Guidelines for the measurement of water
activity and ERH in foods

Understand the importance of water activity in food preservation and adopt procedures to ensure it is measured accurately and reliably

Water activity (or relative equilibrium humidity as it is often also known) is an important component of many food preservation systems. It has an impact on both product safety and product quality. Accurate determination of water activity is therefore crucial in assuring safe production of high quality foods. This guide sets out to explain the concept of water activity and its importance in food preservation, and to describe the principles of the techniques used to measure water activity of foods. More specifically, sections deal with:

• How water activity affects microbial growth and thus contributes to food safety and quality
• The principles on which the different instruments available operate
• Pitfalls to avoid when preparing samples and measuring water activity
• Guidance on approaching instrument maintenance and calibration
• Special considerations for different food types including composite, coated and multi-layer products

Who should use this guide?

The guide is aimed both at food industry technical personnel involved in measuring water activity and, more generally, at others who need to understand the basic concept of water activity and its relevance to food preservation, such as product developers, production managers and quality management personnel.

It was written and reviewed by experts drawn from food manufacturers, retailers, instrument manufacturers and technical organisations including CCFRA. It provides authoritative guidance relevant to current practices and a diversity of food products, and is designed to ensure its practical usefulness to companies across the food industry.

Contents

Introduction - the concept of water activity and its measurement

Introduction and historical background
Definitions
Water activity and bacterial growth
Water activity and product quality
Water activity and other preservation factors
Principle uses of water activity data

Methods of sampling and sample preparation

Introduction
Detailed considerations
Developmental and routine measurements
Packaging films

Principles and methodology of water activity measuring devices

Overview
Effects of temperature
Uncertainty of measurements
Commonly used measurement techniques
Instrument configurations
Maintenance and calibration of instruments

Microbiological interpretation of water activity measurements

Introduction
Factors that interact with water activity
Problem products
Effects of water activity on different micro-organisms

Suppliers of equipment

References

Glossary of terms

Softcover - 46 pages