Speed up testing, and reduce variability by creating simple, consistent SOPs for preparing and testing your samples. Here are 6 best practices to consider as you develop your own procedures.
Keep it representative
Always test products in their final state. If the product isn’t chopped, ground, or sliced before it reaches consumers, avoid doing this to the product before measuring its water activity. Some slicing or cutting may be necessary for the sample to fit inside the sample cup, but keep this to a minimum.
When measuring multicomponent foods, place a representative amount of each component into the sample cup. If measuring a product such as filling sandwiched between two cookies, put both parts (cookie and filling) into the sample cup.
Perform different preparation tests on samples, and measure the change in water activity that results. Use this data to determine the method which produces the most stable results.
Eliminate unnecessary steps
Use testing data as a guideline to determine what kind of preparation procedure is right for each product. Eliminate any unnecessary steps.
Once you’ve determined the best method, establish a sampling procedure with set guidelines. For example, specify how many seconds the samples should be crushed, how they should be handled, and the temperature at which measurements should be made.
Keep it covered
Exposed products with a water activity higher than room humidity will lose moisture, and those with a water activity below room humidity will gain moisture. To avoid moisture gain or loss, minimize exposure time. Sample lids are excellent for this purpose. For storage beyond an hour, parafilm the lids on, or store samples in hermetically sealed containers.
Keep it clean
Place the instrument in a clean location. Wash your hands, or wear lab gloves. Wipe the bottom, the edges, and the rim of the sample cup with KIMWIPES® tissues before setting it into the chamber. This prevents contaminants from spreading into the chamber. Fill the sample cup only half full.
Types of products that may need special consideration
The following products may need special sampling practices in order to obtain an accurate reading.
Products with a moisture barrier
Products that have a coating, like chocolate-covered nuts or coated candies, may be slow to come to equilibrium. They can be cut or crushed to expose interior, but do not grind. Grinding causes moisture loss and is rarely necessary.
Products high in fat
In fatty meat products, oils, or fatty desserts, the oils and fats become a moisture barrier, and samples are slow to emit moisture. Quick water activity testing methods will give inaccurate results. These samples must equilibrate in the chamber for a longer period of time. You can also use low-emitting mode for faster readings. Please contact support for more information.
Products with extremely low water activity
These products may be slow to come to equilibrium, so expect longer read times.
Multiple component products
Cakes with filling, cheese and crackers, or cereal with fruit are all multiple component products. For an accurate reading, one option is to check components individually. You can also use a representative sample if you are able to keep the ratio of the components right. Watch for moisture migration, and test larger products in several places to avoid microbial growth hotspots.
Insider sample prep strategies for faster, more accurate readings
Support expert Wendy Ortman has visited hundreds of customers to help them get the best possible speed and accuracy from their water activity measurements. In this webinar, she shares what she’s learned about sample prep, including:
- Why temperature differences matter, and what you can do to minimize them
- How to handle products that absorb/desorb moisture slowly
- Product properties that require special techniques
- Best sampling practices
- How to troubleshoot your standard sample prep procedures