The final consumer may be a little unaware of this more technical type of instrument, but coffee producers, pickers and roasters are certainly familiar with the use of humidifiers. These are the moisture meters for coffee. They are also used for cocoa and other types of beans and cereals, but we will naturally focus on those for coffee.
Coffee and cocoa bean moisture meters are portable, easy to use, accurate, and not too cheap. Prices for coffee moisture meters can range from £70-80 for the simplest to the several hundred pounds that professional moisture meters cost.
Although they may look similar, and the novice user may be confused, coffee moisture meters have nothing to do with refractometers. Refractometers do not measure the humidity, but the density or concentration of the coffee in a liquid, and act on the coffee already brewed (the beverage), not on the bean. Make no mistake!
What a coffee moisture meter is used for
Coffee bean moisture meters are used after the harvest of the bean during the drying process.
Green coffee beans, after being harvested from the plant, contain approximately 45% to 55% moisture. However, the ICO (International Coffee Organization) dictates that green coffee must have a maximum moisture content of 8% to 12% before it is roasted.
The drying process is used to achieve these rates, and moisture meters for coffee beans are used to monitor the necessary drying time. Otherwise, it would be impossible to guarantee an optimum moisture level because moisture is not something that can be measured “by eye”.
There are many techniques and procedures for drying coffee beans, sometimes adapted to the specific characteristics of each bean or origin. But what never changes is the need to use a bean moisture meter to know when the coffee is just right.
The moisture content can have a crucial impact on how the coffee beans are roasted and how they taste afterwards, so the use of technical equipment and gadgets like this is more than justified if you want to achieve a good yield.
How moisture meters for coffee beans work
There are essentially two types of meters.
The more advanced ones, such as the Agratronix Coffee Tester, have a compartment where we put the beans or seeds whose humidity we want to measure. All you have to do is close the lid tightly and press the “test” button. After a few seconds, the display of the meter will show the degree of humidity of the bean and sometimes some additional data such as the room temperature.
These are fairly simple instruments, which are normally battery operated. The difficulty lies not in how to use the coffee moisture meters but in knowing how to read and interpret their data correctly and then make decisions regarding drying and subsequent roasting.
Here you can see one of these styles:
As you can see, the container in which the coffee beans are inserted for measurement is usually cylindrical and black.
On the other hand, we have moisture meters with an external connection. In these, we see a pair of pincers, probes or antennas, which are responsible for measuring the humidity. We must insert them into the food or grain we wish to test.
These meters are also battery operated.
Note: It is usually advisable to do several tests, about three or four, and to take the average moisture out of all of them. With a single test, the result may have some margin of error.
The best coffee moisture meter: Wile Coffee
In the world of humidity meters, there are usually two devices that are the absolute reference in the sector: The Agratronix meter and the Wile Coffee. Both are similar, and either will guarantee you the best performance and maximum precision. We are going to choose the Wile Coffee moisture meter for our review.
This is a battery-operated moisture meter for coffee and cocoa beans (not suitable for other ingredients) which is a perfect size to take with you to your harvest and work in the field. It has several profiles for different types of beans (e.g. arabica, robusta, parchment coffee), and the information is displayed on a simple digital LCD screen.
It comes with a practical carrying case, and measurements are quite fast (in the order of 20-25 seconds maximum).
The Wile Coffee moisture meter’s measurement range is from 1% to 36% moisture, with an accuracy of half a degree (+- 0.5%). Its price is obviously not low, but we must not forget that it is a device aimed at professionals.