I am looking into getting a precision scale so that I can do green coffee bean moisture content analysis. Determining moisture content is a simple process. Samples of green beans are collected. Each sample set is weighed. The sample are then ‘cooked’ for 8 minutes at 160o F and the result weighed. The weight lost is the water. There are traces of volatiles lost also but water is the main content lost. For heating I am planning on using an infrared oven I have.
In looking at scales, accuracy is a key factor in cost. As a scale handles more weight, it is harder to get accuracy. As an example I am looking at the My Weight iBalance 601. This scale has a 600 gram capacity, can be connected to the computer via RS232 but only has a .01 gram accuracy. The iBalance 211 is twice as expensive, has only a a 210 gram capacity but is accurate to .001g.
The i601 is attractive as it could do both moisture measurement but also could do before and after roast weighing to record % loss due to the roast. My HotTop has a capacity of 250g. The key question is what is the accuracy of moisture content I could calculate with a scale of .01g accuracy.
In this table I assume 10 grams of green beans in and 8.9 grams out for an 11% moisture content. Then I vary the 10 and 8.9 values by the stated accuracy of the scales and calculate the moisture. The swing values are 10+ accuracy with 8.9- accuracy and the reverse 10- accuracy with 8.9+ accuracy. With .01g accuracy the moisture reading could vary by .4% while .005g accuracy reduces that to .2% accuracy.
From what I can see the lower end moisture meters use .01g accuracy.
|10 grams in||8.9 grams out||11% moisture content|
|Weight in||Weight out||Percent||Swing||Swing rounded|