It doesn't seem to track the graph; the wood formula responds a lot more strongly to RH changes than the coffee graph

another_jim wrote:The baking temperature is probably too low to drive off the CO2. If the CO2 stays in the coffee when it's roasted to 430F, it may release so slowly at 220F so as not to make much of a dent after 24 hours.
Fresh roasted coffee degasses over a week, but I do not think it loses 1.5% of its weight either in whole bean or ground form..

[sorry again for the OT]
Look in Illy's 2nd edition section 6.1.2. It specifically says that outgassing of CO2 results in a weight loss of 1.5-1.7%. It also says that volatiles other than CO2 are present in quantities similar to CO2, that "the rate of volatile compounds and gas release from coffee is strongly affected by temperature," and that grinding greatly speeds up the process.

At least the way I was doing it (grinding fairly fresh coffee, baking at 225F for 12-24 hrs), it is reasonable to assume that some of the weight losses I measured were due to loss of CO2 and volatiles. So my "moisture content" measurements were wrong.

I really don't know what to say Andy, except that you need to take it up with the ISO, the ICO and the Brazilian Coffee Board. Since oven baking is the calibration standard for measuring moisture in green and roasted coffee, it means if you are right, every measuring instrument used to measure coffee moisture is wrong.

Does roasted coffee lose 1.5% of its weight in a week? It would mean a company selling coffee in supermarkets would need to package 460 plus grams not to get violated on "net weight" standards.

Andy
Did it mean takes up 1.5-1.7% of the mass or of the weight? Of the mass I could see but not the weight. I did a number of samples a while back by grinding in a whirly blade and drying for a few hours at about 225 degrees weighing with a .01 scale and the results were right in the ballpark I would have assumed. I don't see where there would be any difference with roasted in a similar test. 7 grams of gas per lb?

another_jim wrote:I really don't know what to say Andy, except that you need to take it up with the ISO, the ICO and the Brazilian Coffee Board. Since oven baking is the calibration standard for measuring moisture in green and roasted coffee, it means if you are right, every measuring instrument used to measure coffee moisture is wrong.

I think oven baking is fine for green coffee. It just doesn't make sense for roasted coffee (if the material in Illy's book is to be believed).

As far as taking it up with the coffee NGOs, I'm not beating a drum on this. No worries, I just thought it was interesting.

another_jim wrote:Does roasted coffee lose 1.5% of its weight in a week? It would mean a company selling coffee in supermarkets would need to package 460 plus grams not to get violated on "net weight" standards.

Yup, it certainly does mean that. If any of the home roasters reading this wouldn't mind doing a simple experiment: seal ~100g of fresh-roasted beans in a valve bag and weigh the bag accurately once a week for a month or three. Something like this would make a good science fair project for your 6th grader!

farmroast wrote:Andy
Did it mean takes up 1.5-1.7% of the mass or of the weight?

Sorry, not being a physicist I don't understand the question. I thought that as long as we're measuring fairly close to sea level on the surface of the earth, there isn't much difference between the two measurements.

farmroast wrote:I did a number of samples a while back by grinding in a whirly blade and drying for a few hours at about 225 degrees weighing with a .01 scale and the results were right in the ballpark I would have assumed.

Right in which ballpark?

AndyS wrote:If any of the home roasters reading this wouldn't mind doing a simple experiment: seal ~100g of fresh-roasted beans in a valve bag and weigh the bag accurately once a week for a month or three.

I'll give this a try Andy. My guess is there may be a weight gain due to moisture absorbed.

gt wrote:My guess is there may be a weight gain due to moisture absorbed.

Good point. Maybe that's why, as Jim suggests, the companies selling coffee in the supermarkets don't have to add extra weight -- H2O replaces CO2.

I didn't have a valve bag handy but here's what I did. As soon as cooled (2-minutes), I put a batch from my P1 into an uncovered bowl and left in on the kitchen counter. Here's the bean weights I've measured.

2-min 170.7 grams
1-hour 170.4 "
4-hours 170.5
18 Hrs 170.7
24 hrs 170.9
2 days 171.1
3 days 171.3
4 days 171.5
5 days 171.7
6 days 171.8
7 days 172.0

I would guess in the summer when the humidity is up there would be more of an increase in weight.

It stays very close to constant. I wonder if when the balance of water and CO2 is just right the coffee will sparkle?