King Seven wrote:To be honest I am not sure exactly what I want to measure. It is all part of my grand unified theory of espresso, acidity and extraction. I want to understand the relationship between a coffees natural density, its density after roasting and other coffees that may have had different starting densities but are roasted to match the density of another coffee. If that makes any sense at all?
OK, this method will work, but this method might lose some stuff you're intrested in as well. You'll need some toys including a vacuum pump, thermocouple vacuum gauge (Hastings Teledyne is sufficient), container ( 1L volume or so) that can be sealed at the top and evacuated, balancce with sensitivity around .01 gm. You'll need a thermometer and barometer as well. None of this stuff needs to be real accurate if you're looking for density accuracy in the percent level. You can prolly find most of this stuff on ebay for reasonable enuff I guess.
Mount the sensor for the hasting teledyne vacuum gauge on the container. Determine the internal volume of the container. You can get this from geometry, weighing with water, or by weighing with the top open, then with the top closed and evacuated. You should get the same answer to within a few percent. You'll prolly be surprised to learn that the air volume within a 1L container weighs a little over a gram when atmospheric conditions are 101325 Pa and T is near 0C. Anyhoo the air weight value would be useful as a check of the vac gauge, and you'll need it later.
Find the density of the coffee. Fill the container with coffee to an arbitrary height. Weigh the coffee in air. Close the conatiner and pump out the air until you get a modest vacuum that remains relatively constant so that you can get a damn weighing (might take a while) and weigh it again. The difference in weight is the weight of the air plus any volatile stuff you pumped off. Unfortunately that could be water, which might or might not be important to you (is it?).
It's sort of the same idea as filling with water, but doesn't have problems with air bubbles. It's got other potential problems, but has the benefit that you can buy toys. And vacuum pumps are highly underrated in my view. If you have a vacuum pump you can make the coolest carbon fibre (special spelling since you're in da UK) espresso machine bodywork etc. and you can vacuum pack your green coffee too.
-Greg (man, you ask some tough questions) Scace