Water activity

Definition

Water activity (a_w) measures the availability of water in a substance for microbial growth. It ranges from 0 (completely dry) to 1 (pure water).

5 Must Know Facts For Your Next Test

1. Water activity is crucial in determining the shelf life and safety of foods.
2. Microorganisms have specific water activity ranges within which they can grow; most bacteria require a higher a_w compared to molds and yeasts.
3. Reducing water activity can inhibit microbial growth, making it a key method in food preservation.
4. A water activity level below 0.6 generally prevents the growth of most microorganisms.
5. Osmotic methods like adding sugar or salt reduce water activity by binding free water.

Review Questions

• What is the significance of water activity in controlling microbial growth?
• How does reducing water activity impact microorganism proliferation?
• What are some common methods used to decrease the water activity in foods?

Related terms

Osmosis: The movement of water across a semipermeable membrane from an area of low solute concentration to high solute concentration.

Desiccation: A method that involves removing moisture from foods to inhibit microbial growth.

Humectant: Substances added to products to absorb moisture and lower the water activity.