Water Activity Measurement, Moisture Meter, Measurement and Monitoring of AW Value

The measurement of water activity or equilibrium relative humidity (ERH) is a key parameter in the quality control of moisture sensitive products or materials. If too much water is available in a product, there is a risk of microbial growth and water migration. Our aw measuring devices are very well suited for water activity measurement in various regulated applications and have a wide range of uses: they are used for water activity analysis in the production or storage of pharmaceutical products, for example. Our aw products are also used for measurement in the food sector, where fast and precise measurement results are a decisive advantage.


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If there is too much water in a product, there is a risk of microbial growth and water migration. This can lead to clumping, changes in consistency and reduced shelf-life. Manufacturers of foods and pharmaceutical products must, for example, show to the FDA that the water activity of a product has declined to such an extent that bacteria can no longer grow.

All forms of life depend on water. Water activity indicates the amount of water which is biologically available to microorganisms. It also affects a product’s texture, taste, colour, nutritional value and shelf life. Each species of microorganism (bacteria, yeast, mold…) has a minimum water activity value below which growth is no longer possible.

The measurement of the ‘free’ or available water in any product affects product quality and shelf-life. This is particularly crucial in the pharmaceutical, food and cosmetics industries which are highly regulated. If there is too much water in a product, there is a risk of microbial growth and water migration. This can lead to clumping, changes in consistency or taste, diminution of nutrients or effect product value, as well as reduced storage and shelf-life.

Measuring water activity makes it possible to monitor, control and optimize manufacturing and preservation processes ensuring physical, chemical and microbiological stability of moisture sensitive products.

We offer a wide range of instruments for the measurement of water activity (aw). These include handhelds, the laboratory analyzer HygroLab with four interchangeable probes, a PC-based instrument and the AwTherm with full sample temperature control. Small and large sample holders and liners are available for all product types including expensive medicinal liquids. A significant benefit is that no special product sample preparation is required making Rotronic analyzers easy to use after initial training. Our water activity analyzers can produce accurate and repeatable measurements of aw together with temperature in typically less than five minutes for most product samples, the equilibrium method is also available. Insertion probes can be used for bagged products.

Rotronic water activity probes can be calibrated and adjusted should this ever be necessary.


  • The water activity can be measured using a measuring device or measuring head (e.g. HC2A-AW or AwEasy), which uses a PT100 temperature sensor and a capacitive humidity sensor (WA-1). First, the sample is placed in a sample carrier. A measuring head is then positioned over the sample container (WP-40) to create a microclimate and wait for equilibrium to be reached. The capacitive humidity sensor in the measuring head measures the relative humidity in the microclimate of the sample container. The temperature and relative humidity data are used to calculate the water activity of the sample. The result is shown on the display of the measuring device (e.g. HygroLab), which then generates a report.

  • The water activity (aw) is a unit that denotes non-chemically bound or free water in a substance. It indicates the relative humidity of the vapor phase of a sample. The water activity ranges between 0 and 1, where 0 stands for no available water and 1 for pure water. It influences stability, microbial growth and chemical reactions in food and other materials. Controlling water activity is essential for maintaining product quality, safety and shelf life.

  • Typical applications of water activity measurement include quality control in various industries such as food, pharmaceuticals, cosmetics and materials science. In the food industry, for example, water activity is measured to determine the shelf life of products and to control the growth of microorganisms, which helps to ensure food safety.

  • The results of a water activity measurement are interpreted on a scale from 0 to 1 aw, where 0 aw stands for no available water and 1 aw for pure water. A value close to 0 aw indicates that the product is dry and little or no water is available for microbial growth. Products with a water activity below 0.6 aw are generally stable and have a low susceptibility to microbial growth. Water activity values between 0.6 aw and 0.85 aw provide optimal conditions for the growth of yeasts, molds and some types of bacteria. Products with values above 0.85 aw are susceptible to the growth of pathogenic microorganisms such as salmonella and can pose a risk to food safety.

  • Rotronic water activity meters are the first choice for anyone who needs an accurate measurement of water activity. Our devices feature high-precision capacitive sensors that ensure reliable and consistent results. In addition, Rotronic offers competitive prices that make our devices accessible to a wide range of users without compromising on quality. Furthermore, our extensive product range covers almost every application and offers customized solutions for various industries. Whether in food production, pharmaceuticals or materials research, Rotronic offers the ideal combination of affordability, accuracy and versatility for measuring water activity.

  • Measuring water activity is of crucial importance, especially for quality control in the food and pharmaceutical industries. It enables the evaluation of the microbial stability and shelf life of products. By controlling water activity, companies can prevent the growth of microorganisms such as bacteria, yeasts and molds, which helps to prevent product spoilage and maintain product safety.

  • To carry out your own water activity measurements, you can use a HygroLab as a display unit with a HC2A-AW water activity measuring head, for example. First place the sample in the sample container with the WP-40 sample holder with a PS-40 disposable container to avoid cross-contamination. Then place the HC2A-AW measuring head on the WP-40 sample holder and seal the whole unit to create a microclimate in the sample holder that enables the measurement of water activity. This airtight space enables accurate measurements as no external influences can affect the results.

  • The various methods for measuring water activity have their own advantages and disadvantages. With Rotronic's traditional water activity measurements, which involve waiting for equilibrium, the advantage lies in their ability to deliver accurate and reliable results by capturing the actual moisture equilibrium in the sample. This allows for precise assessment of microbial stability and product shelf life. However, this process can up to almost a hour depending on the sample and environment, resulting in longer measurement times. In contrast, Rotronic's AwQuick measurement offers the advantage of a rapid measurement within 5 minutes. This enables quicker analysis of samples and faster decision-making regarding product quality and safety. However, the drawback of this method is that it uses a mathematical approximation to predict the final water activity without waiting for the actual equilibrium. This may lead to slight deviations from actual values, especially with samples exhibiting complex moisture profiles.

  • The accuracy of water activity measurements can be influenced by various factors. These include the stability of room temperature during the measurement, as temperature fluctuations can affect the measurement results. The presence of outside air in the microclimate surrounding the sample can also lead to inaccurate measurements, as it can alter the moisture distribution within the sample. The quality and cleanliness of the sample chamber or measurement container are important, as impurities or residues can affect the measurements. Calibration and maintenance of the measuring device also play a crucial role in the accuracy of the measurements.

  • Water activity measurements are vital in the development of new food products. They aid in enhancing the shelf life and stability of products by controlling microbial growth. By measuring water activity, food manufacturers can precisely monitor and regulate the moisture content of their products to ensure they meet desired quality standards. This is particularly crucial in the development of dry foods such as snacks, baked goods, and dried fruits, where low moisture content is essential for prolonged shelf life. Moreover, water activity measurements can help optimize the texture, flavor, and sensory attributes of foods by influencing moisture distribution within the product.

  • Yes, water activity measurements can be used for the validation and monitoring of food preservation processes. By monitoring water activity during the preservation process, manufacturers can ensure that the desired microbiological safety standards are met. Adequate preservation aims to inhibit or slow down the growth of microorganisms such as bacteria, molds, and yeasts to ensure the shelf life and safety of the food product.

  • Water activity measurements can be utilized to predict product stability and spoilage by providing insights into the environment where microorganisms can thrive. A low water content (low water activity) inhibits the growth of microorganisms, thus slowing down food spoilage. Therefore, water activity measurements can be used to determine if a product is susceptible to microbial spoilage.

  • Rotronic water activity measurement devices are known for their user-friendly design, specifically engineered for easy handling. Samples are placed in dedicated probe chambers, with the measurement head positioned on top to create a microclimate conducive to measurements. Subsequently, the samples are inserted into the device, which precisely measures water activity within minutes. With intuitive operation and automated processes, Rotronic water activity measurement devices allow for efficient and reliable measurements without extensive training or complicated preparations. This makes them an ideal solution for laboratory and industrial applications requiring quick and accurate water activity measurements.

  • Water activity significantly affects the shelf life and safety of food products. Low water activity inhibits microbial growth and enzymatic activity, thereby extending shelf life and enhancing safety by reducing the survival of pathogenic microorganisms. Conversely, foods with high water activity are more susceptible to microbial spoilage, shortening their shelf life and potentially posing health risks.

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