If I measure the weight of the green beans per one cup. Then I measure the weight of the roasted beans per one cup. Would I get a proportional indication of moisture loss? I ask because most moisture indicators don't go bellow 5%. So if I ever new the initial moisture content of the green beans, I could estimate the moisture of the roasted beans.

Is the weight loss proportional to humidity loss or are there other variables that mess it up?

TX

There's the chaff weight and if you measure by the cup there will be bean expansion that will mean a less number of beans per cup after roasting.

TX FarmRoast.

I would then have to measure total weights (before/after) and compare them. Don't know if the chaff would add to much since it has very light weight, but it would be part of the equation.

Cheers

I find that a resulting high level of moisture remaining after roasting will show in the cup with an earlier unpleasant sourness taste in the aging of the roast.

TX FarmRoast. I'll keep it in memory

Cheers

Weighing all beans before and after roasting (not by volume, since beans expand) will show from 12% to 20% weight loss, depending on the degree of roast. Air roasters typically have 1% to 2% higher loss rates than drum roasters for the same degree of roast. The loss is mostly water and CO2. The technical literature I've read seems pessimistic about using weightloss as a quality or degree of roast indicator.

Whatever the initial moisture of the beans, by the end of the first crack, they will be down to their normal post roast levels. My theory on the early roast is that a lot of the character of the roast flavors, as opposed to the acidity, locks into place as the roast ramps into the first crack. I think there are variations in roast evenness and moisture at this point that doi not show up at the end of the first crack.

The Illy chapter talks about an expanding steam front, starting at the center of the bean and moving outwards like a slow explosion, that is responsible for the first crack. The timing of this front is modified by the drying period and first ramp. However, I have no information or speculation on how the timing of a steam front links up to the taste.

I use a one pound drum sample roaster, and almost always use the same charge weight (454g=1lb), and weigh the beans both before and after each roast. I roast for espresso only and generally to a level that is just at the end of 1st crack and a couple of degrees F before 2nd crack would begin. There is a lot of consistency in what I observe with my equipment in the weight loss before and after roasting. At the high end I'll have 18% loss (not common), at the low end 15% (rare) and most of the time it is around 16.5%, by weight. This is true with both dry and wet processed beans. By the time the beans get to me, they have probably equilibrated with approximately the same percentage of pre roast moisture, regardless of how they were processed.

After having done this for quite a while and having weighed countless batches of coffee, it is my opinion that small observed changes (such as 1% or less), in weight loss, are essentially meaningless and not predictive of roast quality. At this point, if I was to find a greater than 1% variation in post roast weight, I'd be more likely to think it was because I'd made an error in weighing out the green coffee that I roasted rather than that the observed difference was because of how the beans were roasted.

Of course, different equipment and different roast profiles/roast levels will produce different results, so you probably can't extapolate too much from my measurements, but you can become familiar with your own.

Some of what is happening is the loss of moisture in the beans, but also some of the physical matter of the beans is literally "going up in smoke," in much the same way that a log in your fireplace will weigh more before you burn it than afterwards.

ken

Thanks a lot for the great info. I saw in another thread about using a cheap humidity meter. This is the one I've chosen:

http://www.amazon.com/gp/product/B000UF ... oh_product

I'll give it a try when I get it. If it doesn't work for green beans I'll keep it for the house

Cheers