Category Archives: Water Activity

Five Applications where Water Activity is critical and why!

Not clear on what water activity is? Check out our other posts on water activity here!

Water activity affects a wide range of products from pharmaceuticals to foods, here we take a brief look at five typical applications where water activity measurements are used.

Remember water activity affects biological, chemical and physical properties of products.

Application 1 – Food

Water activity is critical in food production, reducing water activity reduces the available moisture for spoilage organisms to utilise as such low Aw can limit or prevent growth and spoilage.

Aw is often used to screen raw ingredients or end products to confirm that they are within tolerance. Aw measurements only take a few minutes and can therefore provide immediate feedback. This can save time, money and prevent health risks or product spoilage.

Aw can be used as an excellent indicator of shelf life. Once a production process has been fine tuned to deliver products with suitable shelf-life, online aw measurements can confirm production consistency.

Classic methods to control Aw in food are listed below.Slide14

Application 2 – Paper

Water activity or %equilibrium relative humidity in paper may not be your first thought, but the impact of poor or changing ERH in paper can be very costly. Changes in ERH can cause paper to curl or lead to increased static both of which can cause paper jams. For an industrial printing company this can lead to costly downtime. ERH also affects the binding of inks, drying times and ultimately spoilage by moulds and fungi.Slide15


Application 3 – Pharmaceutical Products

Drug production and storage is one of the most highly regulated manufacturing sectors. All stages of drug production, storage and delivery rely on critical control of many factors including water activity. Most drugs must be stored in stable conditions hence the advanced moisture impermeable packaging used. Aw readings as well as humidity monitoring and control are utilised to ensure free water is maintained within tolerance.



Application 4 – Seed preservation and storage

Seeds present an interesting challenge, if Aw is too low the seeds quickly become non viable, where as too high and they may germinate or suffer spoilage through mould or fungal growth. One of the most critical seed preservation projects is the Millennium Seed Bank project. More details about how Rotronic AW meters were used is avaialble on the Kew Gardens websiteSlide17


Application 5 – Soaps and powders

Finally we come to good old washing powder, even with powders and liquids now packed into clever tablets and pods Aw remains critical. The materials must be stored in a way that ensures safe delivery to the customer but can be released once in contact with water in your washing machine. The science of behind the latest washing powders and liquids relies heavily on the measurement and conrtol of water activity and %ERH!Slide18


Hopefully this brief in site into how water activity affects so many day to day products has been useful. For more information visit our website or contact us to discuss!

Dr Jeremy Wingate
Rotronic UK

Durable, Adaptable, Accurate


Campbell Scientific (CSC) are an ISO 9001 certified company who are a leading manufacturer in a variety of applications related to weather, water, energy, gas flux and turbulence, infrastructure, and soil. Campbell Scientific, are committed to satisfying the instrumentation needs of their customers, and are internationally recognised in the measurement and control industry for producing accurate and dependable instruments




CSC systems are acclaimed for their dependability, which they demonstrate even in the most extreme weather climates. Their attributes include wide operating ranges, low energy usage, many communications options, and the flexibility to support a wide variety of measurement  and control applications. Applications include, agriculture, air quality, fire warning, water quality, weather and climate recording, structural monitoring, Geo-technical monitoring and mining.

Rotronic and CSC have been business partners for many years, CSC uses the standard Rotronic meteo probe in many applications. Recently CSC installed the probe in a network of Road Weather Information Systems  in Kelowna, British Columbia. CSC selected the probe because of its reliability, ease of use and accuracy. The HC2A-S3 is also highly regarded for its ability to function in extreme temperatures, this makes it good for the  Canadian climate, and a perfect complement to Campbell Scientific systems.

” We value the Rotronic HC2A-S3 probe for its ability to function at extreme temperatures.” Mike Ryder Campbell Scientific, Canada

For more information on the latest HC2A-S click here ,or for any of our products please visit the Rotronic website.

Meteorology Numerical Weather Prediction


The calculation of weather data

What is the weather going to be like tomorrow?

For a long time, people have tried to predict weather conditions using the hydrologic climate cycle.In the early 1920’s scientists were able to compile a six hour forecast, back then it took six weeks to analyse weather data collected at only two points in Europe and calculate, by hand, a useful illustrative model. Today, supercomputers are used to predict the weather for a period of several weeks. The complex modelling programs require several million data points for parameters such as temperature, humidity, pressure, vertical & horizontal wind velocity with time stamps and absolute coordinates. To create a correlation between the data and the environment, scientists “slice” the atmosphere virtually into smaller horizontal &vertical parts—this process is called discretisation. It is more useful to compute the chronological change of the parameters using this model.

watercycle-pageClockwise from top left: Map of the average temperature over 30 years. .Weather station on Mount Vesuvius. .Water cycle summary

Meteorological events that are too “small” such as a single thunderhead, layer clouds or smaller turbulence’s will be parameterised through variables. This parameterisation is a science of its own that aims to reduce uncertainties as best as possible. Every forecast calculation starts with the current weather conditions. The quality of this input is crucial for the accuracy of the final forecast. Meteorologists link the forecast of yesterday’s weather with the actual measured parameters. Only large data centres are capable of computing this data assimilation. The overall result is a best possible calculation basis predict the weather for the next day. If this groundwork is flawed the forecast may be incorrect. For example, it could report rain at the wrong location. Today’s meteorological mathematicians also take parameters into account that change extremely slowly compared to the other factors. Growth and the reduction of polar ice, or the temperature of the oceans are summarised as boundary values. After a model is run using all the available data, meteorologists process and customise reports for a wide range of target groups such as public authorities, flight control centres, energy producers, industries and many more. These reports also include specific weather warnings.

Why the need to measure humidity?

Atmosphere_composition_diagramAtmosphere composition diagram

As described above, the daily weather forecast relies on the precise measurement of weather parameters. The science of numerical weather prediction aims to describe the daily hydrologic cycle in numbers. Humidity plays an  important role. Typically, data errors will multiply during calculations. Humidity values influence weather calculations e.g. through the water vapour balance equation— this formula expresses the influence of humidity through rain & condensation, and vice versa. Incorrect measurement or incomplete humidity data directly leads to wrong predictions of a huge number of weather phenomena such as the condensation altitude of clouds, locations of hyetal regions, fog layers and storms. In 1999, incorrect data sent by a weather station in Nova Scotia, Canada led to a incorrect forecast for Hurricane Lothar two days before it hit Central Europe. Authorities were insufficiently prepared to alert people in time. The prediction of rain and snowfall is still challenging for meteorologists. Only more extensive networks of weather stations and enhanced mathematical models will reduce problems due to unknown factors.

Facts & Figures

  • 7 inches is the diameter of the largest hailstone ever recorded.
  • Sukkur City in Pakistan is one of the most humid places in the world with
    30 °C dew point & a felt air temperature of 65 °C.
  • A study showed that a small thunderstorm system holds more than 10 million tons of water.
  • No two weather patterns are completely alike.
  • Some weather models assimilate data obtained from more than 25,000 weather stations.

Rotronic International Sales Meeting 2014 Grindelwald Photo Gallery

Great to see everyone at the 2014 ISM in Grindelwald!

Water Activity and Moisture Content… What is the difference?

Water Activity and Moisture Content are two very different parameters which are often confused and misused.

In a meeting today with a manufacturer of coffee capsules and pods, these differences were critical.

– Their  whole bean supplier provided each batch with  moisture content readings.

– However customers buying the coffee capsules and pods were asking for detailed water activity measurements for each batch. In addition for BRC Food Safety and shelf life validation of the final product, water activity was required.

Why are there these differences and can one measurement be used to determine both values?

Moisture content is probably the simplest value to understand.  It is simply the quantity of water contained in a material. Traditionally measured through loss of weight on drying. This method raises some issues, depending on the drying temperature you may not remove all water or may also remove other non water compounds.

More modern methods resolve these issues and use infra red absorption. This way the water content is directly measured, the method is non-destructive and far quicker. 

Moisture content is typically given as a percentage in terms of weight.

Infrared Moisture Measurement
Infrared Moisture Measurement – A measure of moisture content through IR adsorption


Water Activity (aW) is a measure of the free water in a sample, and ranges between 0…1.  Pure water would have an aW of 1.0. As water activity measures the ‘free’ or ‘active’ water in a sample it is more relevant to growth of organisms, chemical processes, enzyme activity and physical parameters like size and clumping as these are only effected by the water that can be chemically interacted with. Interestingly Water Activity is related to Moisture Content but it is product and temperature specific.

aW… is more relevant to growth of organisms, chemical processes, enzyme activity and physical parameters

Rotronic HygroLab
Rotronic HygroLab Water Activity Measurement – A measure of the ‘free’ water

What is free water? Water can be bound in materials in two broad ways.

1. Chemically Bound Water. Is bound so tightly that it cannot be utilised by bacteria, enzymes etc. It can be removed  through high temperature heating.

2. Free Water. Is bound through weak bonds, structural diffusion, capillary condensation and surface binding. It can be utilised by bacteria and can exchange with the environment, it is also removed through heating.

For instance a whole grape would have the same moisture content as two halves of the same grape. However the aW would be far lower in a whole grape as much of the water is bound inside the grape skin and only made free when the grape is cut in half!

Take a look at our Water Activity white paper or our Knowledge base for more information.

Introduction to Water Activity

Water Activity White Paper and Product Overview

Application note F004 – Water activity in the food industry