Measure the Moisture, Glean the Bean

Hey look, a parcel arrived!

After finding your optimal roast profile for a certain coffee bean, you run out of that specific bean and you take the next bag of a different origin of one that's supposed to be the same but it "works differently."

One cheap and simple test to prepare for these variables is to measure the density of the bean.

An additional method is measuring the moisture in the bean. There are two types of instruments to do this and they both observe the bean mass as if it was a component in electronics.

One of these treats the bean mass as if it were a resistor and it either measures a standard volume of beans to see how much current can flow through it or it measures the possible current between two pins of a "fork" that is stuck into a large bean mass, in a bag for instance. If the beans have more moisture inside them, they conduct electricity better.

The other method views the bean mass as a capacitor and checks how much electricity can be temporarily stored into it.

Some combine this with a weight and temperature measurement and some instruments use "all of the above" to get the most accurate results.

Can't wait to see

It is a fairly specialist market. Not every grain farmer has one of these and from research online I concluded that most rely on a hired hand to bring the measuring instrument along at harvest time. Also, the station where the harvest is stocked will have the instruments ready.

Even for coffee roasters it is not very common to have these things around.

Possibly the best available today is the Coffee Pro Moisture Mac, but it costs about $ 480 plus any customs fee that might be incurred (always a surprise element). I am considering to get one but I've been checking out some affordable alternatives as well.

I found one that comes with its own beautiful case for about half the price:

http://ksyuanhan.en.alibaba.com/productgrouplist-219357505/Grain_Moisture_Meter.html

Looks good!

It's a Wile65. You take off the black cap, fill the hollow cup with beans. On the inside, the cap has a metal disc with a strong spring behind it. The disc sits on an axis that goes up through the middle of the spring and in resting position it is just a little below the top of the black cap. So when you fill the cavity of the instrument with green beans and screw on the cap, you compress the beans, crunch them a little, into a slightly compacted tight bean mass to measure. This does not harm the beans so they can be roasted fine.

Cup to be filled with beans

On the left, the disc pushed down by a spring

Filled the cup

Screwed on the cap until the metal axis is level with the cap top

Reading results as if these were soy beans (surprise below)

Quoting from the manual:

Wile65 grain moisture meter is a LCD display multifunctional testing instrument, widely using, can measure with 16 different kinds of corn and other varieties of food according to the requirements.
Accuracy: ± 0.5%.
Grain measure range: 8-40%
Oil crop measure range: 5-25%

Prior to my order, I corresponded much with the agent of the company. Some businesses were closed the past Xmas / New Year days but I got prompt replies 24/7 as if there was no time zone and no days off. So here I want to express my gratitude to Beata Chu of the Kunshan Yuanhan Electronic Equipment Co., Ltd. --- Thankyou Beata!

I specifically wanted to know how useful this device would be to measure coffee beans. Beata had no experience with this application but she most willingly sent me all the data and manuals she could find for me.

The software of the device converts the outcome of the electronic measurement into the practical moisture result for the grain type that you have crunched into the measuring chamber. For instance, if you measure coffee beans with 14.7% of moisture, the same would mean 10.2% if they were soy beans and if you had loaded peanuts the electrical charge potential would mean they had 8.3% of moisture.

A standard Wile65 would need to be specially pre-programmed for coffee measurements (and that extra service comes at a premium to be paid) or you can use the device in a generic mode and work with a conversion table supplied by the manufacturer to see wat the reading means for coffee beans.

I was most pleasantly surprised to find that this Wile65 was already pre-programmed for coffee beans!


The next steps will be testing more beans and possibly comparing the readings with a calibrated similar device from another roaster. The device will already tell me if one batch of beans is less or more moist than a mother, which is very helpful to start with. A calibration puck can also be purchased. Or I could weigh, measure and then oven-dry the beans to compare this against their 0% moisture weight.

Without a personal business interest (I paid the full price through a Western Union agency) I wholeheartedly endorse the good people of the Kunshan Yuanhan Electronic Equipment Co., Ltd. It could be profitable to import and sell these but I'm more than willing to share my sources and work with others who want to get the same device. I'd love to hear your views if you get one.


PS My friend Gábor Laczkó sends me a link with reviews:

http://www.fwi.co.uk/machinery/8-popular-moisture-meters-put-to-the-test.htm