Instructables

Question : Can you build a cheap Moisture meter for grain

Hello I'm a Peace Corps volunteer working with coffee. I'm helping farmers improve the quality of their coffee. To do this they need to dry their coffee very well. It is hard to tell if the coffee is dried enough without a moisture meter, and a moisture is very expensive. Does anyone know of how to build a moisture meter? this tells what percentage of the weight of the coffee bean is water, I believe. Or if anyone knows where to get one inexpensively, that would also help. Many thanks

lespaul745 years ago
Hi Peace Corps, For coffee to be considered specialty, it should have a moisture level between 10-12% or so, green. Moisture meters are quite expensive, but check out www.coffeechemistry.com, I saw a meter a while back under $500 - for green and parchment
Patrik7 years ago
Yeah - more info, please!

From your description, I assume we are talking about drying of the green coffee beans, not coffee roasting, correct?

Does this description of the drying process accurately reflect the situation you are dealing with?
What moisture level is the critical one to control? Do they need to be able to measure moisture content on-line, as they are drying? If not, how often/fast do they need to measure? How much can they afford to spend on this (i.e. is a commercial solution even achievable)?

Off the cuff, I'd say that electrical conductance and dielectric constant (capacitance) are two of the easiest measurements that should be correlated with moisture content. Grind some of the coffee fine, smash it between two metal plates, and you could measure both with a tiny microcontroller circuit.
eddieobrien (author)  Patrik6 years ago
Hi Patrik Many thanks for your response. Does this description of the drying process accurately reflect the situation you are dealing with? Yes, that site did explain my situation that I am dealing with. What moisture level is the critical one to control? the moisture level, in the bean, in its " green " form must be reduced to 12 % Do they need to be able to measure moisture content on-line, as they are drying? no, they can take it out and take a sample and measure the content If not, how often/fast do they need to measure? it would be nice to be able to test it every day, or spot check farmers drying operations. I would be good to get a result instantly, or at least with in a couple hours How much can they afford to spend on this (i.e. is a commercial solution even achievable)? 20 to 30 dollars. commercial units seem to be about 150 Many thanks for your comment, that website you sent was great Ed
If they have a small roaster, would it be feasible to do a light roast, and measure the weight before and after? 12% by weight should be fairly easy to measure, no? And I assume they do some test roasts of the beans anyway?

This page describes some of the gases produced and weight loss during roasting. Its sounds like after what they call the "first stage", the beans should be fully dried, with minimal weight loss due to chemical changes in the bean.
zachninme7 years ago
http://www.sparkfun.com/commerce/product_info.php?products_id=8227
Measures humidity, but same difference, right?
NachoMahma7 years ago
. Do you want to measure the moisture content while the beans are in the kiln or after they have been removed? What is the approximate target level? How accurate do you need to be? How cheap is cheap?
. Search for moisture sensor +coffee for some helpful info. Leave off +coffee to get an idea of the different ways to measure moisture.
. I'll guess that a wood moisture meter will not work well with whole beans. Ground coffee, maybe.
Austringer7 years ago
Harbor Freight Tools sells one pretty cheaply for wood. I'm not sure what you'd have to do to it to make it work with coffee beans. If a big pile of money fell out of the sky onto them, what kind of moisture meter would they run out an buy? It seems to me that Weissensteinburg's suggestion is pretty sound. Fill a plastic soda bottle (or whatever) with known dried beans and never open it. Then, when you think your beans are dry enough, fill a bottle with them and see how close they are on a simple balance.
NachoMahma7 years ago
. This may help.
Goodhart7 years ago
Could you do it based on before and after weight of the beans?