another_jim wrote:It would be nice to have a cheap/quick/reliable way of measuring the moisture content of beans. I would think the drying phase would be proportional to the moisture content.

I have a suggestion that I am trying with some apparent success: when a greens shipment arrives i drop one of those RH/temp panel meters into the beans and seal them up in my 16C constant temp wine cellar. After 1-2 days stabilisation of temps & RH the meter reading for relative humidity gives a rough guide to moisture content - enough to adjust phase 1?

Just an idea given that green beans will take up in humid environments and lose in dry... is it worth developing? No doubt the actual number is bean and temperature specific.

Eric

Hello. 1st post to the forum!

I have also been interested in determining the moisture content of the beans I roast, as well as their density. In my uneducated guessing, I had theorized that the bean density would effect the roast more than the moisture content. Perhaps I am wrong about this? I do know that my density measurements are flawed somewhat by the moisture content, and the idea of drying the beans first seems like a good one to me.

For density, I start by weighing a small amount of green beans on my beam scale, and can get readings to about 5% of a gram. I then measure the bean's volume by fluid displacement in a graduated cylinder, which is fairly accurate to about [EDIT]25% of a milliliter. I then divide the weight by the volume to get density.

I am working off of a new Hot Top - P, and have only a handful of roasts under my belt with a drum roaster (it was iRoar before this). I hope that my density readings will help me fine-tune my roasts for different coffees.

Great first post Eric, welcome!

Thank you, sir. I look forward to learning and sharing with all of you here.

-= Eric

I looked up drying and density at origin in Sivetz's Coffee Technology, which is 1970s paleotech.

For moisture, moisture meters are calbrated against a ground sample weighed before and after a 225F 24 hour bake. Weigh immediately out of the oven to prevent moisture absorption. To get to the nearest 0.1 percent, you need a 0.1 gram scale and a 100 gram sample.

For density, he just took a big can, measured the volume (fill with water, weigh the water), dry the can, fill with beans, and shake until you can get no more in. Not quite a density, but a good relative scale.

Coffeengineer wrote:I have a suggestion that I am trying with some apparent success: when a greens shipment arrives i drop one of those RH/temp panel meters into the beans and seal them up in my 16C constant temp wine cellar. After 1-2 days stabilisation of temps & RH the meter reading for relative humidity gives a rough guide to moisture content - enough to adjust phase 1?

Just an idea given that green beans will take up in humid environments and lose in dry... is it worth developing? No doubt the actual number is bean and temperature specific.

Quoting myself, sad. No one took this up... definitely the fastest and a quite accurate method of measuring moisture content. What one needs is the sorption isotherm for green coffee beans in question for the measurement temp. Don't know how they change with temp. Measurement only takes 5 mins and requires no heating... I found a sorption isotherm for green coffee at 20C (variety not specified):

The x axis is equilibrium relative humidity (ERH).

Does anyone have access to one of these machines? It takes 24hrs to generate an isotherm that can then be used for rapid moisture content readings.

Now that I have sourced greens from different locations I am measuring ERH in the range 48% to 72%, certainly gives one a hint as to how long the drying phase should be.

Eric
ed: ERH (ratio of water mass in air) and water activity (ratio of water vapour pressures) are technically slightly different.

That's pretty awesome. Do you have a precise version of the graph?

Sorry Jim don't have details - the graph was quoted without a source... hence need access to a machine! It is a tedious exercise to generate the graph manually. A few sample points might be useful. Then again, for our use we don't know exactly how water content affects ramp up so might as well work with ERH directly.

Corollary of course is that green beans are constantly interacting with the environment, picking up and losing water depending upon the local RH, so one should keep greens in sealed containers if you don't want your profile to drift.

Eric