News > Moisture and Water Activity: Why Controlling These Parameters Is Essential for Shelf Life

In drying processes, such as spray drying or fluidized bed drying, achieving the right moisture content is not just a matter of yield. It directly impacts the stability, microbiological safety, and shelf life of the final product.

In addition to total moisture, another crucial parameter is water activity (aw) — a factor still often overlooked by many formulators and product developers.

In this article, we explain the difference between these two concepts and how proper control ensures a longer shelf life and safer, more effective products.

 

💧 WHAT IS MOISTURE AND WHAT IS WATER ACTIVITY?

• Moisture content: the total amount of water present in the product (free + bound). Expressed as a percentage.

• Water activity (aw): the fraction of free water available for chemical reactions and microbial growth. Ranges from 0 (dry product) to 1 (pure water).

A product can have low moisture but high aw — for example, an emulsion or gel. That’s why monitoring only moisture content doesn’t always guarantee stability.

 

WHY ARE THESE PARAMETERS CRITICAL?
🔹 Microbiological safety
Microorganisms such as bacteria, fungi, and yeasts require a minimum water activity level to grow. Below certain aw values, their development is inhibited — preventing contamination and extending shelf life.

🔹 Physicochemical stability
High levels of free water promote degradation reactions like hydrolysis, oxidation, or non-enzymatic browning (Maillard reaction).

🔹 Handling and flowability
Products with inadequate moisture content tend to cake, clump, or absorb moisture from the environment (hygroscopicity), impairing packaging and application.

🔹 Controlled release of actives
In encapsulated products, aw influences the release rate of the active ingredient into the body or formulation.

 

HOW TO CONTROL MOISTURE AND aw DURING DRYING?
✅ Accurate adjustment of inlet and outlet temperatures.
✅ Choosing the ideal drying endpoint: not too wet (instability risk), not too dry (thermal degradation risk).
✅ Use of encapsulating agents that absorb part of the free moisture.
✅ Monitoring aw with specific measuring devices, especially for bioactives, probiotics, or cosmetics.

 

Drying efficiency should not be measured only by speed or yield. To ensure longer shelf life and safer, more stable products, controlling both moisture and water activity is essential.

 

At Labmaq, our equipment allows for fine-tuning of drying parameters and provides support for those looking to optimize product stability, performance, and safety.

Talk to our technical team to discuss your process!