by bruceb » Mon Apr 07, 2008 10:50 am
Roasting=loss of moisture. Regardless of how you roast, loss of moisture is an exact measurement of how "dark" the beans have been roasted. If your roast to charcoal the product will be completely dry (ignoring the microscopic amounts of moisture that will immediately be picked up from the air duiring cooling). It should be apparent that there is no way to avoid weigh loss when roasting.
Storage of beans throughout the year will cause increases and decreases in their moisture content (if not hermetically sealed). Moisture content can be determined without roasting. You will need to accurately weigh an amount of beans, then dry them in the oven for a few hours at 125°C and reweigh. The loss of weight = the moisture content of the beans. Disclaimer: The dried beans will no longer be usable.
I store my beans in jute or paper bags in a cool room year round with humidity from 22% - 27% winter to summer. The moisture of the stored green beans is 10 -12%.
Edit: A couple more thoughts. I always weigh the beans immediately after roasting and note the weight or percentage in my roasting log. This value often tells more more about the degree of roast than the color of the beans.
The bean-specific moisture loss only plays a role when the beans just arrive, ie. from shipping and storage. If you store all of your beans in one room you will find that they all have about the same moisture content within a few days, and consequently the weight loss to a particular roast level will be about the same. In my experience coffee from India and Indonesia arrives with higher moisture levels than coffee from Ethiopia or South America. Again, however, once I store them a few days the moisture levels equalise.
Second edit: Corrected the values for bean moisture and room humidity.
Last edited by
bruceb on Mon Apr 07, 2008 3:00 pm, edited 1 time in total.
Three Francesconi (CMA) espresso machines - Rossi, San Marco, LaCimbali, Faema and 2 Mazzer Major grinders- CoffeeTech Maggionlino, Hottop, Alpenröst and HW Precision roasters. I decided I needed a bit of a change so I roasted some Monsooned Malabar. That was a change!