacteria stop growing below a water activity of 0.91, which is why salting, drying and sugaring preserve food.

water activitypreservationshelf life