Water Activity and Isotherm Testing

Complete moisture analysis

Water Activity and Isotherm Testing

Lab analysis

The testing lab’s secret weapon is an AQUALAB VSA—a patented instrument that can create dynamic dew point isotherm (DDI) curves.

What are isotherms?

An isotherm is a graph that shows how a product’s moisture profile changes as it takes on or loses moisture. Most instruments that create isotherms automatically hold a product sample at a user-specified water activity. They use a microbalance to track tiny changes in weight as the product comes to equilibrium. This creates a static (DVS) isotherm.

The power of DDI curves

The AQUALAB VSA can be used to generate static DVS data, but it also uses the unique AQUALAB chilled mirror dew point sensor to create high-resolution dynamic (DDI) isotherms. The DDI method doesn’t hold the product at a specific water activity. Instead, it passes saturated wet air over the sample while tracking both weight change and water activity. This creates an adsorption curve. Then it passes desiccated air over the sample to create a desorption curve. These DDI curves show how a product’s water activity changes as it absorbs and desorbs moisture with high data resolution, providing details not available from DVS methods.

METER Food Lab offers standard water activity testing to troubleshoot a product or process or to provide a third party result.

The lab also specializes in isotherm testing with the only instrument that can generate high-resolution isotherm curves. Use our DDI capabilities to test your challenging samples and generate the data you need for a complete understanding of the moisture in your product. METER scientists can also help you interpret results and do on-site investigations. Harness the power of water activity to:   

  • Identify phase transition points for your product
  • Predict how moisture will migrate between components
  • Identify your product’s most stable condition (the monolayer value)
  • Predict what will happen to your product when subject to temperature abuse
  • Help you pick packaging
  • and more

Request a quote

Here are some examples of services we offer. You can request just one service or a combination of services.

Your product’s isotherm

Product samples will be analyzed in the AQUALAB VSA to create a product-specific sorption and desorption DDI curve. Static DVS testing can also be performed. The DDI curve gives you a detailed picture of moisture interactions within your product. It’s like ripping the lid off so you can see exactly how formulation, packaging, and storage decisions affect your product. Reporting options include data only, data plus a simple summary, or data plus analysis and consultation.  Isotherm data can be used in mathematical models to determine the following values. If you provide the lab with the necessary information, these analyses can be included in your report:

Ingredient mixing models

Isotherms for multiple ingredients can be combined to predict what will happen if the components are combined at different water activities and experience moisture migration. The final equilibrium water activity and the final moisture contents of each component can be predicted to determine if moisture migration will lead to a failed product.

Effects of temperature abuse

Your report can predict what will happen to your product if stored under abuse conditions. It can identify the temperature sensitivity of your product’s water activity and determine the temperature where the water activity will change enough to lead to product failure.

Critical water activity

DDI curves show where phase changes occur within your product. They can predict where caking and clumping will occur, find glass transition and deliquescence points, and pinpoint critical moisture ranges for product quality.

Packaging evaluation

Your report can include packaging specifications required to achieve a certain shelf life and whether current packaging is excessive or inadequate for your application.

Monolayer value

The monolayer value represents the most stable condition for any product and where it will have its maximum shelf life. In general, the closer the product can be processed to its monolayer, the more stable it will be.