Moisture testing Analytics

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.

iBalance 601
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
0.01 Accuracy
9.99 8.91 10.8108% 10.8%
10.00 8.90 11.0000% 11.0%
10.01 8.89 11.1888% 0.3780% 11.2%
0.005 Accuracy
9.995 8.905 10.9055% 10.9%
10.00 8.90 11.0000% 11.0%
10.005 8.895 11.0945% 0.1890% 11.1%
0.002 Accuracy
9.998 8.902 10.9622% 11.0%
10.00 8.90 11.0000% 11.0%
10.002 8.898 11.0378% 0.0756% 11.0%
0.001 Accuracy
9.999 8.901 10.9811% 11.0%
10.00 8.90 11.0000% 11.0%
10.001 8.899 11.0189% 0.0378% 11.0%
0.0001 Accuracy
9.9999 8.9001 10.9981% 11.0%
10.0000 8.9000 11.0000% 11.0%
10.0001 8.8999 11.0019% 0.0038% 11.0%

One thought on “Moisture testing Analytics”

  1. As a footnote to this I was at Velvet Sunrise roastery in Stouffville and he had a Coffee Moisture Tester http://www.coffeelabequipment.com/COFFEEMOISTURE.html

    I brought several samples with me to try. The device is easy to use, took just seconds to do a reading and is non-destructive. Very impressive. I may change my tact concerning moisture testing.

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