When do you stop drying, that is the question? We make this determination easy and objective by including a simple hygrometer with your DEHYTRAYTM that can be used to determine the water activity (aw) of your product. The water activity of a product is a measure of the potential for mold, bacteria and yeast to grow on the product by utilizing the product’s free unbound water, and is an indication of whether the product is dry enough for storage. The free unbound water from the product that comes into equilibrium with the air pockets between the product in a closed environment like a sealed air-tight bag is known as the Equilibrium Relative Humidity (ERH). The aw is the decimal of the ERH. Low water activity is better than high water activity.
A product that has a water activity below 0.65 or 65% equilibrium relative humidity is sufficiently dry for safe storage and will not support the growth of storage molds. Note that the water activity is not the same as the moisture content of a product. Hence, two different products might have the same water activity, but different product moisture content. The simple hygrometer method for measuring the aw or ERH developed by Dr. Woloshuk and his team at Purdue University in Indiana, can be used to objectively determine when to stop drying. This will enable you to maintain premium and uniform product quality from batch to batch, and ensure that you have safely dried your product for long-term storage in order to guarantee shelf life stability.