The FDA and USDA state that finished flour can reach a maximum of 15.0% moisture. Regulations on the maximum moisture can vary depending on the purpose of the flour. Flour packaged at a lower moisture percentage can be allowed to reach levels upwards of 16.0% for short periods of time without diminishing the quality of the flour or spoiling. Self-rising flour has a lower moisture maximum at 13.5% because too much moisture will start to catalyse the reaction that allows the dough to rise; the additives to the flour are more moisture sensitive than the flour itself.
A production manager at a gristmill contacted Hanna Instruments for help in finding an instrument that could measure moisture at the different stages of their milling process, particularly during the drying process and in the finished product. The manager needed something precise due to the potential for large losses if the wheat grains became damaged (burned, cracked, over-dried) during drying, and to ensure the finished flour would have an adequate shelf life.
Hanna Instruments recommended the HI903 Karl Fischer Volumetric Titrator. The HI903 has a wide range of measurement from 100ppm-100% moisture. Because of the high protein and complex carbohydrate content of flour, it is not suitable for direct injection into the titration cell. To accurately measure moisture content in flour, the water must be extracted from the flour over a few hours in a solvent containing formamide. The customer appreciated that the HI903 had built in calculations for the external extraction, prompting the customer to put in the sample mass, solvent mass, and solvent moisture content. A subsample can then be injected through the septum port into the cell. The customer appreciated the accuracy of Karl Fischer titration compared to the traditional oven drying method.
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