The Karl Fischer titration method is specific to water, so it’s a more pure determination of water content, says Dr. Carter in noting its positive attributes. It isn’t impacted by ambient conditions, making it more reproducible. However, this method does require using hazardous solvents that must be handled, stored, and properly disposed of. It’s a complicated process, which requires training and understanding, Dr. Carter says. Furthermore, the equipment is typically more expensive than that for loss on drying. Because no independent standard is possible for moisture content, the measurement is completely empirical—making it impossible to determine accuracy or its true value.
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Explore This IssueFebruary/March 2020
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Near Infrared (NIR) Moisture Meter
NIR moisture meters use calibrations to convert an optical signal into the percent of moisture. They can be quite accurate if regularly calibrated, but users must be aware that as the optics of an instrument age, they change in a way that affects the signal. “NIR instruments are commonly used as inline detectors, but they need to be calibrated to a primary method to maintain accuracy,” Dr. Olmsted says.
On the positive side, Claas says that these meters provide very fast measurements in 30 to 60 seconds, and multi-parameter options (e.g., fat, moisture, proteins). On the negative side, the meter requires calibration; precision and accuracy depend on the quality of calibration. In addition, the meters are expensive.
Since moisture content is subject to many sources of error and doesn’t have an independent standard, it’s impossible to know the true value, Dr. Carter says. Given this, he prefers the loss-on-drying method because it’s the cheapest and easiest to perform. That said, he would not use moisture content to monitor moisture control, but instead would use water activity testing.
Dr. Olmsted prefers a method that’s direct, easy, and rapid. For these requirements, a microwave moisture analyzer with secondary infrared heating is his instrument of choice.
Claas says his choice depends on the application and workplace. For food production in regular operation (e.g., goods-in, in-process control, final quality control) infrared moisture analysis is his choice because it’s versatile and can be used for many different samples (e.g., liquids, creams, powders, granulates), it’s easy to use, results are provided quickly, and it offers great precision and accuracy.
Innovations in Moisture Control
CEM Corp. combines numerous technologies to provide a loss-on-drying analyzer that’s faster than any other primary method on the market—the SMART 6. “Not only does it combine microwave and infrared energy for faster heating, but it also uses active ventilation to both speed the process and to give SMART 6 the capability of operating safely outside a fume hood with no odors being released into the test area,” Dr. Olmsted says. For customers using inline NIR sensors, the SMART 6 offers the ability to calibrate the NIR sensors in only a few minutes, instead of hours with an air oven.
Dr. Carter works with Novasina, a provider of water activity meters, and Neutec Group, Novasina’s distributor for the U.S. market. “Although water activity meters are not new, many food manufacturers are now switching to releasing product solely on water activity values and relegating moisture content to only a measure of purity and standard of identity,” he says. “Some producers have eliminated moisture content testing completely and only measure water activity. By tracking water activity throughout the production process, these producers are able to catch changes in production that may lead to problems before they are widespread.”
In addition, by releasing on water activity, they are able to maximize moisture levels but assure product safety and stability using the water activity. “Since most products are sold on a weight basis, releasing based on water activity makes it possible to maximize profits, eliminate waste, save on energy costs, and release a safe product with optimal shelf life,” Dr. Carter says.
It’s important for food industry organizations to keep their members educated on moisture control methods, and what innovations are happening.